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B-Site-Ordered and Disordered Structures in A-Site-Ordered Quadruple Perovskites RMn₃Ni₂Mn₂O₁₂ with R = Nd, Sm, Gd, and Dy

Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba 305-0044, Ibaraki, Japan

Graduate School of Chemical Sciences and Engineering, Hokkaido University, North 10 West 8, Kita-ku, Sapporo 060-0810, Hokkaido, Japan

Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki 567-0047, Osaka, Japan

⁴

National Institute for Materials Science (NIMS), Sengen 1-2-1, Tsukuba 305-0047, Ibaraki, Japan

Author to whom correspondence should be addressed.

Molecules 2024, 29(23), 5488; https://doi.org/10.3390/molecules29235488

Submission received: 10 October 2024 / Revised: 15 November 2024 / Accepted: 18 November 2024 / Published: 21 November 2024

(This article belongs to the Section Inorganic Chemistry)

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Abstract

ABO₃ perovskite materials with small cations at the A site, especially with ordered cation arrangements, have attracted a lot of interest because they show unusual physical properties and deviations from general perovskite tendencies. In this work, A-site-ordered quadruple perovskites, RMn₃Ni₂Mn₂O₁₂ with R = Nd, Sm, Gd, and Dy, were synthesized by a high-pressure, high-temperature method at about 6 GPa. Annealing at about 1500 K produced samples with additional (partial) B-site ordering of Ni²⁺ and Mn⁴⁺ cations, crystallizing in space group Pn–3. Annealing at about 1700 K produced samples with disordering of Ni²⁺ and Mn⁴⁺ cations, crystallizing in space group Im–3. However, magnetic properties were nearly identical for the Pn–3 and Im–3 modifications in comparison with ferromagnetic double perovskites R₂NiMnO₆, where the degree of Ni²⁺ and Mn⁴⁺ ordering has significant effects on magnetic properties. In RMn₃Ni₂Mn₂O₁₂, one magnetic transition was found at 26 K (for R = Nd), 23 K (for R = Sm), and 22 K (for R = Gd), and two transitions were found at 10 K and 36 K for R = Dy. Curie–Weiss temperatures were close to zero in all compounds, suggesting that antiferromagnetic and ferromagnetic interactions are of the same magnitude.

Keywords:

A-site-ordered quadruple perovskites; B-site double ordering; crystal structures; structural disorder

1. Introduction

Perovskite-structure materials with a variety of cation orders attract a lot of attention, as properties can be tuned through different degrees of ordering. There are large subfamilies of perovskite-structure cation-ordered materials, for example, B-site double perovskites, A₂B′B″O₆ [1], and A-site-ordered quadruple perovskites, AA′₃B₄O₁₂ [2,3,4,5,6,7]. There are more than one thousand examples of different A₂B′B″O₆ perovskites [1] and hundreds of AA′₃B₄O₁₂ perovskites [2,3,4,5,6,7].

Among different possible combinations of B′ and B″ cations in A₂B′B″O₆, a combination of B′ = Ni²⁺ and B″ = Mn⁴⁺ attracts special attention as such a combination can produce ferromagnetic (FM) properties according to the Goodenough–Kanamori rules [8]. R₂NiMnO₆ perovskites, where R is a rare-earth element, were investigated a lot [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29], and FM properties were indeed observed for all members from R = La (T_C ≈ 280 K [10,17,19]) to R = Lu (T_C ≈ 40 K [18,19,25,26,28]). The FM Curie temperature, T_C, decreases in R₂NiMnO₆ as the deviation of the Ni–O–Mn bond angles increases from 180° [25,28]. In addition, the degree of Ni²⁺ and Mn⁴⁺ cation ordering in R₂NiMnO₆ has significant effects on the FM properties [9,18]. Near-room-temperature magnetocapacitance and magnetoresistance effects were observed in La₂NiMnO₆ [10,12,13].

The introduction of other cations [smaller than Lu³⁺ (r_XIII(Lu³⁺) = 0.977 Å [30]), such as In³⁺ with r_XIII(In³⁺) = 0.92 Å [30], Sc³⁺ with r_XIII(Sc³⁺) = 0.870 Å [30], and Mn²⁺ with r_XIII(Mn²⁺) = 0.96 Å [30])] into the A sites further reduces B–O–B′ bond angles and decreases the strength of direct B–B′ exchange interactions and can produce “exotic” properties [7,31]. For example, In₂NiMnO₆ already shows a complex incommensurate antiferromagnetic (AFM) ordering at T_N = 26 K and spin-induced ferroelectric polarization [21] in comparison with FM properties of R₂NiMnO₆. Sc₂NiMnO₆ demonstrates two AFM transitions and a complex magnetodielectric response [22]. Lu₂NiMnO₆ is located near a phase boundary, and external effects, such as moderate pressure, can induce a transition to an incommensurate AFM order from an FM order [25].

B-site double perovskites, A₂B′B″O₆, and A-site-ordered quadruple perovskites, AA′₃B₄O₁₂, can be combined to simultaneously produce A-site- and B-site-ordered structures, AA′₃B′₂B″2O₁₂ [32,33,34,35,36,37,38,39,40,41,42,43,44,45,46]. Depending on the combinations of B′ and B″ cations, such AA′₃B’₂B″2O₁₂ perovskites can show large ferrimagnetic transitions above room temperature [35,37] and half-metallic properties [37,41]. In addition, such perovskites can show good catalytic properties [4], as they contain transition metals in different oxidation states and exotic magnetic ground states [28].

