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[MDR--Phase stability of solid solution La1-xRxRh3B (R = Gd, Lu and Sc) with cubic anti-perovskite type structure.pdf](https://mdr.nims.go.jp/filesets/afc62acf-e7b7-425b-aa57-89d0847f4796/download)

## Creator

Kunio Yubuta, Akiko Nomura, Kaoru Kouzu, [Takao Mori](https://orcid.org/0000-0003-2682-1846), Shigeru Okada, Toetsu Shishido

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[Phase stability of solid solution La1-RRh3B (R = Gd, Lu and Sc) compounds with cubic anti-perovskite type structure](https://mdr.nims.go.jp/datasets/4517e18f-95fd-49f6-bcaa-bebb6a1bf990)

## Fulltext

Crystal Structure of a Cu3Au-type compound CeRh3B01Phase stability of solid solutionLa1-xRxRh3B (R = Gd, Lu and Sc) compoundswith cubic anti-perovskite type structureKunio Yubutaa*, Akiko Nomurab, Kaoru Kouzuc, Takao Morid,e, Shigeru Okadac and Toetsu Shishidoba The Ultramicroscopy Research Center, Kyushu University, Kyushu University, Fukuoka 819-0395, Japanb Institute for Materials Research, Tohoku University, Sendai 980-8577, Japanc Department of Science and Engineering, Kokushikan University,Tokyo 154-8515, Japand Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japane Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba 305–8671, Japan*Corresponding author:The Ultramicroscopy Research Center, Kyushu University, Fukuoka 819-0395, JapanTel: +81-92-802-3488E-mail: yubuta.kunio.400@m.kyushu-u.ac.jpAbstractWe have investigated the solid solution range of single phase with a cubic anti-perovskite type structure, and behaviors of lattice parameters, hardness, and thermogravimetry–differential thermal analysis (TG-DTA) in the cubic anti-perovskite type La1-xRxRh3B (R = Gd, Lu and Sc) compounds. The cubic anti-perovskite phase exists over the entire composition range x from 0.0 to 1.0 for all La-Gd, La-Lu and La-Sc systems. Both the lattice parameters and the hardness in all La-Gd, La-Lu and This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed2La-Sc systems exhibit a linear dependence on the substitution x for La atom. The results of TG-DTA measurements indicate that the oxidation of the compounds in air starts at about 500-600 K. The mixed phases of RBO3, R2O3 and Rh are identified as oxidized products around x = 0.5. The oxidation onset temperature, and weight gains due to the oxidation depend on substitution x. The behavior of crystallographic and physical/chemical properties in the present compounds La1-xRxRh3B strongly depend on the atomic size of the rare-earth atoms forming the cubic framework.Keywords: cubic anti-perovskite type, solid solution range, X-ray diffraction, TEM, hardness, oxidation resistance.1. IntroductionMany studies of simple and complex perovskite-type oxides have been investigated because of the interesting features of superconductor, insulator-metallic transition, ion conduction characteristics, dielectric properties, ferroelasticity and so on [1]. Besides, noticeable studies on non-oxide cubic anti-perovskite and Cu3Au-type compounds [2-4] such as RRh3By and RRh3Cy, have been performed due to their high phase stability and hardness, which make them promising candidates for some applications at high temperature. R represents rare earth metals and boron (and carbon) site has non-stoichiometry with a range of 0.0 < y < 1.0. As shown Fig. 1, R, Rh and B atoms are positioned at This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed3vertices, the face-centered and body-centered sites of the cubic, respectively, in the RRh3B compounds [5]. In addition, theoretical investigations have been carried out by using the first-principle calculations to explain and predict structural, elastic and thermodynamic properties [6-8]. It was reported that the boron content variation in the boron-deficient RRh3By compounds induces changes of some properties. Solid solution ranges of boron content for RRh3By (R = La, Gd, Lu and Sc) compounds were determined by XRD analysis in Fig. 2(a) [9-13]. As listed in Table I, atomic radii are larger in order of La, Gd, Lu, and Sc. In La-system