WO2013072319A1

WO2013072319A1 - Miniature dilatometer for measuring thermal expansion and magnetostriction, for use inside a multi-functional insert of a ppms device

Info

Publication number: WO2013072319A1
Application number: PCT/EP2012/072520
Authority: WO
Inventors: Jörg Faltin; Frank Steglich; Robert Küchler
Original assignee: MAX-PLANCK-Gesellschaft zur Förderung der Wissenschaften e.V.
Priority date: 2011-11-17
Filing date: 2012-11-13
Publication date: 2013-05-23
Also published as: DE102012109841A1; DE102012109841B4

Abstract

The invention relates to a novel miniature dilatometer for the capacitive measurement of the thermal expansion and/or the magnetostriction of a sample which can be arranged inside a device for measuring physical properties. To this end, the miniature dilatometer comprises a carcass which has a measurement cell diameter of less than 50 mm and a mass of less than 100 g, and preferably consists of a material with a thermal conductivity of > 200 Wm^-1K^-1 and a thermal expansion coefficient of < 17 10^-6K^-1. In addition, the invention relates to a method for producing such a miniature dilatometer, and to the use of same.

Description

Miniature dilatometer for measurements of thermal expansion and magnetostriction for use within a multifunctional insert of a PPMS instrument

description

The present invention relates to a novel miniature dilatometer for the capacitive measurement of the thermal expansion and / or the magnetostriction of a sample, which can be arranged within a measuring cell of the miniature dilatometer, wherein the miniature dilatometer can be arranged within a device for measuring physical properties. For this purpose, the miniature dilatometer has a body which has a measuring cell diameter of less than 50 mm and a mass of less than 100 g.

Furthermore, the present invention relates to a method for producing a miniature dilatometer for the capacitive measurement of the thermal expansion and / or the magnetostriction of a sample, which can be arranged within a measuring cell of the miniature dilatometer, wherein the miniature dilatometer within a device for measuring physical properties can be arranged. It is known from the prior art that a change in the temperature (T) or the magnetic field (B) on a solid causes a change in its external dimensions (ΔΙ_) in almost all cases. It is distinguished between a temperature-dependent changes in length and field-dependent changes in length. The former are referred to as thermal expansion, the latter as magnetostriction. Measurements of this change in length ΔΙ_ (Τ, Β), which are also referred to as dilatometric measurements, can help clarify a variety of physical issues. Areas of application lie, for example, in materials science, since there is often the interest in using a thermodynamic method to track phase boundary lines of a wide variety of materials in temperature-field phase diagrams. Here, dilatometry offers great advantages, in particular in that - in contrast to the otherwise often performed measurement of specific heat - the possibility of measuring anisotropies of monocrystalline samples exists. Especially important for precise measurements is a high resolution of the measurement (AL / L). This depends strongly on the type of method for determining the change in length AL. X-ray measurements enable resolutions in the range of 10 ^"5. Optical measurements permit a slightly higher resolution up to a range of about 10 ^{" 7} . By contrast, in the case of capacitive measuring techniques such as are provided in the miniature dilatometer according to the invention, higher measurement resolutions can be realized. As described in more detail below, are typical values for measurement resolution that can be achieved with the inventive miniature dilatometer, changes in the length of a sample at 0.05 A (0.05 x 10 ^"10 m) at a sample length of L = 5 mm. Capacitive dilatometers are already known from the prior art For example, the document AT 502 515 B1 discloses a capacitive dilatometer in which interference signals impinging on the sample, for example in the form of a torque generated by a magnetic field, are detected and detected To ensure that the solid to be measured in the magnetic field does not move in an undesired manner, the device described in AT 502 515 B1 is designed such that at least one capacitor plate or a carrier connected to this capacitor plate is overlapped by a tendon , which outside of the edge of the capacitor plate with adjustable holding force against egg n the other capacitor plate supporting element is pressed. Another special feature of this dilatometer is that the capacitor plate overlapped by the tendon is connected by means of only one tension-resistant pin connected to the movable support, in particular a threaded pin.

Furthermore, capacitive miniature dilatometers are also the subject of some review articles. For example, in "A miniature capacitance dilatometer for thermal expansion and Magnetostriction ", Rotter, M., Müller, H. and Gratz, E. in Rev. Sei Instrum., Vol.69, No. 7, July 1998, pp. 2742-2746 describes a miniaturized miniature capacitive dilatometer as far as possible. In the dilatometer described therein, two capacitor plates or two mutually opposite carriers for capacitor plates are pivoted to one another about a pivot point or a pivot axis and tensioned against each other by means of a resilient tension element Moreover, a disadvantage of the described dilatometer is that it can not be ruled out that at high applied magnetic fields a torque exerted on the sample or a force exerted on the sample can be excluded Force leads to a disturbing signal.

Another review article is by JJ Neumeier, RK Bollinger, GE Timmins, CR Lane, RD Krogstad et al. in "Capacitive-based dilatometer cell construed of fused quartz for measuring the thermal expansion of solids", Rev. Sei Instrum 79, 033903 (2008), doi: 10.1063 / 1.2884193 The dilatometer described therein is also a capacitive miniature This is between 5 K and 350 K. The essential feature of this dilatometer is that the change in length of the sample is determined by capacitance changes resulting from the In order to keep the relative expansion between the sample and the measuring cell as large as possible, the measuring cell in the described dilatometer is made entirely of fused quartz (silica) material with a = 0.5 × 10 ^"6 K ^" (at 20 ° C) one of the lowest known for solids thermal expansion coefficient, so that When a change in length of the sample results in a particularly large relative expansion between the sample and the measuring cell. In addition, this material, because it is electrically non-conductive, further constructive advantages. For example, an electrical insulation of the capacitor plates can be dispensed with.

In addition, miniaturized dilatometers are especially known for cryogenic measurements. Such a dilatometer is shown in FIGS. 1 and 2 and will be explained in more detail in connection with the corresponding description of the figures. In such a dilatometer, a sample is placed between a mobile and a fixed cell frame. Bound cell part arranged, which can be moved by means of an adjusting screw so that the sample is fixed. A change in the length of the sample leads to a displacement of a capacitor plate connected to it, which allows a resulting change in capacitance between it and a second capacitor plate to be measured. A particular difficulty with this design is the exact parallel alignment of the capacitor plates. For this purpose, a plurality of guide elements is provided, which, however, lead to a four-part and complex construction of the dilatometer. The object of the present invention is to provide a miniature dilatometer for the capacitive measurement of the thermal expansion and / or the magnetostriction of a sample, which can be arranged within a measuring cell of the miniature dilatometer, wherein the miniature dilatometer within a device for measuring physical properties can be arranged is to provide.

