PHASE-DIAGRAM OF THE HOLMIUM SILICON BINARY-SYSTEM AND PHYSICAL-PROPERTIES OF HOLMIUM SILICIDES UP TO 1050 DEGREES-C

We have investigated the phase equilibria in the Ho-Si system over the entire range of alloy compositions. The phase diagram has been establ ished by means of differential thermal, X-ray and metallographic analy ses. Seven intermetallic compounds have been found to exist in the sys tem: Ho5Si3, Ho5Si4, HoSi1-x HoSi, Ho4Si5 and two Si-deficient compoun ds HoSi2-b and HoSi2-a. The paths of formation and the temperatures of phase transformations of all intermetallic compounds have been determ ined. The silicide Ho,Si, with the orthorhombic structure was discover ed by us for the first time. The silicides HoSi2-a and HoSi2-b are dim orphous. The solid solubility of holmium in silicon and that of silico n in holmium are both negligible (less than 1 at.%). The electrical re sistivity of both as-cast and heat-treated alloys was investigated at room temperature. Also, the temperature dependences of the electroresi stivity and thermal expansion of holmium silicides were studied at tem peratures up to 1050 degrees C.