LaRh3By, the cubic anti-perovskite phase (space group: Pm―3m) exists only the boron content y equal 1.0. On the other hand, in Sc system ScRh3By, solid solution range of boron content y extends from 1.0 to 0.0. As indicated by a gray arrow, with increasing atomic size of rare earth atom, solid solution ranges become narrower. Fig. 2(b) shows a relationship between microhardness and lattice parameter for boron full-occupied RRh3B (R = La, Gd, Lu and Sc) compounds [9-13]. As we can easily see, the hardness linearly depends on a size of cubic anti-perovskite lattice. With decreasing the size of lattice (bond length), hardness becomes larger. A similar correlation appears for the boron-deficient RRh3By compounds. The correlation between bond length and hardness is consistent with reported results that some properties of RRh3By can be tuned by addition of boron located on the center of the rhodium octahedron. Subsequently, Zeiringer et al. carried out the Pd substitution for the Rh sites forming octahedrons [14]. It was investigated regarding the solid solution range for substitution of Rh and Pd atoms, the This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed4behavior of Ce valence and the lattice modulation for CeRh3-zPdzB0.5 (0 < z < 3) compounds. Although lattice expansion was confirmed, the behavior was not linear with Pd content. Increasing of the lattice size was monotonous at less than z = 1.5. The rate of increase was enhanced in the range of 1.5 < z < 2.4, and whereas it saturated at larger than z = 2.4. Valency and cell volume are intimately related parameters through the Coulomb potential acting on the valence electrons of the atoms. With increasing of Pd content z, the lattice parameter increases, whereas valence of Ce deceases from 4+ to 3+ though the intermediated state.In the present study, our interest is moved to the framework of cubic lattice formed by rare earth atoms (as indicated by a large arrow in Fig. 1). That is, there was an interest in the possibility of controlling physics and chemical properties by modulation of cubic framework in boron full-occupied LaRh3B compound by substituting other rare-earth atoms with different size, Gd, Lu and Sc, for La atoms. The scattering power of R atoms is sufficiently large that the structural singularity with the long-range and/or short-range order, if present, can be expected to be detected by X-ray and electron beam. We present results; (i) where the solid solution La1-xRxRh3B (R = Gd, Lu and Sc) could be obtained, when rare-earth atoms of different atomic sizes were used together, (ii) the effect of substitution on the hardness and (iii) the changing of the oxidation resistance with substitution.2. ExperimentalThis preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed5Polycrystalline samples of boron full-occupied La1-xRxRh3B (R = Gd, Lu and Sc) compounds were synthesized by the arc melting method using 99.9% pure La, Gd, Lu, Sc, Rh and B as raw materials. The button-like product was then turned over and re-melted three times to improve its chemical homogeneity. The synthesized samples were wrapped with Ta foils and annealed at 1573 K for 20 hrs in vacuo. It was confirmed that chemical compositions before and after synthesis are almost the same. In addition, contaminations from an electrode (tungsten) and a hearth (copper) cannot be detected. Lattice parameters of the polycrystalline samples were determined by powder X-ray diffraction (XRD). The micro-Vickers hardness (Hv) for the samples was measured at room temperature. A load of 300 g was applied for 15 s and 10 impressions were recorded for each sample. The obtained values were averaged. In order to investigate the oxidation resistance, thermo-gravimetric (TG) analysis and differential thermal analysis (DTA) were performed between room temperature and 1473 K to study the oxidation resistance of the samples in air. A sample of about 25 mg was heated at a rate of 10 K/min up to 1473 K. The final oxidation products were analyzed by powder XRD. A grain size of the presented sample is 20–30 m based on optical