To measure the thermal expansion at higher temperatures (T> 30 K), the increased thermal relaxation time and the associated greater temperature sensitivity of the cell make it necessary to stabilize the temperature by means of an external device. For example, even at 300 K it is still necessary to stabilize the temperature of the cell and the sample to ± 0.01 K. It is therefore another object of the invention to provide a method for producing a miniature dilatometer and in particular a measuring cell for such a dilatometer with a cell material that provides the necessary high thermal conductivity and preferably a low coefficient of thermal expansion.

This object is achieved by a miniature dilatometer for the capacitive measurement of the thermal expansion and / or the magnetostriction of a sample, which can be arranged within a measuring cell of the miniature dilatometer, wherein the miniature dilatometer can be arranged within a device for measuring physical properties, which is characterized in that it has a body which has a measuring cell diameter of less than 50 mm and a mass of less than 100 g. Preferably, the body of the miniature dilatometer consists of a material with a thermal conductivity> 200 Wm ^"1 K ^{" 1} and a thermal expansion coefficient <17 10 ^"6 K ^'1 .. Due to the small size and low mass of the body and / or the large thermal conductivity and / or the low coefficient of thermal expansion, it is preferably possible that the miniature dilatometer is adapted to the temperature of a measuring cell of the miniature dilatometer and the sample at least in the range of 5 K - 200 K, preferably in the range of 10 mK - 300 K to ± 0.01 K to stabilize and at least in this temperature range measurements of thermal expansion with a maximum sensitivity of AL / L of 10 ^"8 to 10 ^{" 10} , preferably AL / L of 10 ^"9 to 0 ^"10 and / or measurements of the magnetostriction of up to 10 Tesla or more, preferably 20 Tesla or more, in this regard, it should be understood that this e sensitivity can be achieved with such a miniature dilatometer, but not inevitably must be achieved with each measurement. Of course, with a miniature dilatometer measurements of lower sensitivity can be made. For example, with extremely rapid temperature changes, despite the low mass of the miniature dilatometer, the temperature of the sample can easily be delayed, so that the measurement accuracy or the sensitivity does not reach the maximum possible value. Likewise, other factors such as variations in the magnetic field, faulty sample preparation, or other influences could result in the maximum sensitivity not being reached for a particular measurement.

The dilatometer can thus be used with a sensitivity of up to AL / L of 10 ^"9 to 10 ^{" 10} in a wide temperature range in which it and the sample can be stabilized in a short time to ± 0.01 K.

An essential advantage of such a dilatometer is that it can be dimensioned so small that it can be arranged within a multifunctional insert of a device for measuring physical properties, such as, for example, a physical property measurement system (PPMS) from Quantum Design (see FIG. 7 right, left). Such PPMS devices are widely used in research institutes, so that, for example, by using a miniature dilatometer according to the invention in combination with such a PPMS device, it is possible, for example, to measure changes in the length of samples with a high degree of accuracy and reproducibility. In addition, the miniature dilatometer of the present invention can be manufactured at comparatively low manufacturing costs as compared to the dilatometers known from the prior art. The achievable sensitivity of a dilatometer is limited, among other things, by the size of the capacitor plates, their distance from each other and their plane-parallel alignment. The maximum sizes of the capacitor plates are limited in a miniature dilatometer, which is to be used in a PPMS device with predetermined maximum measuring cell dimensions. There is therefore a particular difficulty in enabling a high maximum sensitivity (AL / L) of .gtoreq.10.sup.- ⁸ , preferably even 10.sup.- ⁹ with a particularly small dimension of the measuring cell diameter of less than 50 mm.

In order to optimally utilize the available space inside a PPMS device, in a miniature dilatometer an outer surface of the body of the measuring cell preferably has essentially a shape of a straight cylinder, wherein a lateral surface of the straight cylinder has at least two plane-parallel regions and the body on at least one base or top surface extending in the direction of the height axis of the cylinder first recess having at least partially circular cross-section, which forms a carcass interior. With respect to the outer surface of the body in the form of a straight cylinder is noted that this is not limited to the shape of a right circular cylinder, but the cylinder may have any suitable surface geometry. As is apparent from the above-described description, a substantially circular base surface is preferably provided with two mutually oppositely disposed, parallel circular chords which in the respective region represent the outer boundaries of the base surface. The base area corresponds in this case to a circle which is reduced on two opposite sides by, preferably equal, circular segments.

By means of this embodiment, it is possible to make the interior of the carcass with an at least partially circular cross-section particularly large and on the one hand to create a particularly large sample space and at the same time to reduce the amount of material of the measuring cell to a particularly low level. Furthermore, it is preferred that the body of the measuring cell has at least one first passage opening, preferably with a rectangular cross section, which is arranged in a first outer wall section of the straight cylinder and starting from this first outer wall section perpendicular to the height of the straight cylinder in the direction of the first recess , Preferably up to a second outer wall portion opposite the first outer wall portion, preferably parallel to the plane-parallel portions of the outer wall extends. Thereby, a further material and thus weight entry is possible and at the same time given the opportunity to get laterally into the interior of the sample space.

Due to the wide temperature and magnetic field range in which the miniature dilatometer should be used, the choice of materials is very limited, as this results in special material requirements for the cell. This in turn also results in special requirements for a method for producing a measuring cell for such a dilatometer. It is therefore a further object of the invention to provide a method for producing a dilatometer with particularly low manufacturing tolerances.

In addition, the induction currents occurring in the case of a time-varying magnetic field in the measurement of the magnetostriction in the cell material can lead to the formation of a magnetic moment which, in interaction with the external magnetic field, exerts a torque on the moving parts of the measuring cell. This torque can cause the capacitor plates to move relative to one another, e.g. tilt, which can result in a distortion of the measurement signal. It is therefore desirable to make the measuring cell for the dilatometer of a cell material of lower conductivity in order to make it possible to keep said induction currents as small as possible.

In addition, the magnetostriction coefficient of the material should be as low as possible in order to prevent undesired cell effects caused by magnetostriction of the cell material from dominating the measured values.

