Temperature- and pressure-induced structural transitions in rare-earth-deficient R1-xNi2 (R = Y, Sm, Gd, Tb) Laves phases

E. Gratz, A. Kottar, A. Lindbaum, M. Mantler, M. Latroche, V. Paul-Boncour, M. Acet, Cl Barner, W. B. Holzapfel, V. Pacheco, K. Yvon

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48 Citations (Scopus)

Abstract

Electrical resistivity, thermal expansion, and temperature-dependent x-ray diffraction measurements on R1-xNi2 compounds give mutually consistent evidence for structural phase transitions at 740 K, 550 K, 600 K, and 450 K respectively for R = Y, Sm, Gd, Tb; 0 < x < 0.05. Arguments are given as to why most of the rare-earth-nickel compounds with the 1:2 ratio do not crystallize in the simple cubic Laves phase (C15 type) but show a superstructure of the cubic Laves phase at room temperature and at ambient pressure. This superstructure with the space group F43m and a doubled cell parameter is characterized by ordered vacancies on the R sites. It is shown that the observed structural instabilities result in transitions to the cubic Laves phase (space group Fd3m), however with disordered vacancies at high temperatures. High-pressure x-ray powder diffraction experiments show that the phase transition in Y0.95Ni2 shifts down to room temperature for a pressure of 27 GPa.

Original languageEnglish
Pages (from-to)8351-8361
Number of pages11
JournalJournal of Physics Condensed Matter
Volume8
Issue number43
DOIs
Publication statusPublished - 21 Oct 1996
Externally publishedYes

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