Systematics of the intra-rare-earth binary alloy systems

Abstract

A generalized phase diagram for the trivalent intra-lanthanide and yttrium-lanthanide binary alloys is proposed. This single diagram represents a total of 91 phase diagrams. A method of calculating unknown diagrams is described. These 91 diagrams can be classified into 13 types of phase diagrams, examples of 11 types are known, and a hypothetical diagram is calculated for the other two types. The lattice spacings of these intra-rare-earth alloys generally exhibit positive deviations from Vegard's law if the end-members have the same structure. This is consistent with the second-order elasticity model explaining deviations from Vegard's law. Both positive and negative deviations are found in the light lanthanide -heavy lanthanide alloys where the end-members always have different structures. These behaviors are explained on the basis of the d occupation number which decreases from the light lanthanides to the heavy lanthanides.