Phase relationships and low temperature heat capacities of alloys in the Y_5Si_4-Y_5Ge_4 pseudo binary system

摘要

Phase compositions and crystal structures of 10 Y_5Si_xGe_(4-x) alloys with x varying from 0 to 4 have been studied by means of X-ray powder diffraction, and their heat capacities at constant pressure have been measured from approx 4 to 350 K using semi-adiabatic calorimetry. The silicide, Y_5Si_4, belongs to the Gd_5Si/_2Ge_2-type crystal structure; the germanide, Y_5Ge_4, belongs to the Sm_5Ge_4-type crystal structure. Two solid solutions exist in the Y_5Si_xGe_(4-x) system: alloys with x varying from 4 to 3.5 have the monoclinic Gd_5Si_2Ge_2-type structure, and alloys with x varying from 3.0 to 0 have the orthorhombic Sm_5Ge_4-type crystal structure. Low temperature heat capacity data indicate the absence of structural transitions below room temperature. The existence and terminations of the solid solution regions of the four structures which occur in the R_5Si_xGe_(4-x) systems, where R is a rare earth element, correlate with the radius ratio of the R metal divided by the weight average radius of the Si and Ge atoms in the given phase.