X-ray studies of the thermal expansion and Debye temperatures of Pd-Ag-Au ternary alloys

Abstract

Using a Unicam high temperature powder camera 19 cm in diameter, the precision lattice parameters and the coefficients of thermal expansion of Pd-Ag-Au ternary alloys of the type Pd x -Ag (1−x) 2 -Au (1−x) 2 have been determined at different temperatures ranging from room temperature to 900 ° by the X-ray method. From the X-ray diffractograms, obtained on a Philips Diffractometer at room temperature, the Debye-Waller factors, Debye temperatures and the root-mean-square amplitudes of thermal vibration of these alloys have been evaluated. The composition dependence of the lattice parameter is examined. The lattice parameter increases with decreasing palladium concentration, but shows a negative deviation from Vegard's law as in the case of the binary systems Pd-Ag and Pd-Au. Both the thermal parameters, the thermal expansion coefficient and the r.m.s. amplitude of thermal vibration show a systematic variation with composition and no anomalous character is found as in the case of the hardness data for these alloys. A gradation is observed between the lattice parameter and the mean expansion coefficient on the one hand and between the lattice parameter and the Debye temperature on the other hand.