Synthesis, boron-nonstoichiometry and hardness of perovskite-type rare earth rhodium borides RRh3Bx (R = La, Gd, Lu and Sc)

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

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Abstract

Rare earth ternary borides, RRh3Bx (R = La, Gd, Lu and Sc) have been synthesized by arc melting method. Borides RRh 3Bx (R = La, Gd, Lu and Sc) have perovskite-type cubic structure: space group Pm3m; Z = 1. The lattice parameters a of the stoichiometric RRh3B for R = La, Gd, Lu and Sc are 0.4251(1), 0.4183(1), 0.4126(1) and 0.4080(1) nm, respectively. LaRh3B x does not have boron-nonstoichiometry as x = 0. In GdRh 3Bx and LuRh3Bx, boron- nonstoichiometry ranges between 0.55 ≦ x ≦ 1 and 0.30 ≦ x ≦ 1, respectively. The boron-nonstoichiometry range is the widest, 0 ≦ x ≦ 1, for R = Sc. Boron-nonstoichiometry increases with decreasing atomic radius of R. The microhardness of the stoichiometric RRh3B for R = La, Gd, Lu and Sc is 4.2 ± 0.1, 6.8 ± 0.1, 7.7 ± 0.5 and 9.9 ± 0.1 GPa, respectively. As a result, microhardness increases with decreasing atomic size of R in RRh3B; R is positioned at the eight corners of the cube in the perovskite-type structure. Thus, hardness is strongly dependent on R element. The hardness changes almost linearly with boron concentration x for R = Gd and Lu in RRh3Bx, while no linear dependency is found for R = Sc. Ab initio calculations have been performed to obtain the equilibrium lattice constants and the bulk moduli. The calculated lattice constants are in excellent agreement with experimental results.

Original languageEnglish
Pages (from-to)379-383
Number of pages5
JournalJournal of Alloys and Compounds
Volume408-412
DOIs
Publication statusPublished - 2006 Feb 9
EventProceedings of the Rare Earths'04 in Nara, Japan -
Duration: 2004 Nov 72004 Nov 12

Keywords

  • Boron-nonstoichiometry
  • Microhardness
  • Perovskite-type phase
  • RRhB (R = La, Gd, Lu and Sc)

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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    Shishido, T., Ye, J., Okada, S., Kudou, K., Iizumi, K., Oku, M., Ishizawa, Y., Sahara, R., Kumar, V., Yoshikawa, A., Tanaka, M., Horiuchi, H., Nomura, A., Sugawara, T., Obara, K., Amano, T., Kohiki, S., Kawazoe, Y., & Nakajima, K. (2006). Synthesis, boron-nonstoichiometry and hardness of perovskite-type rare earth rhodium borides RRh3Bx (R = La, Gd, Lu and Sc). Journal of Alloys and Compounds, 408-412, 379-383. https://doi.org/10.1016/j.jallcom.2005.04.113