A particularly suitable material for use in a measuring cell of a miniature dilatometer copper-beryllium alloys have shown. Therefore, an embodiment of the miniature dilatometer in which the measuring cell of the miniature dilatometer is at least partially a copper-beryllium alloy having a beryllium content is preferred from 0.5 to 5 wt .-%, preferably 1 to 2.5 wt .-%, particularly preferably from 1, 5 to 2 wt .-%, particularly preferably from 1, 84 wt .-%. This alloy has proven to be particularly suitable to be temperature stabilized by external devices. In particular at higher temperatures (T> 30 K), this alloy offers advantages since its temperature can be stabilized particularly well by an external device despite the increased thermal relaxation time and the associated greater temperature sensitivity of the cell. With a measurement at 300 K, it is possible for a measuring cell made of the mentioned copper-beryllium alloy to stabilize the cell and sample to ± 0.01 K. In a further preferred embodiment of the miniature dilatometer, changes in length of the sample to be measured, arranged in the miniature dilatometer, can be determined via a change in the electrical capacitance between the sample and at least one capacitor plate, preferably by means of a precision capacitance measuring bridge. Thereby, the above-mentioned particularly high maximum sensitivities AL / L of 10 ^{^"8} to ^{10" 10,} preferably are ^"9 to ^10" by ¹⁰ reaches 10th

In order to set and / or maintain the temperature stability and in particular the temperature distribution in the interior of the measuring cell as uniformly as possible (in particular during a measurement), it is advantageous to subdivide the measuring cell into as few sections as possible, between which temperature equalization is made more difficult. Boundaries between individual sections can be, for example, intermediate spaces between individual components or changed material compositions between individual sections. In order to reduce or exclude resulting temperature gradients within the measuring cell, the body of the measuring cell is formed in a preferred embodiment of less than 8, preferably less than 5, preferably less than 3 parts, more preferably only one piece. This makes a more compact design possible. The part (s) is / are preferably shaped so that it is / are preferably producible by milling and / or spark erosion. By manufacturing the body of the measuring cell from a few, more preferably from a single part instead of from several parts as known from the prior art, there is the advantage that fewer errors can occur during production. For several parts, there is a certain deviation from the nominal dimensions for each part. Even if the respective fault tolerance is low, with a large number of components, the respective incorrect error to a comparatively large error or a large deviation from the setpoint. Thus, in the manufacturing method of the present invention, it is possible to reduce the error tolerances. Consequently, according to the new method, it is possible to manufacture a cell or a body with particularly small deviations from the desired geometry. In such a body it is therefore possible to align the capacitor plates exactly (ie with a smaller error) in parallel.

Furthermore, the cell of the present invention offers the possibility for magnetostriction measurements to select suitable materials from a particularly wide variety of materials. By selecting particularly suitable materials, e.g. the mentioned Cu loading

Alloy can be achieved that the resolution in magnetostriction measurements is as good as that of measurements of thermal expansion. In the case of measuring cells known from the prior art, which are made, for example, at least partially of silver, on the other hand, increased noise occurs during magnetic field sweeps, which can be regarded as the result.

Next Favor is an embodiment of the miniature dilatometer in which in the body ring springs, preferably leaf springs, are integrated, which are preferably integrally formed together with the body. This one-piece design makes it possible for the temperature of the springs to be adapted quickly to the measuring temperature. A significantly delayed adjustment of the temperature of the spring can be avoided because due to the one-piece embodiment, there is no barrier for temperature compensation between the body and spring, for example in the form of a gap or a material boundary. As already described, the use of a miniature dilatometer in a PPMS device offers advantages. For this, however, it is necessary that the miniature dilatometer has particularly small outside dimensions, which allows integration into a designated space within the PPMS device. The measuring cell of the miniature dilatometer therefore preferably has a cell diameter of less than 50 mm, preferably less than 30 mm, particularly preferably 26 mm or less, preferably a construction height of less than 50 mm, preferably less than 30 mm, preferably less than 25 mm, particularly preferably of 21 mm or less and more preferably a width of less than 50 mm, preferably less than 30 mm, preferably less than 25 mm, particularly preferably 20 mm or less. The measuring cell, which has been reduced to a minimum in size and mass by the new production method, has great advantages in terms of its application in comparison with the measuring cells known from the prior art. In particular, the extreme miniaturization, the installation of the dilatometer even with limited space available. The entire mass of the measuring cell can be significantly reduced by the described miniaturization compared to known from the prior art dilatometer. Despite the reduction of the outer dimensions, it is possible to keep the width of the capacitor plates and thus inevitably also the associated resolution power comparatively large. Due to the reduced cell mass and the reduction to a few individual parts, the thermal equilibrium state can be set much faster than in measuring cells known from the prior art. Among other things, this results from the reduction of the number of material transitions (eg gaps) arising between the individual components, which impede unimpeded heat transfer over the entire measuring cell. The speed of setting a homogeneous temperature within the measuring cell is largely determined by the thermal conductivity of the measuring cell and their mass. As already described above, highly thermally conductive materials for the measuring cell, such as the copper-beryllium alloys mentioned, are preferred. For particularly rapid adjustment of a homogeneous temperature within the measuring cell is further preferred that the measuring cell is particularly easily formed, that has a particularly low mass. It is therefore preferred that the measuring cell of the miniature dilatometer has a weight of less than 75 g, preferably less than 50 g, particularly preferably 42 g or less.

In contrast to the known from the prior art apparatuses of thermally highly conductive materials, the cell of the invention is therefore even suitable for measurements of thermal expansion, even if the preferred copper-beryllium alloy has a lower thermal conductivity than, for example, silver or copper , as used in other apparatus for such measurements. Due to its intrinsic properties, the copper-beryllium alloy used is particularly suitable for measurements of magnetostriction. Thus, with such a dilatometer, it is possible for the first time to carry out measurements of the magnetostriction as well as of the thermal expansion in the abovementioned resolution in one device. The measurement resolution is significantly dependent on the size of the capacitor plates, as their Radius in the second power is included in the calculation of the capacity. Since a comparatively large internal space can be created by the new production method with particularly small external dimensions of the measuring cell, the extraordinarily high resolutions of AUL of 10 ⁸ - 10 ¹⁰ or even 10 ⁹ - 10 ¹⁰ can be realized, as described below , typical values for the measured with a measuring cell of the present invention, changes in length of a sample of 0.05 a (0.05 x 10 ^"10 m) at a sample size of L = 5 mm.

Preferably, the miniature dilatometer can be used in a capacity range which includes a capacity range of 1 to 250 pF, preferably of 5 to 50 pF, preferably of 20 to 25 pF. The capacitor plates can be connected in various ways with the body. Alternatively, for screwing, for example, a bonding is possible. But all other types of connections are theoretically conceivable. By gluing the capacitor plates, the background of the respective measurements can be further reduced and thus the calibration of the cell even easier and more accurate.