microscopy observation. Thin specimens for transmission electron microscopy were prepared by Ar ion milling. Selected area electron diffraction (SAED) patterns taken with the incident beams along three principal directions; [001], [011] and [111], were obtained from same regions using transmission electron microscope (TEM), JEOL JEM-This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed62000EXII, at accelerating voltage of 200 kV. High-resolution electron micrographs were taken with the incident beams along the [011] direction by using 200 kV TEM, TOPCON EM-002B.3. Results and DiscussionPowder XRD patterns of boron full-occupied La1-xScxRh3B compounds are shown in Fig. 3(a). From analysis of powder XRD patterns, it is confirmed that a single phase with cubic anti-perovskite structure (space group: Pm―3m) exists over the entire composition range x from 0.0 to 1.0 for the all systems. It was additionally confirmed that no splitting exhibits at diffraction peaks for all systems. In both La-Gd and La-Lu systems, the cubic anti-perovskite phase also exists without minor phases. Fig. 3(b) summarizes lattice parameters as a function of substitution for three systems. Triangles, squares and circles correspond to the La-Gd, La-Lu and La-Sc systems, respectively. With increasing substitution rare-earth atoms for La atom in all systems, lattice parameters linearly decrease. This tendency is coincident with the result of lattice parameter in Fig. 2(a). On the basis of these results, it can be concluded that the phase relation of cubic anti-perovskite type single-phase linearly depends on the substitution x. TEM observations were performed in order to clarify the local structure of boron full-occupied La1-xRxRh3B compounds. In our previous study, we reported that the observed SAED patterns of CeRh3B0.5 [15,16] and ScRh3B0.5 [17] compounds showed the appearance of 1/2 1/2 1/2–type This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed7superlattice reflections and fine satellite reflections around all Bragg reflections. The 1/2 1/2 1/2–type superstructure was characterized by the structural ordering of both the boron-vacancy and Rh atom in Rh octahedrons. The range of the appearance of 1/2 1/2 1/2-type superlattice reflections and fine satellite ones is consistent with that showing the abrupt drop of hardness, in boron content of 0.4 < x < 0.5 [10, 18]. In addition, SAED patterns of the Pd substituted CeRh3-zPdzB0.5 compounds revealed the appearance of 1⁄2 1⁄2 1⁄2–type superstructure and satellite spots with respect to the parent Cu3Au structure [14]. On the other hand, the 1⁄2 1⁄2 1⁄2–type superstructure is confined to the Rh-rich part of the solid solution CeRh3-zPdzB0.5, satellite reflections are observed throughout the solid solution. It was expected that La0.5Sc0.5Rh3B compound exhibits the most frustrated configuration among the present compounds, because of mixing the largest La and the smallest Sc atoms with a ratio of 1 : 1. Figures 4(a)-(c) show SAED patterns of the La0.5Sc0.5Rh3B compound, taken with the incident beams along the (a) [001], (b) [011] and (c) [111] directions. Even though there is a large difference of atomic size between La and Sc atoms in the present systems, however one can notice no signs of the structural singularity; i.e. superlattice spots, satellite spots and diffuse streaks. Figure 4(d) depicts a high-resolution electron micrograph taken with the incident beam parallel to the [011] direction. The image shows well-ordered and homogeneous bright dots without the displacive and occupancy modulations. These structural features suggest that no lattice modulations exist by the mixing of This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed8La0.5Sc0.5. That is, the ordering of the La and Sc atoms does not occur but both La and Sc atoms randomly locate at vertex sites. It is well known that the hardness is one of representative material parameters indicating the resistance to elastic/plastic deformation. This parameter reflects the nature of the chemical bonding. Figure 5 shows microhardness as a function of