Heat capacity and thermodynamic properties of deuterated ammonium hexafluorophosphate ND4PF6 from 5.8 K to 347 K

Abstract

The heat capacity of deuterated ammonium hexafluorophosphate ND4PF6 was measured from 5.8 K to 347 K by adiabatic calorimetry. Two [lambda]-shaped anomalies were found in the curve for heat capacity against temperature. The upper anomaly reached a peak Cp,m [approximate] 600[middle dot]R at (194.4 +/- 0.05) K with [Delta]trsSmo = (1.013 +/- 0.016)[middle dot]R (R = 8.3145J[middle dot]K-1[middle dot]mol-1). The lower anomaly is also [lambda]-shaped but is gradual, continuous, and reaches its maximum Cp,m = 19.2[middle dot]R at (137.5 +/- 1.0) K with [Delta]trsSmo = (0.562 +/- 0.011)[middle dot]R. Both anomalies are characteristic of order-disorder transitions. Smoothed values of the standard thermodynamic quantities are tabulated up to 350 K.