The particularly high resolution of AUL of 10 ^" 8-10 ^{" 10} and preferably even 10 ^" ^{9-10 10} is another positive aspect of the present invention, which is determined by the distance of the capacitor plates from each other and the diameter of the respective capacitor plate Due to the new manufacturing process, it is possible that the width of the cell is determined almost exclusively by the width of the capacitor plate.Thus, based on the capacitive measuring method is currently at a given maximum measuring cell size (eg by the dimension of the corresponding rum in a PPMS device ) no higher resolution achievable.

The resolution depends on the adjustable measuring capacity. In particular, it is proportional to the square of the measurement capacity. For example, the measuring cell of the present invention may be operated at a measuring capacity of approximately 25 pF. Thus, for example, with a measuring capacity of 25 pF, the resolution is 625/25, which is about 40 times better than that of a measuring cell operated at a capacitance of 5 pF.

Furthermore, it is preferred that the measuring cell of the miniature dilatometer can be integrated in standardized measuring systems, in particular in a Physical Property Measurement ^System® , the company Quantum Design. This is a particularly accurate attitude, upright tion and change of the measuring conditions as well as an exact recording of the measuring results.

For precise temperature monitoring, it is further preferred that a thermocouple can be integrated into the body of the measuring cell or that it can be arranged in the interior of the device for measuring physical properties in the immediate vicinity of the body of the measuring cell. In particular, by the embodiment in which a thermocouple is integrated into the body of the measuring cell, a particularly good temperature transition between the sample and the thermocouple is possible, so that ren with a very small number of Barrie- that would prevent a uniform temperature distribution, the temperature the sample can be recorded and recorded directly in the measuring system and during the measurement.

Preferred temperature sensors in the miniature dilatometer are sensors with response times <50 ms, preferably <25 ms, preferably <15 ms, preferably <10 ms, preferably <5 ms, preferably <2.5 ms, particularly preferably about 1 , 5 ms or less at 4 K and <150 ms, preferably <100 ms, preferably <75 ms, more preferably used by about 50 ms or less above a temperature of 77 K. These fast response times allow a particularly accurate detection and, if necessary, adjustment of the temperature. It is preferred that the variations in temperature control (e.g., by the above-described measures) be less than 1 mK even at high temperatures (e.g.,> 50K).

In addition to the sensor's fast response time already mentioned above, it is useful for a sensor, e.g. a sensor of a thermocouple, which is used in such an apparatus, advantageous if the deterioration of the sensor by external magnetic fields is low. Preferably, the impairment is so low that possibly resulting measurement errors are negligible. If these o.g. Conditions are met, a thermometer is particularly well suited for both temperature and magnetic field sweeps.

Preferably, a miniature dilatometer is used according to one of the embodiments described above for the capacitive measurement of the thermal expansion and / or the magnetostriction of a sample. As can be seen from the embodiments described above, making such a miniature dilatometer can be extremely difficult. It is therefore also an object of the invention to provide a method for producing a miniature dilatometer.

This object is achieved by a method of manufacturing a miniature dilatometer in which the body of the measuring cell of the miniature dilatometer is composed of less than 5 individual parts, which are produced by milling and / or spark erosion.

Preferred is a method for producing a miniature dilatometer, wherein the body of the measuring cell of the miniature dilatometer consists of a single part, which is produced by milling and / or spark erosion. The process for the production of the body requires special process steps which make the production more difficult compared to processes known from the prior art. Especially due to the additional miniaturization special care is necessary. A great difficulty is e.g. to clamp and guide the erosion wire in such a way that all slots and recesses in the body can be created according to the requirements.

In order to allow the exact removal of material by milling and / or spark erosion of the materials used in the necessary precision, a method for producing a miniature dilatometer is preferred in which a piece of material from which the body of the measuring cell of the miniature dilatometer or the parts of the body of the measuring cell of the miniature dilatometer is / are prepared before milling and / or the spark erosion over a period of 0.5 - 48 hours at temperatures of 100 - 750 ° C, preferably over a period of 1 - 5 hours at temperatures of 250 - 500 ° C, more preferably over a period of 2 - 4 hours at temperatures of 300 - 350 ° C, annealed / are.

Further advantages, objects and features of the present invention will be explained with reference to the following description of the appended drawing, in which an example of a miniature dilatometer is shown. Components of the miniature dilatometer, which in the figures At least substantially coincide in terms of their function, this can be characterized by the same reference numerals, these components need not be quantified and explained in all figures.

Show it:

Fig. 1: a dilatometer according to the prior art;

2 shows further views of the dilatometer shown in FIG. 1 in a side view (left) and exploded view (right);

3 shows an illustration of a measuring cell which has been reduced in height compared with the prior art (left) and an embodiment of a measuring cell (right) consisting of particularly few individual parts;

4 shows a schematic representation of a capacitor arrangement with inhomogeneities at the edges of the capacitor plates;

5 shows an illustration of a measurement setup for the function test (left) and a comparison of determined measured values with calculated values (right);

Fig. 6: Results of the determination of the spring constant of the dilatometer (left) and the determined force acting on the sample at working capacities of 20 - 25 pF (right);

7 shows a schematic representation of a PPMS device (left) and a measurement setup with dilatometer insert and measuring computer (right);

Fig. 8: a dipstick for insertion into a PPMS device with Dilatometereinsatz, thermally conductive springs for thermal coupling to the PPMS device and measuring connections for capacitance and temperature measurements (below) and a section of the dipstick with a cell of the Dilatometereinsatzes including Temperature sensor (highlighted by white rectangle) (top); 9 shows a comparison between measured values of the relative expansion AL / L and literature values of the relative extent AL / L of a copper sample;

10 shows a comparison between measured values of the relative expansion AL / L and literature values of the relative extension AL / L of a silver sample;

11 shows a comparison of the expansion coefficient a between measured values and literature values of the relative extent of a silver sample;

12 shows a representation of the relative error between measured values and literature values of the relative extension AL / L of a silver sample (left) and of the expansion coefficient a (right);

13 shows a representation of the results of a measurement of the extent AL of a copper sample in the temperature range from 9.5 to 10 K;

FIG. 14 is a perspective view of a body of a measuring cell; FIG. and

FIG. 15 shows perspective views of a body of a measuring cell (top right and bottom right) and schematic plan views and / or sectional drawings of a body of a measuring cell; FIG.