substitution x. With increasing substitution rare-earth atoms with small size for La atom, hardness linearly increases. Figure 6 shows a relationship obtained by combined microhardness and lattice parameter. From the result shown in Fig. 6, it can be recognized that there is a strong correlation between hardness and size of lattice (bond length) in boron full-occupied RRh3B compounds.In order to elucidate the nature of chemical bonds in the present compounds, TG-DTA measurements were carried out. Figure 7 shows (a) DTA and (b) TG curves of the La1-xLuxRh3B compounds as an example. Size of Lu atom is middle among Gd, Lu and Sc ones. The exothermic peaks at about 500-600 K correspond to oxidation for the present compounds. The oxidation products are listed in Table II. After the exothermic peaks of 500-600 K, LaBO, LuBO3 and Rh2O3 were produced around x equal 0.5. On the other hand, the endothermic peaks correspond to the decomposition at about 1300-1400 K. A common feature for all systems is that endothermic peaks appear at same temperature. As a result of thermal reduction, Rh2O3 was decomposed and elemental rhodium was obtained above 1300 K, as indicated by endothermic peaks. Oxidation onset temperature, This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed9and weight gains due to the oxidation depend on substitution x as shown Fig. 8. On the other hand, the maximum temperatures of endothermic peaks do not depend on the substitutions.4. ConclusionSingle-phase of cubic anti-perovskite structure can be obtained over the entire composition range x from 0.0 to 1.0 for La1-xRxRh3B (R = Gd, Lu and Sc) compounds based on the powder XRD measurements. Especially, in spite of combination with largest La and smallest Sc atoms, the largest size disparity amongst rare earth elements, the cubic lattice framework of the cubic anti-perovskite structure can be formed without any noticeable modulations. Electron diffraction indicates no structural modulation in the La0.5Sc0.5Rh3B compound. Both the lattice parameter and the hardness exhibit the linear dependence on the substitution x. By means of TG-DTA, the oxidation of the compounds in air starts at about 500-600 K. Around x = 0.5, the mixed phases of RBO3, R2O3 and Rh are identified as oxidized products. On the basis of results, it can be concluded that the behavior of crystallographic and physical/chemical properties in the present compounds strongly depend on the atomic size of the rare-earth atoms forming the cubic framework.AcknowledgementsKY was partly supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed10(Grants numbers JP19K05643, JP20H05258 and JP23K04373) and the GIMRT program (Proposal numbers 202211-RDKGE-0008, 202212-CRKKE-0020 and 202311-RDKGE-0001) at the Institute for Materials Research, Tohoku University, Japan. TM acknowledges support from JST Mirai Program JPMJMI19A1.This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed11References[1] M. A. Peña and J. L. G. Fierro, Chem. Rev. 101 (2001) 1981–2018.[2] H. Holleck, J. Less-Common Met. 52 (1977) 167–712.[3] P. Rogl, L. Delong, J. Less-Common Met. 91 (1983) 97–106.[4] S. K. Malik, S. K. Dhar, R. Vijayaraghavan, Bull. Mater. Sci. 6 (1984) 263–272.[5] H. Takei and T. Shishido, J. Less-Common Met. 97 (1984) 223–229.[6] R. Sahara, T. Shishido, A. Nomura, K. Kudou, S. Okada, V. Kumar, K. Nakajima, Y. Kawazoe, Comp. Mater. Sci. 36 (2006) 12–16.[7] F. Litimein, R. Khenata, A. Bouhemadou, Y. Al-Douri, S. Bin Omran, Molecular Phys. 110 (2012) 121–128.[8] A. Bouhemadou, G. Uğur, Ş. Uğur, F. Soyalp, R. Khenata, S. Bin-Omran, Comp. Mater. Sci. 54 (2012) 336–344.[9] T. Shishido, H. Yamauchi, K. Kudou, S. Okada, J. Ye, A. Yoshikawa, H. Horiuchi, T. Fukuda, Jpn. J. Appl. Phys. 36 (1997) L1436.[10] T. Shishido, J. Ye, S. Okada, K. Kudou, T. Sasaki, S. Isida, T. Naka, M. Oku, I. Higashi, H. Kishi, H. Horiuchi, T. Fukuda, J. Alloys Compd. 309 (2000) 107–112.[11] T. Shishido, J. Ye, K. Kudou, S. Okada, M. Oku, H. Horiuchi, T. Fukuda, J. Ceram. Soc. Jpn. 108 (2000) 683–686. [12] T. Shishido, K. Kudou, S. Okada, J. Ye, A. Yoshikawa, T. Sasaki, M. Oku, H. Horiuchi, I. Higashi, S. Kohiki, Y. Kawazoe, K. Nakajima, Jpn. J. Appl. Phys. 40 (2001) 6037–6038.