Thermodynamics of Ammonium Halopallidates II. Heat Capacity and Thermodynamic Properties of (ND₄)₂PdCl₆ at Temperatures from 5 K to 325 K

Abstract

Abstract The heat capacity of deuterated ammonium hexachloropallidate (ND 4 ) 2 pDCl 6 was measured from 5 K to 325 K by adiabatic calorimetry. One λ‐shaped phase transition, absent in the protonated salt, was found in the curve for heat capacity against temperature. This transition reaches its maximum C p.m ≃ 150 · R at (30.2 ± 0.1) K with Δ trs S m 0 = (2.005 ± 0.009) · R ( R = 8.31451 J · K −1 · mol −1 ) and marks the change from the high temperature cubic structure to the low temperature tetragonal structure. The Debye temperature at 0 K equals (96.5 ± 2.4) K and below 10 K, only lattice vibrations make significant contributions to the heat capacity. Smoothed values of the standard thermodynamic quantities for pure (ND 4 ) 2 PdCl 6 are tabulated up to 320 K and the S m 0 (273.15 K) = (49.80 ± 0.05) · R .