The R₂NiMnO₆ family of double perovskites was recently extended further through the synthesis of an AA′₃B′₂B″2O₁₂-type perovskite, LaMn₃Ni₂Mn₂O₁₂ [28]. The average size of La³⁺ and 3Mn³⁺ cations is small; therefore, LaMn₃Ni₂Mn₂O₁₂ falls into the region with “exotic” properties, as Ni–O–Mn bond angles deviate significantly from 180° [28]. Two magnetic transitions were found in LaMn₃Ni₂Mn₂O₁₂ in comparison with other members of the R₂NiMnO₆ family (R = La–Lu), and complex magnetic structures were realized [28,29].

In this work, we prepared and investigated other members of RMn₃Ni₂Mn₂O₁₂ perovskites with R = Nd, Sm, Gd, and Dy, where the average size of R³⁺ and 3Mn³⁺ cations is further reduced (Table 1). In addition, we prepared two modifications of RMn₃Ni₂Mn₂O₁₂ perovskites with R = Nd and Sm, one with B-site ordering and the second without B-site ordering, and investigated the effects of B-site ordering on magnetic properties.

2. Results and Discussion

RMn₃Ni₂Mn₂O₁₂ samples with R = Nd, Sm, Gd, and Dy prepared at 1500 K crystallized in space group Pn–3 because of the observation of a (311) reflection on synchrotron XRPD data (Figure 1). The Pn–3 structure has two B sites and corresponds to an ordered arrangement of Ni²⁺ and Mn⁴⁺ cations (or at least partial ordering). The distribution of Ni²⁺ and Mn⁴⁺ cations between the two sites was refined with constraints on the full site occupation and the total chemical compositions. All the samples showed nearly the same refined occupation factors of 0.8Ni²⁺ + 0.2Mn⁴⁺ for the B site and 0.2Ni²⁺ + 0.8Mn⁴⁺ for the B′ site, suggesting a significant degree of Ni²⁺ and Mn⁴⁺ ordering. We also checked the occupation factors (g) of the R site and found that it was very close to 1 (g(Nd) = 1.0013(12), g(Sm) = 0.9994(11), g(Gd) = 1.0057(13), and g(Dy) = 1.0026(11)). Therefore, the occupation factor of the R site was fixed at 1 in the final models. All the samples contained a small amount of NiO impurity; the appearance of NiO impurity was also observed in LaMn₃Ni₂Mn₂O₁₂ [28]. The refined structural parameters and primary bond lengths for RMn₃Ni₂Mn₂O₁₂-Pn–3 are summarized in Table 2 and Table 3. Experimental, calculated, and difference synchrotron XRPD patterns are shown in Figure 1 for NdMn₃Ni₂Mn₂O₁₂-Pn–3 as an example.

The accuracy of determination of distributions of Ni²⁺ and Mn⁴⁺ cations with synchrotron XRPD is, of course, much lower than with neutron diffraction [28]. Nevertheless, with the obtained distributions of Ni²⁺ and Mn⁴⁺ cations, the refined isotropic atomic displacement parameters of the Ni₁ and Mn₂ sites were almost comparable to each other (about 0.4 Å²) for all compounds. On the other hand, the refined isotropic atomic displacement parameters were quite different for two extreme distributions of Ni²⁺ and Mn⁴⁺ cations: B(Ni₁) = 0.78(3) Å² and B(Mn₂) = −0.05(2) Å² for the full cation ordering and B(Ni₁) = 0.11(2) Å² and B(Mn₂) = 0.65(3) Å² for the full cation disordering (for the R = Nd sample as an example).

RMn₃Ni₂Mn₂O₁₂ samples with R = Nd and Sm prepared at 1700 K crystallized in space group Im–3 because of the absence of a (311) reflection on synchrotron XRPD data (Figure 2). The Im–3 structure has one B site and, therefore, corresponds to a disordered arrangement of Ni²⁺ and Mn⁴⁺ cations. The refined structural parameters and primary bond lengths for RMn₃Ni₂Mn₂O₁₂-Im–3 are summarized in Table 4. Experimental, calculated, and difference synchrotron XRPD patterns are shown in Figure 2 for NdMn₃Ni₂Mn₂O₁₂-Im–3 as an example. RMn₃Ni₂Mn₂O₁₂ samples with R = Nd and Sm prepared at 1700 K crystallized in space group Im–3 because of the absence of a (311) reflection on synchrotron XRPD data (Figure 2). The Im–3 structure has one B site and, therefore, corresponds to the disordered arrangement of Ni²⁺ and Mn⁴⁺ cations. Experimental, calculated, and difference synchrotron XRPD patterns are shown in Figure 2 for NdMn₃Ni₂Mn₂O₁₂-Im–3 as an example.