Referring to Figures 1 and 2, a miniaturized dilatometer known from the prior art is shown specifically for cryogenic measurements in various views. In such a dilatometer, a sample 104 is placed between a platform of the movable cell part 106 and a punch 102 connected to a cell frame 103. This can be moved by means of an adjusting screw 101, whereby the sample can be fixed. When changing the length of the sample, the movable part of the cell shifts by the amount of this change in length, whereby the upper capacitor plate 107 connected thereto is also displaced. This leads to a change in the distance of this upper capacitor plate 107 with respect to the fixedly mounted on the cell frame lower capacitor plate 108. In order to ensure a parallel alignment of these opposite the lower capacitor plate 108 during the displacement of the capacitor plates 107, the movable part with two annular springs 105 with the cell frame connected. Through the parallel geometry, it should be possible for the frame to move in the vertical direction, but preferably not to tilt or tilt. The capacitor plates 107, 108 themselves are electrically insulating fitted in their respective frame pieces. At the level of the lower capacitor plate 108, the cell frame can be separated. This allows alignment of the plates 107, 108 relative to their frame pieces. By lapping the plates 107, 108 installed in the frame pieces, a uniform surface plane of the capacitor plate 107, 108 and frame 103 is created so that the capacitor plates 107, 108 are in a plane-parallel position after assembly of the cell.

The cell shown in Fig. 1 is designed to achieve 0.25 mm plate spacing in the relaxed state, which corresponds to an "empty capacity" (capacity without sample introduction) of 5.4 pF. For a sample installation, it is necessary that the plate spacing is reduced by means of the adjusting screw 101 to a working capacity of 20 pF. Changes in this working capacity - and thus changes in length of the sample to be measured - can then be detected in the course of a measurement. In the example shown, a resolution of approximately 10.sup.- ⁷ pF is possible (for example with a measuring bridge AH 2450 from Messrs. Andeen Hagerling) An analogous method for determining changes in length is described by Pott and Schefzyk in J. Phys E: Instrum. , Vol. 16, 1983.

The body of the cell, e.g. in the dilatometer shown in the prior art and shown in Figs. 1 and 2 is composed of at least 8 individual parts, in the subject of the present invention is preferably formed from a single piece, as shown in Fig. 3 (right). As a result, a significantly more compact compared to the prior art construction is possible. The body 50 in this case contains the movable cell part, the ring springs, as well as a part of the cell frame (see Fig. 2, all parts in each case within the white rectangle).

In particular, in the fabricated body 50, the ring springs are already included, which makes it necessary to anneal the CuBe block prior to fabrication. As a result, the Vickers hardness of the material by a factor between 1, 5 and 5, preferably increased by about a factor of 3, whereby the necessary stability while ensuring high elasticity of the necessary for a parallel vertical displacement of the movable member relative to the cell frame springs become. Compared to a cell known from the prior art, as shown on the left in FIG. 3, it can be seen that the size of the cell is significantly reduced. In particular, it is possible to reduce the cell width 16, thereby enabling the incorporation of such a cell into a multifunctional insert of a PPMS device. With a cell diameter of 26 mm, a height 8 of 21 mm and a width 16 of 20 mm could be realized. It was possible, despite this reduction in dimensions, to ensure stability and functionality of the springs contained in the body 50, which are necessary for the function of the measuring cell.

FIG. 4 shows a schematic representation of a capacitor arrangement 60 with inhomogeneities at the edges of the capacitor plates 61 and 62. These represent a possible source of error in the measurement data determination. In an ideal plate capacitor of the area A and the plate spacing d, the capacity applies

C = e ^ A / d (2. 1) with the electric field constant θο = 8.8562 x 10 ^"12 F / m, he as the dielectric constant of the medium between the plates, A of the capacitor surface and d the distance between the capacitor plates 61 and 62. In the cryostat (continuous cryostat), the dilatometer is operated under vacuum so that e ^ = 1. In dry air at room temperature and a pressure of 1 atm (1, 0133 · 10 ⁵ N / m ² , 1 , 0133 bar) e ^ has a value of 1,0006, the above-mentioned equation can also be used for measurements outside of the vacuum In the PPMS, a small amount of helium with a gas pressure of about 1 mbar serves as replacement gas for better thermal coupling of the In this case, too, it can be assumed to be approximately a value of 1, since the corrections to this value are in the order of 10 ^{"9 over} the entire temperature range of 2 - 300 K.

When dimensioning the upper, preferably smaller, capacitor plate 61 with a radius (r) of preferably less than 15 mm, preferably less than 10 mm, for example 7 mm, the capacitance changes from the starting value C ₀ to the value C a Change of the distance around Ad = ebp r ² (C - C ₀ ) / (C - Co) (2.2) or (with combined constants)

Ad [1 CT ⁶ cm] = -1, 3898 x 10 ⁵ pF * (C-C ₀ ) / (C * C ₀ ) (2.3)

The minus sign arises as the plate spacing d decreases as the sample expands. The capacitance measured in the experiment is typically a few tens pikfarad.

Equation 2.2 only applies to ideal plate capacitors. For the real developed cell of the present invention, it is necessary to include additional correction factors that compensate for deviations from ideal behavior. For example, it is possible that the absolute value of the capacitance changes due to distortions of the electric field at the edge of the capacitor plates. The resulting relative capacity deviation is according to Maxwell

AC / Co = w / r · d / (d + 0.22w) (2.4) where w represents the distance between the top plate and the guard ring (as shown in Fig. 4). With a radius of the upper plate of r = 7 mm, the distance between guide and plate edge w = 0.05 mm and the determined working distance of the plates of eg d = 50 pm, this results in a deviation AC / C ₀ of about 0.5%. This can be assumed to be constant for the entire temperature range.

Furthermore, corrections may be necessary, taking into account that the plate radius r could change with temperature. The correct relationship for the determination of the expansion results

Ad = eop ^ ((C-C ₀ ) / (C · C) - (2 Ar / (r ₀ · C)) (2.5), with ΔΓ / Γ ₀ as the thermal expansion of the plate material CuBe known from the literature, based on 5 K. Accordingly, results for the maximum error over the entire temperature range, a value of about 1%. The greatest influence on the accuracy of the measurement result has minimal misalignments of the capacitor plates assumed to be absolutely parallel in 2.2. Due to the dependence of 1 / d in 2.1, the real change in length of the sample is smaller than calculated by 2.2 in the case of capacitor plates tilted with respect to one another. The correct relationship is therefore

Ad = eoP ^ C - C ₀ ) / (C · C ₀ ) (1-OC ₀ / C _max ² ) (2.6)

C _ma ² indicates a short-circuit capacity which has been determined experimentally for the cell according to the invention. In combination with the working capacity C ₀ of ^~ 20 pF, this results in an additional error of approx. 2.2%. In order to obtain a particularly good resolution, the working capacity C ₀ should not be chosen too small, since the resolution capacity of the measuring cell, ie the measurable change in capacitance for a given change in length

AC ~ AL'C ₀ ² grows quadratically with the basic capacity C ₀ . In turn, a very large C ₀ would cause a larger systematic error due to the influence of plate tilting. A value for C ₀ of about 20 pF has proved to be a suitable compromise in the experiments carried out.

