Evidence of a Glass-Liquid Transition in a Gold-Germanium-Silicon Alloy

摘要

Gold rich (73-81 at % Au) alloys of gold-germanium-silicon were 'splat'-cooled to an amorphous solid form. Thermal and rheological evidence of a glass-liquid transition in the Au sub 0.77 Ge sub 0.136 Si sub 0.094 alloys is reported. The transition was manifested thermally by an abrupt rise of 5.5 cal/gm. atom K in specific heat, C sub p, as the alloy was heated from 285 to 297K. Just above 297K C sub p starts to fall with increasing T on a reasonable extrapolation of the high-temperature C sub p-T relation of the liquid alloy. This thermal behavior could be repeated on the same sample after it had been carried through the transition and chilled again. The apparent glass transition temperature was increased by 1-3 degrees by increasing the heating rate by a factor of 16. The viscosity, Eta, of the amorphous alloy increases rapidly with falling temperature from 0.9 x 10 to the 9th power poise at 305 K to 1.4 x 10 to the 13th power poise at 285K and is described by the equation: Eta = 0.52 exp(1360/(T - 251.3)) poise. The steady isothermal viscosity is independent of stress over the range 3 to 140 Kg/sq cm. Our finding that abrupt temperature changes in the high viscosity regime shifts Eta rather little initially indicates that Eta depends primarily on configuration rather than temperature per se. Measurements of enthalpy and resistivity of the alloy in its various states are made. (Author)