HEAT-CAPACITY AND THERMODYNAMIC PROPERTIES OF DEUTERATED AMMONIUM HEXAFLUOROPHOSPHATE ND4PF6 FROM 5.8-K TO 347-K

The heat capacity of deuterated ammonium hexafluorophosphate ND4PF6 was measured from 5.8 K to 347 K by adiabatic calorimetry. Two λ-shaped anomalies were found in the curve for heat capacity against temperature. The upper anomaly reached a peak Cp,m ≈ 600·R at (194.4 ± 0.05) K with ΔtrsSmo = (1.013 ± 0.016)·R (R = 8.3145J·K-1·mol-1). The lower anomaly is also λ-shaped but is gradual, continuous, and reaches its maximum Cp,m = 19.2·R at (137.5 ± 1.0) K with ΔtrsSmo = (0.562 ± 0.011)·R. Both anomalies are characteristic of order-disorder transitions. Smoothed values of the standard thermodynamic quantities are tabulated up to 350 K. © 1990.