Figure 3 shows lattice parameters as a function of the ionic radius [30] for RMn₃Ni₂Mn₂O₁₂ samples with R = La [28], Nd, Sm, Gd, and Dy. Nearly linear behavior of the cubic lattice parameter was observed. Figure 3 also shows R–O bond lengths and bond valence sum (BVS) values [47] as a function of the ionic radius. The BVS values of Mn³⁺, Mn⁴⁺, and Ni²⁺ sites/cations were almost constant in all RMn₃Ni₂Mn₂O₁₂-Pn–3 compounds independent of the R³⁺ cations and agreed well with the expected formal oxidation states. On the other hand, the R–O bond length and the BVS values of the R sites changed monotonically and noticeably, and they were dependent on the R³⁺ cations. In LaMn₃Ni₂Mn₂O₁₂ [28], the BVS value of the La site was +3.40, indicating that La³⁺ is highly overbonded (probably for this reason, the BVS value of the La site was not mentioned and discussed in [28]). In DyMn₃Ni₂Mn₂O₁₂, the BVS value of the Dy site was +2.72, indicating that Dy³⁺ is noticeably underbonded. The optimal BVS value of +3.0 is realized in SmMn₃Ni₂Mn₂O₁₂. Severe underbonding of R³⁺ could be a reason why RMn₃Ni₂Mn₂O₁₂ with smaller R³⁺ cations (R = Er and Tm) could not be prepared.

Magnetic properties of NdMn₃Ni₂Mn₂O₁₂ and SmMn₃Ni₂Mn₂O₁₂ compounds in two modifications (Pn–3 and Im–3) are shown in Figure 4 and Figure 5 (also marked by the synthesis temperatures between 1500 K and 1700 K). Temperature-dependent magnetic properties were almost identical for the two modifications. Magnetic properties of GdMn₃Ni₂Mn₂O₁₂ and DyMn₃Ni₂Mn₂O₁₂ compounds (the Pn–3 modification) are shown in Figure 6 and Figure 7; they were dominated by large moments of Gd³⁺ and Dy³⁺ cations. Nevertheless, differential dχ/dT versus T curves allowed the detection of one magnetic anomaly in GdMn₃Ni₂Mn₂O₁₂ and two magnetic anomalies in DyMn₃Ni₂Mn₂O₁₂. At high temperatures, inverse magnetic susceptibilities followed the Curie–Weiss law (see Figure 7 as an example), and we obtained Curie–Weiss fitting parameters using the 10 kOe FCC curves in a temperature range of 200–350 K. The Curie–Weiss fitting parameters are summarized in Table 5. The experimental effective magnetic moments (μ_eff) were close to the expected calculated values (μ_calc). It is interesting that the Curie–Weiss temperatures (θ) were very small, suggesting that antiferromagnetic and ferromagnetic interactions are of the same magnitude and nearly cancel each other. In GdMn₃Ni₂Mn₂O₁₂ and DyMn₃Ni₂Mn₂O₁₂ compounds, the Curie–Weiss temperatures were slightly positive, suggesting that ferromagnetic interactions are slightly stronger. Unfortunately, no Curie–Weiss fits were reported for LaMn₃Ni₂Mn₂O₁₂ [28] to compare with our data. It is possible that a similar “strange” Curie–Weiss temperature was obtained; therefore, such data were not mentioned and discussed. In all R₂NiMnO₆ (R = La–Lu [10,16,17,18,19]), Tl₂NiMnO₆ [23], and In₂NiMnO₆ [20], positive and large Curie–Weiss temperatures were found indicating that ferromagnetic interactions are dominant. On the other hand, in Sc₂NiMnO₆ [22], a negative Curie–Weiss temperature of about −60 K was observed, indicating that antiferromagnetic interactions are dominant. Therefore, there could be strong competition of different magnetic interactions in RMn₃Ni₂Mn₂O_12, resulting in nearly zero Curie–Weiss temperatures.

Isothermal magnetization curves (M versus H) of NdMn₃Ni₂Mn₂O₁₂ and SmMn₃Ni₂Mn₂O₁₂ compounds in two modifications (Pn–3 and Im–3) are shown in Figure 8. Again, M versus H curves were almost identical for the two modifications. Small hysteresis near the origin was found, but no saturation behavior was observed. M versus H curves of GdMn₃Ni₂Mn₂O₁₂ and DyMn₃Ni₂Mn₂O₁₂ compounds (Pn–3 modifications) are shown in Figure 9; small hysteresis near the origin was observed in GdMn₃Ni₂Mn₂O₁₂, while no hysteresis was detected in DyMn₃Ni₂Mn₂O₁₂. The M versus H curves of DyMn₃Ni₂Mn₂O₁₂ were mainly determined by properties of Dy³⁺ cations and suggest the absence of any ferromagnetic-like contributions. Except for a very weak, extended hysteresis in SmMn₃Ni₂Mn₂O₁₂, its M versus H curve also suggests the absence of any significant ferromagnetic-like contributions. On the other hand, M versus H curves of NdMn₃Ni₂Mn₂O₁₂ and GdMn₃Ni₂Mn₂O₁₂ were similar to those of LaMn₃Ni₂Mn₂O₁₂ [28] and suggest the presence of ferromagnetic-like contributions.

