Heat Capacity and Thermodynamic Functions of Neodymium Orthoniobate

The heat capacity of polycrystalline neodymium orthoniobate NdNbO4 in the range 2-1370 K is studied by relaxation, adiabatic, and differential scanning calorimetry. The existence of a magnetic transformation with a Neel temperature below 2 K in the low-temperature region is verified. The reversible phase transition at 987 K is shown to be a second-order transition. The contribution of the Schottky anomaly (Schottky contribution) to neodymium orthoniobate heat capacity is estimated. The gained data are used to calculate temperature-dependent standard thermodynamic functions in the range from 0 to 1400 K. Their values at 298.15 K are C-p degrees(298.15 K) = 121.4 +/- 0.4 J/(K mol), S degrees(298.15 K) = 134.7 +/- 0.5 J/(K mol), H degrees(298.15 K) - H degrees(0 K) = 21.24 +/- 0.17 kJ/mol, R EF degrees(298.15 K) = 63.43 +/- 0.21 J/(K mol).