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A. Lindbaum, E. Gratz, S. Heathman:
"Pressure-induced order-disorder transitions in RNi₂ compounds";
Physical Review B, Vol. 65 (2002), S. 134114-1 - 134114-6.

Most of the RNi2 compounds (R5rare-earth element! do not crystallize in the cubic Laves phase structure (C15), but in a superstructure of C15 with ordered vacancies at the R sites. In the present work high pressure x-ray diffraction experiments on selected RNi2 compounds (R5Tb,Sm,Gd, and Y) are presented, showing that pressures of about 8?15 GPa lead to a disordering of the vacancies in all of them. Furthermore the studies show that the pressure-induced order-disorder transition is closely related to the earlier observed disordering of the vacancies at high temperatures between 430 (TbNi2) and 740 K (YNi2), and that there is a pronounced variation of the transition pressures and temperatures among the investigated compounds. The driving mechanism behind these transitions is discussed.