Specific heat data for two modifications of SmMn₃Ni₂Mn₂O₁₂ were measured (Figure 10b), and almost no difference was observed. Specific heat data for the Pn–3 modification of other compounds (R = Nd, Gd, and Dy) are shown in Figure 10. Specific heat measurements confirmed one clear magnetic transition in the samples with R = Nd, Sm, and Gd and two clear magnetic transitions in the sample with R = Dy in agreement with the χ versus T measurements. In the case of LaMn₃Ni₂Mn₂O₁₂ [28], specific heat measurements could detect two magnetic transitions at 34 K and 46 K, where the transition at 46 K was assigned to a long-range ordering of Mn³⁺ cations at the square-planar A′ sites, and the transition at 34 K was assigned to a long-range ordering of Ni²⁺ and Mn⁴⁺. Transition temperatures found in R = Nd, Sm, and Gd were noticeably smaller than those of R = La. Therefore, it is possible that the size of R³⁺ cations plays an important role and can move the systems into different ground states. Another possibility is that the degree of Ni²⁺ and Mn⁴⁺ cation ordering plays an important role and determines magnetic transition temperatures.

To get a deeper understanding of magnetic behavior, we measured ac magnetic susceptibility curves of the Pn–3 modification of NdMn₃Ni₂Mn₂O₁₂ as an example (Figure 11). Small frequency dependence in the χ″ peak intensities was observed; however, peak positions in temperature were almost independent of frequency, suggesting that there are no spin-glass-like contributions. No dependence on the applied H_ac field of 0.05, 0.5, and 5 Oe (inset of Figure 11) was also observed on both the χ′ versus T and the χ″ versus T curves. Peaks on the χ′ versus T curves were observed near 14 K, while peaks on the χ″ versus T curves were observed near 9 K. Both temperatures were different from peak positions on the dc dχT/dT versus T curves, but peaks on the χ′ versus T curves basically matched with the peak on the ZFC dc χ versus T curve measured at a small magnetic field of H = 100 Oe (Figure 4b).

Considering the presence of spin-induced ferroelectric properties in In₂NiMnO₆ [21] and complex magnetodielectric effects in Sc₂NiMnO₆ [22], we checked the presence or absence of magnetodielectric effects in such RMn₃Ni₂Mn₂O₁₂ perovskites selecting the Pn–3 modification of NdMn₃Ni₂Mn₂O₁₂ as an example (Figure 12). However, no dielectric anomalies were observed near the magnetic transition temperature. The dielectric constant showed a sharp increase above about 50 K (at 100 Hz) with characteristic frequency-dependent peaks on the loss tangent. These features correspond to increased conductivity and Maxwell–Wagner contributions. Therefore, NdMn₃Ni₂Mn₂O₁₂ perovskite does not show magnetodielectric effects and magnetic-transition-induced ferroelectric polarization.

In the case of double perovskites R₂NiMnO₆ with ferromagnetic ground states, the degree of ordering of Ni²⁺ and Mn⁴⁺ cations has significant effects on magnetic properties, especially on the saturation magnetization on M versus H curves, where a full ordering of Ni²⁺ and Mn⁴⁺ cations should give the magnetization of about 5μ_B/f.u. [10]. Deviations of the saturation magnetization from 5μ_B/f.u. can give information about the degree of Ni²⁺ and Mn⁴⁺ disordering. On the other hand, we found that the saturation magnetization on the M versus H curves of RMn₃Ni₂Mn₂O₁₂ (and other magnetic properties) was almost independent of the degree of Ni²⁺ and Mn⁴⁺ disordering. This fact suggests that different magnetic ground states could be realized in all RMn₃Ni₂Mn₂O₁₂ in comparison with R₂NiMnO₆, and magnetic structures of RMn₃Ni₂Mn₂O₁₂ should be studied with neutron diffraction in future works. Magnetic transition temperatures and properties did not show any clear systematic trends as a function of the ionic radius of R³⁺ cations in RMn₃Ni₂Mn₂O₁₂. On the other hand, in R₂NiMnO₆ perovskites, magnetic transition temperatures show a clear and sharp decrease with decreasing the ionic radius of R³⁺ cations [18,19,25,28].

Effects of the synthesis conditions on the degree of B-site cation ordering were observed before, for example, in La₂NiMnO₆ [9], Tl₂NiMnO₆ [23], and CaCu₃Fe₂Os₂O₁₂ [36], where higher-temperature annealing (at high pressures) usually results in B-site cation disordering. Our results on RMn₃Ni₂Mn₂O₁₂ are consistent with the tendencies observed in the literature.

3. Materials and Methods

RMn₃Ni₂Mn₂O₁₂ samples with R = Nd, Sm, Gd, and Dy were prepared from stoichiometric mixtures of R₂O₃ (Rare Metallic Co., Tokyo, Japan, 99.9%), Mn₂O₃, single-phase and stoichiometric MnO₂ (Alfa Aesar, Waltham, MA, USA, 99.9%), and NiO (Rare Metallic Co., Tokyo, Japan, 99.9%). Single-phase Mn₂O₃ was prepared from a commercial MnO₂ chemical (Rare Metallic Co., Tokyo, Japan, 99.99%) by annealing in air at 923 K for 24 h. The synthesis was performed at about 6 GPa and at about 1500 K for 2 h in sealed Au capsules and at about 1700 K for 2 h in sealed Pt capsules using a belt-type HP instrument. After annealing at high temperatures, the samples were cooled down to room temperature by turning off the heating current, and the pressure was slowly released. We note that we also tried to prepare RMn₃Ni₂Mn₂O₁₂ samples with smaller R³⁺ cations, such as R = Er and Tm (at 6 GPa and 1500 K). However, the samples contained a lot of impurities. The R = Er sample (with a = 7.3189 Å) had ErMn₂O₅ (9.5 wt. %), NiO (9.2 wt. %), and a corundum-structure impurity (2.4 wt. %). The R = Tm sample (with a = 7.3190 Å) had TmMn₂O₅ (15.7 wt. %), NiO (8.2 wt. %), and a corundum-structure impurity (6.1 wt. %). The presence of large amounts of impurities suggests that the chemical compositions of the main phases significantly shifted from the target composition.

