► The heat capacity of Pt–Rh and Ag–Pd alloys was measured from 5 to 700 K. ► The Ag–Pd data were compared to those obtained by ab intio calculations. ► The extent of the excess entropy of 10 binaries was described by a simple relation.
The paper presents new calorimetric data on the excess heat capacity and vibrational entropy of mixing of Pt–Rh and Ag–Pd alloys. The results of the latter alloy are compared to those obtained by calculations using the density functional theory. The extent of the excess vibrational entropy of mixing of these binaries and of some already investigated binary mixtures is related to the differences of the end-member volumes and the end-member bulk moduli. These quantities are used to roughly represent the changes of the bond length and stiffness in the substituted and substituent polyhedra due to compositional changes, which are assumed to be the important factors for the non-ideal vibrational behaviour in solid solutions.