[13] T. Shishido, J. Ye, S. Okada, K. Kudou, K. Iizumi, M. Oku, Y. Ishizawa, R. Sahara, V. Kumar, A. Yoshikawa, M. Tanaka, H. Horiuchi, A. Nomura, T. Sugawara, K. Obara, T. Amano, S. Kohiki, Y. Kawazoe, K. Nakajima, J. Alloys Compd. 408-412 (2006) 379–383.[14] I. Zeiringer, J.G. Sereni, M.G. Berisso, K. Yubuta, P. Rogl, A. Grytsiv, E. Bauer, Mater. Res. This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed12Express 1 (2014) 016101.[15] K. Yubuta, A. Nomura, K. Nakajima, T. Shishido, J. Alloys Compd. 426 (2006) 308–311.[16] K. Yubuta, A. Nomura, T. Yamamura, T. Shishido, J. Alloys Compd. 451 (2008) 301–304.[17] K. Yubuta, A. Nomura, K. Nakajima, T. Shishido, J. Alloys Compd. 471 (2009) 341–346.[18] T. Shishido, M. Oku, S. Okada, K. Kudou, K. Iizumi, S. Sawada, Y. Yoshizawa, A. Nomura, T. Sugawara, K. Obara, R. Sahara, K. Yubuta, H. Kojima, V. Kumar, M. Tanaka, K. Shimamura, S. Oishi, S. Koshiki, Y. Kawazoe, K. Nakajima, J. Alloys Compd. 426 (2006) 304–307.This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed13Table I. Atomic size of rare-earth atoms R atomic size of R/ nmLa 0.188Gd 0.180Lu 0.173Sc 0.161Table II. Oxidation products heated up to 1473 K in air after the oxidation process for La1-xLuxRh3B compoundsx oxidation products0.0 LaBO3 + Rh0.2 LaBO3 + Lu2O3 + Rh0.4 LaBO3 + LuBO3 + Rh0.6 LaBO3 + LuBO3 + Rh0.8 LuBO3 + Rh1.0 LuBO3 + RhThis preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed14Fig. 1 Crystal structure of cubic anti-perovskite type RRh3B. K. Yubuta et al.This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed15Fig. 2 (a) Solid solution ranges of boron content with lattice parameters for boron-deficient RRh3By (R = La, Gd, Lu and Sc) compounds. (b) Relationship between microhardness and lattice parameter for boron full-occupied RRh3B (R = La, Gd, Lu and Sc) compounds. K. Yubuta et al.This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed16Fig. 3 (a) XRD patterns of La1-xScxRh3B compounds. (b) Lattice parameters as a function of substitution for three systems. Triangles, squares and circles correspond to the La-Gd, La-Lu and La-Sc systems, respectively.K. Yubuta et al.This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed17Fig. 4 Electron diffraction patterns of the La0.5Sc0.5Rh3B compound, taken with incident beams parallel to (a) [001], (b) [011] and (c) [111] directions. Reflections are indexed with the cubic anti-perovskite type structure. (d) High-resolution electron micrograph taken with the incident beam parallel to the [011] direction.K. Yubuta et alThis preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed18Fig. 5 Microhardness as a function of substitution x. Triangles, squares and circles correspond to the La-Gd, La-Lu and La-Sc systems, respectively.K. Yubuta et al.This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed19Fig. 6 Relationship between microhardness and lattice parameter. Triangles, squares and circles correspond to the La-Gd, La-Lu and La-Sc systems, respectively.K. Yubuta et al.This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed20Fig. 7 (a) DTA and (b) TG curves of the La1-xLuxRh3B compounds.K. Yubuta et al.This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed21Fig. 8 Oxidation onset temperature and weight gains as a function of substitution x for the La1-xLuxRh3B compounds.K. Yubuta et al.This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed22Graphical abstractHighlights► The cubic anti-perovskite phase exists over the entire composition range x from 0.0 to 1.0 for La1-xRxRh3B (R = Gd, Lu and Sc) compounds. Both lattice parameter and the hardness exhibit a linear dependence on the substitution x.► TG-DTA measurements indicate that the oxidation of the compounds in air starts at about 500-600 K. A mixed phase of RBO3, R2O3 and Rh is identified as oxidized products around x = 0.5. This preprint research paper has not been peer reviewed. Electronic copy available at: https://ssrn.com/abstract=4912316Preprint not peer reviewed