X-ray powder diffraction (XRPD) data were collected at room temperature on a MiniFlex600 diffractometer (Rigaku, Tokyo, Japan) using CuKα radiation (2θ range of 8–100°, a step width of 0.02°, and scan speed of 2°/min). Room-temperature synchrotron XRPD data were measured on the BL15XU beamline (the former NIMS beamline) of SPring-8 (Hyogo, Japan) [48] between 2.04° and 60.23° at 0.003° intervals in 2θ with the wavelength of λ = 0.65298 Å. The samples were placed into open Lindemann glass capillary tubes (inner diameter: 0.1 mm), which were rotated during measurements. The Rietveld analysis of all XRPD data was performed using the RIETAN-2000 program [49].

Magnetic measurements were performed on SQUID magnetometers (Quantum Design MPMS-7T and MPMS3, San Diego, CA, USA) between 2 and 300 K (or 400 K) in applied fields of 100 Oe and 10 kOe under both zero-field-cooled (ZFC) and field-cooled on cooling (FCC) conditions. Magnetic-field dependence was measured at different temperatures between −70 and 70 kOe. Frequency-dependent alternating current (ac) susceptibility measurements were performed on cooling with an MPMS-1T instrument Quantum Design, San Diego, CA, USA) at different frequencies (f), different applied oscillating magnetic fields (H_ac), and zero static dc field (H_dc = 0 Oe).

Specific heat, C_p, was measured on cooling from 270 K to 2 K at zero magnetic field and from 100 K to 2 K at a magnetic field of 90 kOe by a pulse relaxation method using a commercial calorimeter (Quantum Design PPMS, San Diego, CA, USA). All magnetic and specific heat measurements were performed using pieces of pellets.

Dielectric properties were measured using an Alpha-A High-Performance Frequency Analyzer (NOVOCONTROL Technologies, Montabaur, Germany) on cooling and heating in a temperature range between 3 K and 300 K and a frequency range from 100 Hz to 665 kHz at a zero magnetic field. The cooling–heating rate was 2 K/min between 70 K and 300 K and 0.5 K/min between 3 K and 70 K.

Scanning electron microscopy (SEM) images were obtained on a Miniscope TM3000 operating at 15 kV (Hitachi, Tokyo, Japan).

4. Conclusions

A-site-ordered quadruple perovskites, RMn₃Ni₂Mn₂O₁₂ with R = Nd, Sm, Gd, and Dy, were synthesized by a high-pressure, high-temperature method at about 6 GPa in two modifications. Annealing at a lower temperature of about 1500 K favors a (partial) B-site ordering, while annealing at a higher temperature of about 1700 K gives a disordered arrangement of Ni²⁺ and Mn⁴⁺ cations. The B-site-ordered structure has space group Pn–3, while the B-site-disordered structure has space group Im–3. However, magnetic properties were nearly identical for the Pn–3 and Im–3 modifications in comparison with ferromagnetic double perovskites R₂NiMnO₆. RMn₃Ni₂Mn₂O₁₂ samples show one magnetic transition at 26 K for R = Nd, 23 K for R = Sm, and 22 K for R = Gd, as well as two magnetic transitions at 10 K and 36 K for R = Dy. Curie–Weiss temperatures were close to zero in all compounds, suggesting that antiferromagnetic and ferromagnetic interactions are of the same magnitude.

Author Contributions

Conceptualization, A.A.B.; methodology, A.A.B.; validation, A.A.B.; formal analysis, A.A.B.; investigation, A.A.B., R.L., M.T. and K.Y.; resources, K.Y.; data curation, A.A.B.; writing—original draft preparation, A.A.B.; writing—review and editing, A.A.B.; supervision, A.A.B. and K.Y.; project administration, A.A.B.; funding acquisition, K.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was partially supported by a Grant-in-Aid for Scientific Research (No. JP22H04601) from the Japan Society for the Promotion of Science and the Kazuchika Okura Memorial Foundation (No. 2022-11).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the author upon request.

Acknowledgments

The synchrotron radiation experiments were conducted at the former NIMS beamline (BL15XU) of SPring-8 with the approval of the former NIMS Synchrotron X-ray Station (proposal numbers: 2019A4501, 2019B4500, and 2020A4501). We thank Y. Katsuya for his help at SPring-8. MANA was supported by the World Premier International Research Center Initiative (WPI), MEXT, Japan.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Experimental (black crosses), calculated (red line), and difference (blue line at the bottom) room-temperature synchrotron X-ray powder diffraction patterns of NdMn₃Ni₂Mn₂O₁₂ (in the Pn–3 modification, prepared at 1500 K) in a 2θ range of 6° and 59°. The tick marks show possible Bragg reflection positions for the main phase and NiO impurity (from top to bottom). Inset shows a zoomed part in a 2θ range of 16° and 17.8° and emphasizes the presence of the (311) reflection from the B-site ordering. Inset shows a scanning electron microscopy (SEM) image, where the scale bar is 20 µm.