Since the errors described above are comparatively small and systematic in nature, they can be compensated for by a calibration, and therefore equation 2.2 can be used below to calculate the actual change in length.

In order to check the correct functioning of the dilatometer according to the invention, the validity of relationship 2.6 was initially checked, neglecting effects on the plate edges. For measuring the change in length, a commercially available dial gauge with a resolution of 1/00 mm was used. As shown on the left in FIG. 5, the probe of the dial gauge is placed vertically on the upper side of the movable frame part in the measurement setup. When tightening the micrometer so the vertical displacement of the moving part of the cell, including the associated upper capacitor plate, measured. At the same time the change of the capacity at the connected measuring bridge can be observed. 5 shows on the right the comparison of this measurement and the values calculated from equation 2.6 for different short-circuit capacities. As can be seen from the figure, the experimentally determined values within the measurement accuracy agree with the values calculated for c _max = 150 pF. Although the Reading accuracy of the dial gauge with 5 μιτι at best to assess as relatively low, however, the experiment shows that the measured change in length is accurate to about 3%.

In addition, the maximum capacity can be approximately checked by carefully tightening the adjusting screw until the short-circuit is reached. The highest capacity reached before is recorded. This approach is in some ways arbitrary, since the plate spacing can be adjusted with only limited accuracy. However, to measure the short-circuit capacitance, an infinitesimal plate spacing must be set. The C _max value determined for this method was 130 pF, confirming the value of 150 pF determined by the simple bump test.

The springs, preferably leaf springs of the movable part of the cell, exercise during clamping a force on the sample, which can lead to an influence on the measurement parameters. For example, this can lead to a shift in the TP phase diagram. It is therefore necessary to determine the force constant of the leaf springs used in the cell construction. For this purpose, the movable cell frame is loaded with weights of up to 150 g and the resulting displacement of the mobile cell part is estimated from the resulting change in capacitance. In FIG. 6, the left side of the determined linear relationship between the change in length and the acting force is shown, from which the spring constant of, in this example D = yields 24291 Nm ^" '. At low temperatures, the elastic modulus of copper alloys changes only slightly. Therefore, this value can also be assumed for later operation in the cryostat.

In the right part of Fig. 6, the relationship between the set capacity and the present plate spacing or the resultant force is shown. Capacities of 5 to 50 pF, preferably for example 20 to 25 pF, are suitable for the working area of the cell. 20 - 25 pF correspond to a plate spacing of 50 - 31 pm and a spring force on the sample of approx. 3 N. One aspect of the invention is the possibility of being able to integrate the measuring cell into standardized measuring systems. For example, the measuring cell of the present invention offers the possibility of being able to be integrated into a device for measuring physical properties, such as a Quantum Design Physical Property Measurement System (PPMS). This system is specifically designed for the automated flow of measuring Process designed equipment with which, for example, continuous temperature weeps in the range of 5 to 400 K are possible. The lowest non-continuously attainable temperature of this system is 2 K. By means of a superconducting magnet, field strengths of more than 5 T, preferably more than 7 T, preferably more than 8 T, particularly preferably up to 9 T and more can be achieved ,

As shown schematically on the left in FIG. 7, the exemplary apparatus consists of an outer layer of superinsulating material. Inside it is followed by a layer of liquid nitrogen. This is followed by a vacuum zone, which encloses an internal helium tank and thermally insulates. Inside the helium tank is a cooling ring chamber.

In the lower part of the Kühlringringkammer an impedance is arranged, through which helium is pumped. By means of a thermocouple, e.g. a heater, the temperature of the flowing helium is adjustable. As a result, or by the helium, it is possible to adjust the sample to the desired temperature.

Commercially, a variety of measurement applications for such apparatus, such as e.g. the PPMS available. Thus, for example, already calibrated and operational inserts for measuring the resistance and the specific heat are known. Due to the small dimension of the area in which a measuring cell can be arranged within such an apparatus and other complex technical difficulties, is not a functional use for measuring the thermal expansion and magnetostriction for such an apparatus, in particular for the o.g. PPMS system known which the resolution ΔΙ_ / Ι_ of

10 ^"8 - 10 ^{" 10} reached. By the manufacturing method according to the invention, it is possible to make the inner region of the measuring cell, in which the sample and the capacitor plates are arranged, particularly large at given external dimensions. In particular, this makes it possible to design the capacitor plates larger than known from the prior art for such systems that can be integrated into measuring apparatuses. As a result, a significant increase in the resolution by a factor> 10 is possible. In addition, the space-saving design of the body of the measuring cell offers the possibility of integrating a thermocouple (eg a thermometer, a temperature-sensitive measuring cell or similar) into the measuring cell or arranging it in the immediate vicinity of the measuring cell. Preferably, the thermocouple is in direct contact with the measuring cell or even the sample, so that the Temperature of the sample can be determined very accurately. Furthermore, the thermal balance can be adjusted quickly. In dilators of the prior art, which are also designed for the arrangement within a multifunctional use of a PPMS device, this is not possible. In practice, therefore, these measuring cells result in inconsistencies in the calibration and the reproducibility of the results.

As shown on the right in FIG. 7, the present invention has succeeded in providing a dilatometry measuring station with a PPMS system as a cooling unit. Due to the particularly small dimensions of the measuring cell according to the invention, these could be arranged within a commercially available multifunctional insert.

Fig. 8 shows a dipstick for insertion into a PPMS instrument with dilatometer insert, thermally conductive springs for thermal coupling to the PPMS instrument and measuring connections for capacity and temperature measurements (bottom) and a section of the dipstick in which the cell of the dilatometer insert inclusive of the temperature sensor (highlighted by white rectangle) (top). As can be seen from this figure, the measuring cell 50 can be arranged in the measuring rod 70. The capacitor plates are each connected via a coaxial line to the measuring bridge, wherein for efficient shielding of the signal, the outer conductor with the ground -. the cell body - are connected. In order to avoid an earth loop, the connection from the plates to the measuring bridge takes place only directly and thus without further contact. For this reason, an upper part of the insert was made of plastic and thus electrically isolated from the rest of the cryostat. A lower portion or lower part of the rod has special recesses, by means of which it can engage in specially provided pins in the sample space, which ensures an improved thermal coupling to the bath or the surrounding medium.

