CN102931336A - Germanium telluride (GeTe) based composite thermoelectric material and preparation method thereof - Google Patents

Abstract

The invention provides a composite thermoelectric material. The chemical formula of the composite thermoelectric material is (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x , wherein the value range of x is 0.02≦x≦0.20. The invention also provides a preparation method of the composite thermoelectric material. The composite thermoelectric material provided by the invention is lead-free, has low thermal conductivity and high dimensionless figure of merit ZT, and has good thermoelectric performance.

Description

A kind of GeTe-based composite thermoelectric material and its preparation method

technical field

The invention relates to the technical field of new energy materials, in particular to a lead-free medium-temperature composite thermoelectric material and a preparation method thereof.

Background technique

Thermoelectric material is a special functional material, which can realize temperature control, temperature difference power generation and energized refrigeration by using the thermoelectric effect that produces a temperature gradient when a current passes through it, and generates an electromotive force or current when there is a temperature difference between the two ends. These refrigeration and power generation systems have the advantages of small size, light weight, no mechanical rotating parts, no noise during operation, no environmental pollution, long service life, and easy control. They are considered to be very competitive energy alternative materials in the future. It has broad application prospects in future green environmental protection energy engineering and refrigeration engineering.

The conversion efficiency of thermoelectric devices is determined by the performance of thermoelectric materials, and the performance of thermoelectric materials is measured by the dimensionless figure of merit ZT=S ² σT/k, where S is the Seebeck coefficient, σ and k are the electrical and thermal conductivity of the material, respectively, and T is the absolute temperature. A thermoelectric material with excellent performance must have high Seebeck coefficient, high electrical conductivity and low thermal conductivity.

IV-VI semiconductor thermoelectric materials, including PbTe, GeTe and PbSe are medium-temperature semiconductor thermoelectric materials, which can be used in thermoelectric power generation devices working in temperature range (400-800K), especially in the recovery of industrial waste heat and the utilization of waste heat from automobile engines. Compared with PbTe-based thermoelectric materials, GeTe thermoelectric materials do not contain Pb. Although GeTe has higher electrical conductivity, its thermal conductivity is also higher, resulting in a smaller thermoelectric figure of merit ZT.

Therefore, it is necessary to provide a composite thermoelectric material and a preparation method thereof, which does not contain lead, has low thermal conductivity, and thus can have a high dimensionless figure of merit.

Contents of the invention

The invention provides a composite thermoelectric material and a preparation method thereof.

A composite thermoelectric material, the chemical formula of the composite thermoelectric material is (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x , wherein the value range of x is 0.02≦x≦0.20.

Among them, Ag ₈ GeTe ₆ is distributed in GeTe, and x determines the phase content of Ag ₈ GeTe ₆ distributed in GeTe and the thermoelectric properties of the material.

A method for preparing the composite thermoelectric material, comprising the steps of: according to the value of x in (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x , using metal Ge, Te and Ag simple substances as raw materials, weighing the raw materials according to the proportion making GeTe-based alloys from weighed raw materials; ball-milling the GeTe-based alloys into powders, and performing spark plasma sintering on the ball-milled powders of the GeTe-based alloys to obtain the composite thermoelectric material.

The composite thermoelectric material provided by the present invention utilizes the eutectic transformation of the GeTe-Ag ₈ GeTe ₆ phase diagram to introduce a second phase of dispersedly distributed Ag ₈ GeTe ₆ into the GeTe matrix to form a composite thermoelectric material with a eutectic structure, greatly reducing The thermal conductivity of the material is improved, thereby improving its thermoelectric performance.

Description of drawings

Figure 1 is the X-ray diffraction pattern of (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x (x=0.02, 0.05 and 0.11) composite thermoelectric materials.

Figure 2 is a photo of the microstructure of (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x (x=0.11) composite thermoelectric material.

Fig. 3 is a schematic diagram of the relationship between resistivity and temperature of (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x (x=0, 0.02, 0.05, 0.08 and 0.11) composite thermoelectric materials.

Fig. 4 Schematic diagram of the relationship between Seebeck coefficient and temperature of (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x (x=0, 0.02, 0.05, 0.08 and 0.11) composite thermoelectric materials.

Fig. 5 Schematic diagram of the relationship between thermal conductivity and temperature of (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x (x=0, 0.02, 0.05, 0.08 and 0.11) composite thermoelectric materials.

Fig. 6 Schematic diagram of the relationship between dimensionless figure of merit (ZT) and temperature of (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x (x=0, 0.02, 0.05, 0.08 and 0.11) composite thermoelectric materials.

Specific implementation method

A composite thermoelectric material provided by the technical solution and its preparation method will be described in detail below with reference to the accompanying drawings.

A composite thermoelectric material, the chemical formula of the composite thermoelectric material is (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x , wherein the value range of x is 0.02≦x≦0.20, preferably 0.02≦x≦0.15.

Among them, the second phase of Ag ₈ GeTe6 is distributed in the GeTe matrix, and x determines the content of the Ag ₈ GeTe ₆ phase distributed in GeTe and the thermoelectric properties of the material.