Figure 2. Experimental (black crosses), calculated (red line), and difference (blue line at the bottom) room-temperature synchrotron X-ray powder diffraction patterns of NdMn₃Ni₂Mn₂O₁₂ (in the Im–3 modification, prepared at 1700 K) in a 2θ range of 6° and 59°. The tick marks show possible Bragg reflection positions for the main phase and NiO impurity. Inset shows a zoomed part in a 2θ range of 16° and 17.9° and emphasizes the absence of the (311) reflection and the absence of B-site ordering.

Figure 3. (a) The room-temperature cubic lattice parameter in RMn₃Ni₂Mn₂O₁₂ (R = La [28], Nd, Sm, Gd, and Dy) as a function of the ionic radius R³⁺ (for the coordination number 8 as ionic radii for the coordination number XII are not available for small R³⁺ cations (R = Gd and Dy) [30]). NPD: from neutron powder diffraction. XRD: from X-ray powder diffraction. (b) R–O bond length (the left-hand axis) and bond-valence sum for R³⁺ (the right-hand axis) in RMn₃Ni₂Mn₂O₁₂ (R = La [28], Nd, Sm, Gd, and Dy) as a function of the ionic radius R³⁺.

Figure 4. (a) ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves (χ = M/H) of two modifications of NdMn₃Ni₂Mn₂O₁₂ (the Pn–3 modification, prepared at 1500 K, and the Im–3 modification, prepared at 1700 K) measured at H = 10 kOe. The inset shows the dχT/dT versus T curves (all). (b) ZFC and FCC curves of two modifications of NdMn₃Ni₂Mn₂O₁₂ measured at H = 100 Oe. The inset shows the FCC dχT/dT versus T curves.

Figure 5. (a) ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves (χ = M/H) of two modifications of SmMn₃Ni₂Mn₂O₁₂ (the Pn–3 modification, prepared at 1500 K, and the Im–3 modification, prepared at 1700 K) measured at H = 10 kOe. The inset shows FCC dχT/dT versus T curves. (b) ZFC and FCC curves of two modifications of SmMn₃Ni₂Mn₂O₁₂ measured at H = 100 Oe.

Figure 6. ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves (χ = M/H) of GdMn₃Ni₂Mn₂O₁₂ (the Pn–3 modification, prepared at 1500 K) measured at H = 10 kOe. The first inset shows ZFC and FCC curves of GdMn₃Ni₂Mn₂O₁₂ measured at H = 100 Oe. The second inset shows the FCC dχ/dT versus T curves.

Figure 7. ZFC (filled symbols) and FCC (empty symbols) dc magnetic susceptibility curves (χ = M/H) of DyMn₃Ni₂Mn₂O₁₂ (the Pn–3 modification, prepared at 1500 K) measured at H = 10 kOe (the left-hand axis). The right-hand axis shows the FCC χ⁻¹ versus T curve with the Curie–Weiss fit (black line). The fitting parameters are given in the figure. The inset shows dχ/dT versus T curves.

Figure 8. M versus H curves of two modifications of RMn₃Ni₂Mn₂O₁₂ (the Pn–3 modification, prepared at 1500 K, and the Im–3 modification, prepared at 1700 K) measured at T = 5 K with (a) R = Nd and (b) R = Sm. The insets show zoomed parts near the origin.

Figure 9. M versus H curves of GdMn₃Ni₂Mn₂O₁₂ and DyMn₃Ni₂Mn₂O₁₂ (the Pn–3 modification, prepared at 1500 K) measured at T = 5 K. The inset shows zoomed parts near the origin.

Figure 10. C_p/T versus T curves of RMn₃Ni₂Mn₂O₁₂ measured at H = 0 (black curves) and 90 kOe (red curves) for (a) R = Nd (the Pn–3 modification), (b) R = Sm (the Pn–3 modification and the Im–3 modification (blue and brown curves)), (c) R = Gd (the Pn–3 modification), and (d) R = Dy (the Pn–3 modification). Arrows show magnetic transition temperatures. Data below 100 K are shown; inset on panel (a) shows full data up to 270 K (at H = 0 Oe).

Figure 11. (a) Real χ′ versus T and (b) imaginary χ″ versus T curves of NdMn₃Ni₂Mn₂O₁₂ (the Pn–3 modification) at different frequencies (f). Inset shows the χ′ versus T curves at different H_ac (H_ac = 0.05, 0.5, and 5 Oe) and one frequency (f = 300 Hz).

Figure 12. Temperature dependence of (a) dielectric constant and (b) loss tangent at different frequencies (f: indicated on the figure) in NdMn₃Ni₂Mn₂O₁₂ (the Pn–3 modification) at H = 0 Oe. Inset shows frequency dependence of peak positions on loss tangent as T_max versus log(f) (black circles with line) and 1000/T_max versus log(f) (red squares with line).

Table 1. A list of RMn₃Ni₂Mn₂O₁₂ samples prepared (at a high pressure of 6 GPa) and investigated in this work.

R	Synthesis Temperature	Symmetry
Nd	1500 K	Pn–3
Nd	1700 K	Im–3
Sm	1500 K	Pn–3
Sm	1700 K	Im–3
Gd	1500 K	Pn–3
Dy	1500 K	Pn–3

Table 2. Structure parameters of RMn₃Ni₂Mn₂O₁₂ (Pn–3; prepared at 1500 K) at room temperature from synchrotron powder X-ray diffraction data.