In a differential measurement method, such as the thermal expansion, both high demands are placed on the thermometry and on the thermalization of the sample directly installed in the dilatometer. Gold-plated springs 71, which are arranged with the aid of a copper block at a small distance above the cell inside the multifunctional insert (FIG. 8, top), contact an inner wall of the cooling ring channel and thus additionally support the thermal coupling of the cell 50 Placing the rod further springs 72 placed above the insert. By this it is possible to measure the temperature gradient between the upper section of the bar and to affect the pins in the desired manner. In particular, it is possible to successively attenuate the temperature gradient from the head of the rod to the pins.

To avoid or at least reduce heat input through the coaxial cables (e.g., leading from top to the measuring cell), they were wound several times around the rod.

The temperature is determined over the entire measuring range, e.g. by means of a single thermometer or thermocouple or a corresponding thermo-measuring cell. This may be, for example, a Cernox resistance thermometer from LakeShore or similar devices. As shown in Fig. 8 in the upper part, this is arranged in a preferred embodiment directly on the head of the cell in a designated bulge in close proximity to the sample. Cernox thermometers are particularly preferred since they can be used in a temperature range from 100 mK to 420 K. Thus, they can be used for many measurement applications in a very wide temperature range.

In addition to the materials already mentioned, further different materials are used in a dilatometer according to the invention. The combination of different materials leads to a background effect for the measuring cell, which can influence the measurement results. In order to keep this influence as low as possible, the other materials used are selected so that the expected influence is as small as possible. For example, sapphire washers are preferably used. As a material for insulation sheaths, for example, polyimides such as Vespel ^{® are} preferred. These are particularly suitable for extreme thermal, electrical and mechanical loads. However, other materials are conceivable as long as they can cope with the required loads.

The background effect for the measuring cell (cell effect, cell background) caused by the material combinations mentioned above is determined for the entire temperature range. The measured change in length AL _gem ^sample is the difference between the actual change in length of the sample AL ^sample and the change in length of the cell AL ^{Zel, e} .

AL _gem ^sample = AL ^sample - AL ^cell (2.7)

Since the change in length of copper has been studied extensively and is known from the literature, copper was selected as the material for determining the cell effect. loading Preferred is highly pure copper with at least 99.9% purity, preferably at least 99.99% purity, more preferably at least 99.999% purity. With a calibration sample or calibration sample, preferably of copper as described above, the cell effect can be determined by comparison with the known from the literature change in length of copper in the temperature range considered.

AL ^cell = AL _Lit ^Cu - AL _gem ^Cu (2.8) The actual sample expansion can therefore be calculated by

_AL sample _{= A} | _ _according sample. ^ Cu ₊ ^ Cu _{(2 g)}

After normalization to the sample length at room temperature L ₀ results in determining the relative extent of the sample

(AL / L ₀ ) ^sample = (1 / Lo) (AL _{according to} ^sample - AL _{according to} ^Cu ) + (AL ^c L ₀ ) _Li , (2.10)

The relative cell effect, i. the normalized to the sample length cell effect is thus given by

(AL / Lo = - (1 / Lo) AL _gem ^Cu + (AL ^c L ₀ ) _Lit (2.1 1)

The cell effect was measured by means of a calibration sample in the form of a high-purity (99.999%) copper cylinder with a length of 4 mm. After cooling, the cell was thermalized for at least three hours at a temperature of 5K. Subsequently, the sample was slowly warmed up and cooled while continuously measuring the change in length. A particularly suitable rate for the temperature change proved to be a rate of 0.3 K / min. No hysteresis was observed at this temperature change rate, indicating that the sample was in thermal equilibrium with its environment at all times. By repeating the measurements with several cycles of warming up and cooling down several times, the reproducibility of the data could be confirmed. From AL _ge m, it is possible according to formula 2.1 1 relative cell effect (AL / L ₀₎ _Ze iie to calculate. As shown in Fig. 9, cell characteristics are continuous over a large area. The course shown therefore has no (or at least no strong) kinks. This is an important prerequisite for accurate and reproducible measurement results. On the basis of the determined temperature dependence of the cell effect, the change in length of new samples can be determined in the following by means of formula 2.10.

Information about the accuracy of the measurement results is given by a test measurement on a silver sample. In Fig. 10, the change in length of a 4 mm long silver cylinder (99.999% purity) over the entire temperature range is shown in comparison to a compensation curve based on literature values of silver. The inset shows a section of the temperature range of 5 - 50 K. As you can see, the measured values agree very well with the literature values. The respective curves largely overlap.

FIG. 11 shows a comparison between measured values and literature values of the thermal expansion coefficient. Again, the good match is the

Measurements with the literature curve can be recognized throughout the entire temperature range. Even at low temperatures results in a maximum deviation of the absolute values in the order Δα = 10 ^"8 K ^" . Due to the very low expansion of ordinary metals such as copper and silver at low temperatures, the range of less than 30 K is at the limit of the very easily dissolvable change in length.

12 shows a representation of the relative error between measured values and literature values of the relative extension AL / L of a silver sample (left) and of the expansion coefficient a (right). As you can see, these are low. In the range of room temperature up to 25 K the relative error is max. 3%. Also, the maximum error of 35% at lower temperatures (<20 K) is in absolute values of the order of magnitude of

A (AL / L ₀ ) = 10 ^"7 and thus are more than an order of magnitude smaller than the length changes considered. <br/> Fig. 13 illustrates the high resolving power by means of the test measurement of copper In the diagram shown, the change in length AL (T) of the sample is included low temperatures (in this example <10 K), in which metals show a very low and linear expansion behavior, which is why the scattering of the measured values solution of the cell can be assessed. Based on the indicated error channel, a deviation of the order of 0.1 Å results.

15 shows a body (50) for a measuring cell according to the invention from various viewing angles (top right and bottom right) and schematic detail drawings. The body (50) is made of a single part, preferably milled and / or eroded. As shown in the figure, the detailed representations in the middle region of the right-hand half of the image represent enlarged representations of the representations shown on the left. The representations marked AA and BB correspond to sections along the lines marked AA or BB in the second illustration of FIG at the top of the left half of the picture. The reference numerals 1 - 33 indicate dimensions and angles, which can be adapted to the requirements. Depending on the device in which the measuring cell is to be integrated, these values can be adapted. The distances indicated by the reference numerals 1, 3, 6, 7 and 17 are independently of each other preferably between 5 and 15 mm long. The distances indicated by the reference numeral 8 are independently of each other preferably between 7.5 and 20 mm long. The distances indicated by the reference numerals 4, 20, 22, and 23 are independently of each other preferably between 2.5 and 7.5 mm long. The distances indicated by reference numerals 5, 15, 18, 19, 21, and 25 are independently of each other preferably between 0.05 and 1.5 mm long.