A method for preparing the composite thermoelectric material, comprising the steps of:

In the first step, according to the value of x in (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x , metal Ge, Te and Ag simple substances are used as raw materials, and the raw materials are weighed according to the proportion;

In the second step, the weighed raw materials are made to form a GeTe-based alloy;

The third step; ball milling the GeTe-based alloy into powder;

In the fourth step, the powder obtained by ball milling the GeTe-based alloy is subjected to spark plasma sintering to obtain the composite thermoelectric material.

Wherein, in the first step, the proportions of different metals Ge, Te and Ag can be obtained according to the value of x. The value range of X is 0.02≦x≦0.20.

In the second step, the raw materials were reacted in a quartz tube at 900 degrees Celsius for 20 hours to obtain a GeTe-based alloy.

In the third step, the GeTe-based alloy can be ball-milled using a planetary ball mill.

In the fourth step, spark plasma (SPS) sintering is carried out in a vacuum environment. When the vacuum degree is 1×10 ^-2 Pa, the pressure is 30~50MPa, the sintering temperature is 600~650°C, and the holding time is 5~10 minutes. The composite thermoelectric material is obtained.

The obtained composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x is characterized by the X-ray diffraction pattern shown in FIG. 1 . Fig. 1 shows the X-ray diffraction pattern of the composite thermoelectric material when x is 0.02, 0.05 and 0.11, Fig. 2 is the microstructure photo of the composite thermoelectric material (x = 0.11), Fig. 1 and Fig. 2 show that the present invention makes The thermoelectric material contains a GeTe matrix phase and a Ag ₈ GeTe ₆ second phase.

Please refer to Figure 3, the resistivity of composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x increases with temperature. At the same temperature, the resistivity of the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x is smaller than the conductivity of GeTe at high temperature. Please refer to Figure 4, the Seebeck coefficient of the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x increases with temperature, at the same temperature, the composite thermoelectric material (GeTe) _1-x (Ag ₈ The Seebeck coefficient of GeTe ₆ ) _x is slightly smaller than that of GeTe. Referring to Figure 5, the thermal conductivity of the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x decreases with increasing temperature. Moreover, at the same temperature, the thermal conductivity of the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x is significantly lower than that of GeTe. Moreover, at the same temperature, as the value of x increases, the thermal conductivity of the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x decreases. It can be concluded from FIG. 5 that the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x can reduce the thermal conductivity of the thermoelectric material compared with GeTe. Please refer to Figure 6, the dimensionless figure of merit of the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x increases with increasing temperature. Moreover, at the same temperature, the dimensionless figure of merit of the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x is greater than that of GeTe. Moreover, at the same temperature, as the value of x increases, the dimensionless figure of merit of the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x increases. It can be concluded from Figure 6 that the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x can increase the dimensionless figure of merit of the thermoelectric material compared with GeTe, thereby increasing the thermoelectric performance of the material.

In the following, examples 1 to 3 are specifically used to illustrate the composite thermoelectric material provided by the present technology and its preparation method.

Example 1

Using Ge, Te and Ag as raw materials, weigh and proportion according to the chemical molecular formula (GeTe) _0.89 (Ag ₈ GeTe ₆ ) _0.11 and put it into a quartz tube. After vacuuming, seal and weld the quartz tube and place it in a muffle furnace Carry out reaction, reaction temperature is 900 ℃, and reaction time is 20 hours, obtains GeTe-based alloy; GeTe-based alloy obtained by reaction is ground into powder, puts into ball mill pot together with grinding ball, fills with Ar gas after pre-evacuation, A planetary ball mill was used to prepare fine powder under the protection of Ar gas. The speed of the ball mill was 200 rpm, the ball-to-material ratio was 20:1, and the ball-milling time was 8 hours. 1×10 ^-2 Pa, pressure 50MPa, sintering temperature 620°C, holding time 5 minutes, the lead-free composite thermoelectric material (GeTe) with Ag ₈ GeTe ₆ distributed in the matrix GeTe matrix is obtained. _0.89 (Ag ₈ GeTe ₆ ) _0.11 .

The phase, microstructure and thermoelectric properties of the composite thermoelectric material (GeTe) _0.89 (Ag ₈ GeTe ₆ ) _0.11 prepared in this example are shown in Figure 1-6, and its thermal conductivity is 1.23W/mK at 673K, which is Pure GeTe is 38% of 3.23W/mK at the same temperature; and its maximum figure of merit (ZT) is 1.15, which is 125% higher than pure GeTe's 0.51.