R	Nd	Sm	Gd	Dy
a (Å)	7.35504(1)	7.34371(1)	7.33561(1)	7.32757(1)
V (Å³)	397.8824(2)	396.0468(5)	394.7375(5)	393.4419(4)
B_iso(R) (Å²)	0.436(5)	0.532(5)	0.551(6)	0.661(5)
B_iso(Mn_SQ) (Å²)	0.541(9)	0.578(8)	0.560(9)	0.550(7)
g(Ni₁/Mn₁)	0.82(2)Ni+ 0.18Mn	0.834(17)Ni+ 0.166Mn	0.82(2)Ni+ 0.18Mn	0.831(16)Ni+ 0.169Mn
B_iso(Ni₁/Mn₁) (Å²)	0.36(4)	0.42(4)	0.34(4)	0.38(3)
g(Mn₂/Ni₂)	0.82Mn+ 0.18Ni	0.834Mn+ 0.166Ni	0.82Mn+ 0.18Ni	0.831Mn+ 0.169Ni
B_iso(Mn₂/Ni₂) (Å²)	0.38(4)	0.36(4)	0.45(4)	0.34(4)
x(O)	0.2576(5)	0.2576(5)	0.2576(6)	0.2574(5)
y(O)	0.42527(16)	0.42542(16)	0.42462(19)	0.42412(16)
z(O)	0.55854(15)	0.55767(14)	0.55771(17)	0.55632(14)
B_iso(O) (Å²)	0.49(3)	0.62(3)	0.54(3)	0.60(3)
R_wp (%)	3.66	4.17	4.66	4.85
R_p (%)	2.40	2.78	2.87	3.32
R_p (%)	1.89	2.44	1.94	2.26
R_F (%)	2.42	3.02	2.55	3.13
Impurities:
NiO (R–3m)	3.0 wt. %	2.8 wt. %	1.5 wt. %	1.8 wt. %
GdFeO₃-related	–	0.5 wt. %	2.0 wt. %	1.7 wt. %

Space group Pn–3 (No. 201, setting 2); Z = 2. Fractional coordinates: R: 2a (0.25, 0.25, 0.25), Mn_SQ: 6d (0.25, 0.75, 0.75), Ni₁/Mn₁: 4b (0, 0, 0), Mn₂/Ni₂: 4c (0.5, 0.5, 0.5), and O: 24h (x, y, z). Occupation factors, g, of the R, Mn_SQ, O sites are 1. Constraints on occupation factors: g(Mn₁) = g(Ni₂) = 1 − g(Ni₁) and g(Mn₂) = g(Ni₁). GdFeO₃-related impurities: for R = Sm, space group Pnma, a = 5.5165 Å, b = 7.6078 Å, c = 5.3470 Å; for R = Gd, space group P2₁/n, a = 5.2908 Å, b = 5.5452 Å, c = 7.5560 Å, β = 90.1356°; for R = Dy, space group P2₁/n, a = 5.2452 Å, b = 5.5423 Å, c = 7.4960 Å, β = 90.2082°.

Table 3. Bond lengths (in Å), bond valence sums (BVS), and Ni–O–Mn bond angles (in deg) in RMn₃Ni₂Mn₂O₁₂ (Pn–3; prepared at 1500 K) at room temperature from synchrotron powder X-ray diffraction data.

R	Nd	Sm	Gd	Dy
R–O × 12 (Å)	2.6105(11)	2.6015(11)	2.5959(13)	2.5824(11)
BVS(R³⁺)	3.16	3.00	2.86	2.74
Mn_SQ–O × 4 (Å)	1.9099(11)	1.9125(11)	1.9062(14)	1.9091(11)
Mn_SQ–O × 4 (Å)	2.7732(12)	2.7712(11)	2.7731(14)	2.7784(11)
BVS(Mn³⁺)	2.93	2.91	2.95	2.93
Ni₁/Mn₁–O × 6 (Å)	2.019(4)	2.014(3)	2.014(4)	2.009(3)
BVS(Ni²⁺)	2.24	2.27	2.27	2.30
Mn₂/Ni₂–O × 6 (Å)	1.915(4)	1.910(3)	1.910(4)	1.908(3)
BVS(Mn⁴⁺)	3.87	3.92	3.93	3.95
Ni₁–O–Mn₂	138.38(6)	138.65(6)	138.38(8)	138.56(6)

Table 4. Structure parameters, bond lengths, and bond valence sums (BVSs) of RMn₃Ni₂Mn₂O₁₂ (Im–3; prepared at 1700 K) at room temperature from synchrotron powder X-ray diffraction data.