The width of the body is indicated by the reference numeral 16 and represents a significant size to be considered for integration into existing equipment. Preferably, the width is smaller than 50 mm, in the example shown, it is 20 mm. As can be seen in particular from the second illustration from the top on the left side, the base surface geometry of the body, whose outer surfaces (as can be seen from the illustration on the top right) essentially represent a straight cylinder, is not circular (the body is therefore no straight circular cylinder) but deviates from the circular shape. Although the base surface is essentially circular, it has two mutually opposite, parallel circular chords, which in the respective region represent the outer boundaries of the base surface. The base area corresponds in this case to a circle which is reduced on two opposite sides by, preferably equal, circular segments. The reference numerals 2, 10, 12, and 29 designate substantially circular recesses with independently selectable diameters between 1 and 5 mm. The reference numerals 9, 11, 30, 31 and 32 indicate recesses with independently selectable diameters between 7.5 and 30 mm. The indicated by the reference numerals 9, 1 1, 30 and 31 diameter are independently of each other preferably between 15 and 25 mm. Reference numerals 13, 14, 26, 27, 28 and 33 indicate angles. The angles 13, 14, 26 and 27 are independently between 25 and 115 °, the angles 26 and 27 independently preferably between 45 and 75 °. The angles 28 and 33 are independently between 90 and 150 °.

Claims

Patent claims

Miniature dilatometer for capacitive measurement of the thermal expansion and/or the magnetostriction of a sample, which can be arranged within a measuring cell of the miniature dilatometer, the miniature dilatometer being able to be arranged within a device for measuring physical properties,

characterized in that

the miniature dilatometer has a body which has a measuring cell diameter of less than 50 mm and a mass of less than 100 g.

Miniature dilatometer according to claim 1,

characterized in that

the body of the miniature dilatometer made of a material with a thermal conductivity > 200 Wm ^'1 K ^"1 and a thermal expansion coefficient

< 1710 ^"6 K ^"1 exists.

Miniature dilatometer according to claim 1 or claim 2,

characterized in that

Due to the small size and low mass of the body and/or the high thermal conductivity and/or the low coefficient of thermal expansion, the miniature dilatometer is suitable, the temperature of a measuring cell of the miniature dilatometer and the sample is at least in the range of 5 K - 200 K, preferably in the range of 10 mK - 300 K to be stabilized to ± 0.01 K and in at least this temperature range measurements of thermal expansion with a maximum sensitivity of AL/L from 0 ^"8 to 10 ^"10 , preferably AL/L from 10 ^"9 to 10 ^"10 and / or measurements of magnetostriction up to 10 Tesla or more, preferably 20 Tesla or more.

4. Miniature dilatometer according to one of the preceding claims, characterized in that

an outer surface of the body of the measuring cell essentially has the shape of a straight cylinder, wherein a lateral surface of the straight cylinder has at least two plane-parallel regions and the body has a first recess on at least one base or top surface extending in the direction of the height axis of the cylinder and having a circular cross-section at least in sections which forms a body interior.

5. Miniature dilatometer according to one of the preceding claims,

characterized in that

the body of the measuring cell has at least one first passage opening, preferably with a rectangular cross section, which is arranged in a first outer wall section of the straight cylinder and, starting from this first outer wall section, extends perpendicular to the height of the straight cylinder in the direction of the first recess, preferably up to a second outer wall section opposite the first outer wall section, preferably parallel to the plane-parallel regions of the outer wall.

6. Miniature dilatometer according to one of the preceding claims,

characterized in that

the measuring cell of the miniature dilatometer is at least partially a copper-beryllium alloy with a beryllium content of 0.5-5% by weight, preferably 1-2.5% by weight, particularly preferably 1.5-2% by weight .-%, particularly preferably 1.84% by weight.

7. Miniature dilatometer according to one of the preceding claims,

characterized in that

Changes in length of the sample to be measured, arranged in the miniature dilatometer, can be determined via a change in the electrical capacitance between two capacitor plates, preferably by means of a precision capacitance measuring bridge.

8. Miniature dilatometer according to one of the preceding claims,

characterized in that

the body of the measuring cell consists of less than 8, preferably less than 5, preferably more nger than 3 individual parts, particularly preferably only in one piece and the part / the individual parts can preferably be produced by milling and / or spark erosion.

9. Miniature dilatometer according to one of the preceding claims,

characterized in that

Ring springs, preferably leaf springs, are integrated into the body, which are preferably formed in one piece together with the body.

10. Miniature dilatometer according to one of the preceding claims,

characterized in that

the measuring cell of the miniature dilatometer has a cell diameter of less than 30 mm, particularly preferably 26 mm or less; preferably has a height of less than 50 mm, preferably less than 30 mm, preferably less than 25 mm, particularly preferably 21 mm or less and more preferably a width of less than 50 mm, preferably less than 30 mm, preferably less than 25 mm, particularly preferably 20 mm or less.

1 . Miniature dilatometer according to one of the preceding claims,

characterized in that

the measuring cell of the miniature dilatometer has a weight of less than 75 g, preferably less than 50 g, particularly preferably 42 g or less.

12. Miniature dilatometer according to one of the preceding claims,

characterized in that

the miniature dilatometer can be used in a capacity range which includes a capacity range of 1 - 250 pF, preferably 5-50 pF, preferably 20 - 25 pF.

13. Miniature dilatometer according to one of the preceding claims,

characterized in that

the measuring cell of the miniature dilatometer can be integrated into standardized measuring systems, in particular into a Physical Property Measurement System ^® from Quantum Design. Miniature dilatometer according to one of the preceding claims,

characterized in that

a thermocouple can be integrated into the body of the measuring cell or this can be arranged inside the device for measuring physical properties in the immediate vicinity of the body of the measuring cell.

Use of a miniature dilatometer according to one of the preceding claims for capacitive measurement of the thermal expansion and/or the magnetostriction of a sample.

Method for producing a miniature dilatometer,

characterized in that

the body of a measuring cell of the miniature dilatometer is composed of fewer than 5 individual parts, which are manufactured by milling and/or spark erosion.

Method for producing a miniature dilatometer according to claim 16, characterized in that

the body of the measuring cell of the miniature dilatometer consists of a single part which is manufactured by milling and/or spark erosion.

Method for producing a miniature dilatometer according to claim 16 or 17, characterized in that

a piece of material from which the body of the measuring cell of the miniature dilatometer or the parts of the body of the measuring cell of the miniature dilatometer is/are made before milling and/or spark erosion over a period of 0.5 - 48 hours at temperatures from 100 - 750 ° C, preferably over a period of 1 - 5 hours at temperatures of 250 - 500 ° C, particularly preferably over a period of 2-4 hours at temperatures of 300 - 350 ° C.