Pressure dependence of the intra rare earth generalized binary phase diagram

Abstract

A generalized phase diagram for the trivalent intra lanthanide and yttrium-lanthanide binary alloys has been developed [1]. The single diagram represents a total of 91 binary phase diagrams. This paper extends this concept to take into account another variable — pressure. The generalized phase diagrams were established at 1, 2, and 4 GPa (10, 20 and 40 kbar). These diagrams clearly show that the b.c.c. phase as a function of pressure disappears in the light lanthanides, and is stabilized in the heavy lanthanides. This dependence can be understood in terms of the d occupation number, which increases with increasing pressure. The generalized phase diagram is also presented as a 25 °C isothermal section up to pressures of 24 GPa. The use of systematics enables one to calculate the phase relationships of the intra lanthanide alloys at various pressures between 0 and 4 GPa, and to evaluate the reliability of experimental results. Furthermore, an analysis of the pressure dependences of the various transformations indicates that 4f hybridization plays a significant (but probably not the major) role in determining the lanthanide crystal structures.