R	Nd	Sm
a (Å)	7.35677(1)	7.34621(1)
V (Å³)	398.1629(5)	396.4512(5)
B_iso(R) (Å²)	0.382(5)	0.285(5)
B_iso(Mn_SQ) (Å²)	0.558(9)	0.413(8)
B_iso(Ni/Mn) (Å²)	0.297(7)	0.228(6)
x(O)	0.30930(16)	0.30505(15)
y(O)	0.17406(18)	0.17617(17)
B_iso(O) (Å²)	0.63(3)	0.10(2)
R_wp (%)	4.46	5.56
R_p (%)	2.89	3.59
R_p (%)	3.88	3.70
R_F (%)	3.90	3.57
Impurities:
NiO (R–3m)	2.9 wt. %	4.1 wt. %
R–O × 12 (Å)	2.6110(12)	2.5879(11)
BVS(R³⁺)	3.16	3.11
Mn_SQ–O × 4 (Å)	1.8994(12)	1.9303(12)
Mn_SQ–O × 4 (Å)	2.7781(13)	2.7767(12)
BVS(Mn³⁺)	3.00	2.78
Ni/Mn–O × 6 (Å)	1.9711(4)	1.9572(4)
BVS(Ni²⁺/Mn⁴⁺)	2.91	3.02
Ni/Mn–O–Ni/Mn	137.85(7)	139.56(7)

Space group Im–3 (No. 204); Z = 2. Fractional coordinates: R: 2a (0, 0, 0), Mn_SQ: 6b (0, 0.5, 0.5), Ni/Mn: 8c (0.25, 0.25, 0.25), and O: 24g (x, y, 0). Occupation factors, g, of the R, Mn_SQ, O sites are 1. The occupation of the Ni/Mn site was fixed at 0.5Ni + 0.5Mn. For BVS of Ni²⁺/Mn⁴⁺, an average R₀ value between R₀(Ni²⁺) = 1.654 and R₀(Mn⁴⁺) = 1.753 was used [47].

Table 5. Temperatures of magnetic anomalies and parameters of the Curie–Weiss fits and M versus H curves at T = 5 K for RMn₃Ni₂Mn₂O₁₂.

R	T_N (K)	μ_eff (μ_B/f.u.)	μ_calc (μ_B/f.u.)	θ (K)	M_S (μ_B/f.u.)
Nd (Pn–3)	26	11.08(2)	11.413	−1.7(1.0)	6.90
Nd (Im–3)	26	11.211(13)	11.413	−0.9(7)	7.04
Sm (Pn–3)	23	10.704(9)	10.966	−0.2(5)	4.70
Sm (Im–3)	23	10.842(9)	10.966	−2.7(5)	4.70
Gd (Pn–3)	22	13.383(7)	13.491	+8.4(3)	10.70
Dy (Pn–3)	10, 36	14.886(17)	15.178	+2.8(6)	11.36

The Curie–Weiss fits are performed between 200 and 350 K using the FCC χ ⁻¹ versus T data at 10 kOe. M_S is the magnetization value at T = 5 K and H = 70 kOe. μ_calc is calculated using 3.5μ_B for Nd³⁺, 1.5μ_B for Sm³⁺, 8.0μ_B for Gd³⁺, 10.6μ_B for Dy³⁺, 4.899μ_B for Mn³⁺, 2.828μ_B for Ni²⁺, and 3.873μ_B for Mn⁴⁺. T_N values were determined from peaks on the 10 kOe FCC d(χT)/dT versus T or dχ/dT versus T curves.

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Belik, A.A.; Liu, R.; Tanaka, M.; Yamaura, K. B-Site-Ordered and Disordered Structures in A-Site-Ordered Quadruple Perovskites RMn₃Ni₂Mn₂O₁₂ with R = Nd, Sm, Gd, and Dy. Molecules 2024, 29, 5488. https://doi.org/10.3390/molecules29235488

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Belik AA, Liu R, Tanaka M, Yamaura K. B-Site-Ordered and Disordered Structures in A-Site-Ordered Quadruple Perovskites RMn₃Ni₂Mn₂O₁₂ with R = Nd, Sm, Gd, and Dy. Molecules. 2024; 29(23):5488. https://doi.org/10.3390/molecules29235488

Chicago/Turabian Style

Belik, Alexei A., Ran Liu, Masahiko Tanaka, and Kazunari Yamaura. 2024. "B-Site-Ordered and Disordered Structures in A-Site-Ordered Quadruple Perovskites RMn₃Ni₂Mn₂O₁₂ with R = Nd, Sm, Gd, and Dy" Molecules 29, no. 23: 5488. https://doi.org/10.3390/molecules29235488

APA Style

Belik, A. A., Liu, R., Tanaka, M., & Yamaura, K. (2024). B-Site-Ordered and Disordered Structures in A-Site-Ordered Quadruple Perovskites RMn₃Ni₂Mn₂O₁₂ with R = Nd, Sm, Gd, and Dy. Molecules, 29(23), 5488. https://doi.org/10.3390/molecules29235488

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B-Site-Ordered and Disordered Structures in A-Site-Ordered Quadruple Perovskites RMn₃Ni₂Mn₂O₁₂ with R = Nd, Sm, Gd, and Dy

Abstract

1. Introduction

2. Results and Discussion

3. Materials and Methods

4. Conclusions

Author Contributions

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B-Site-Ordered and Disordered Structures in A-Site-Ordered Quadruple Perovskites RMn3Ni2Mn2O12 with R = Nd, Sm, Gd, and Dy

Abstract

1. Introduction

2. Results and Discussion

3. Materials and Methods

4. Conclusions

Author Contributions

Funding

Institutional Review Board Statement

Informed Consent Statement

Data Availability Statement

Acknowledgments

Conflicts of Interest

References

Share and Cite

Article Metrics

Article Access Statistics

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B-Site-Ordered and Disordered Structures in A-Site-Ordered Quadruple Perovskites RMn₃Ni₂Mn₂O₁₂ with R = Nd, Sm, Gd, and Dy