Differences in vibrational entropy of disordered and ordered Cu3Au

Abstract
The difference between the heat capacities of chemically disordered and Ll2-ordered Cu3Au was measured by calorimetry from 70 to 300 K. By comparing these measured results with a harmonic heat capacity calculated with a Born-von Kámán model, we estimate the difference in vibrational entropy between disordered and ordered Cu3Au to be (0·14 ± 0·05)k B atom −1 at high temperatures. The smaller vibrational entropy of the ordered alloy originates from features of its optical modes, features which seem related to the different sizes of Cu and Au atoms.