Example 2

Using Ge, Te and Ag as raw materials, weigh and proportion according to the chemical molecular formula (GeTe) _0.95 (Ag ₈ GeTe ₆ ) _0.05 and put it into a quartz tube. After vacuuming, seal and weld the quartz tube and place it in a muffle furnace Carry out reaction, reaction temperature is 900 ℃, and reaction time is 20 hours, obtains GeTe-based alloy; GeTe-based alloy obtained by reaction is ground into powder, puts into ball mill pot together with grinding ball, fills with Ar gas after pre-evacuation, A planetary ball mill was used to prepare fine powder under the protection of Ar gas. The speed of the ball mill was 200 rpm, the ball-to-material ratio was 20:1, and the ball-milling time was 8 hours. 1×10 ^-2 Pa, pressure 50MPa, sintering temperature 620°C, holding time 5 minutes, the lead-free composite thermoelectric material (GeTe) with Ag ₈ GeTe ₆ distributed in the matrix GeTe matrix can be obtained. _0.95 (Ag ₈ GeTe ₆ ) _0.05 .

The phase and thermoelectric properties of the composite thermoelectric material (GeTe) _0.95 (Ag ₈ GeTe ₆ ) _0.05 prepared in this example are shown in Figures 1 and 3-6, and its thermal conductivity is 1.98W/mK at 673K, which is pure GeTe is 61% of 3.23W/mK at the same temperature; and its maximum figure of merit (ZT) is 1.03, which is 102% higher than 0.51 of pure GeTe.

Example 3

Using Ge, Te and Ag as raw materials, weigh and proportion according to the chemical molecular formula (GeTe) _0.92 (Ag ₈ GeTe ₆ ) _0.08 and put it into a quartz tube, seal and weld the quartz tube after vacuuming and place it in a muffle furnace Carry out reaction, reaction temperature is 900 ℃, and reaction time is 20 hours, obtains GeTe-based alloy; GeTe-based alloy obtained by reaction is ground into powder, puts into ball mill pot together with grinding ball, fills with Ar gas after pre-evacuation, A planetary ball mill was used to prepare fine powder under the protection of Ar gas. The speed of the ball mill was 200 rpm, the ball-to-material ratio was 20:1, and the ball-milling time was 8 hours. 1×10 ^-2 Pa, pressure 50MPa, sintering temperature 620°C, holding time 5 minutes, the lead-free composite thermoelectric material (GeTe) with Ag ₈ GeTe ₆ distributed in the matrix GeTe matrix can be obtained. _0.92 (Ag ₈ GeTe ₆ ) _0.08 .

The phase and thermoelectric properties of the composite thermoelectric material (GeTe) _0.92 (Ag ₈ GeTe ₆ ) _0.08 prepared in this example are shown in Figures 1 and 3-6, and its thermal conductivity is 1.62W/mK at 673K, which is pure GeTe 50% of 3.23W/mK at the same temperature; and its maximum figure of merit (ZT) is 0.87, 71% higher than 0.51 of pure GeTe.

The composite thermoelectric material provided by the present invention uses the eutectic transformation of (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x to introduce a second phase of Ag ₈ GeTe ₆ dispersedly distributed in the GeTe matrix to form a composite with eutectic structure Thermoelectric materials greatly reduce the thermal conductivity of the material, thereby improving its thermoelectric performance.

Claims (6)

1. A composite thermoelectric material, the chemical formula of which is (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x , wherein the range of x is 0.02≦x≦0.20. 2. The composite thermoelectric material according to claim 1, wherein the value range of x in the chemical formula is 0.02≦x≦0.15. 3. A method for preparing the composite thermoelectric material described in claim 1 or 2, comprising the steps of: According to the value of x in (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x , metal Ge, Te and Ag simple substances are used as raw materials, and the raw materials are weighed according to the proportion; Making the weighed raw materials to form a GeTe-based alloy; ball milling the GeTe-based alloy into powder; and The powder obtained by ball milling the GeTe-based alloy is subjected to spark plasma sintering to obtain the composite thermoelectric material (GeTe) _1-x (Ag ₈ GeTe ₆ ) _x . 4. The preparation method of composite thermoelectric material as claimed in claim 3, it is characterized in that, the method that the raw material that weighs is made to form GeTe base alloy is: the described raw material that weighs is packed into quartz tube, seals after vacuumizing The quartz tube was welded and placed in a muffle furnace for reaction at a reaction temperature of 900°C and a reaction time of 20 hours to obtain a GeTe-based alloy. 5. The preparation method of composite thermoelectric material as claimed in claim 4, it is characterized in that, the method for ball milling the GeTe-based alloy into powder is: the GeTe-based alloy obtained by the reaction is ground into powder, and put into the ball mill together with the grinding balls The tank is filled with Ar gas after pre-evacuation, and the fine powder is produced by using a planetary ball mill under the protection of Ar gas. 6. the preparation method of composite thermoelectric material as claimed in claim 5 is characterized in that, the powder that described GeTe-based alloy ball milling is carried out discharge plasma sintering, obtains described composite thermoelectric material (GeTe) _1-x (Ag ₈ The GeTe ₆ ) _x method is as follows: the ball-milled powder is sintered by spark plasma (SPS) in a vacuum environment, the vacuum degree is 1×10 ^-2 Pa, the pressure is 30~50MPa, the sintering temperature is 600~650°C, and the holding time is 5 In ~10 minutes, a lead-free composite thermoelectric material in which Ag ₈ GeTe ₆ is distributed in the matrix GeTe matrix is obtained.

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