Heat capacity, enthalpy and entropy of strontium niobates Sr2Nb10O27 and Sr5Nb4O15

Heat capacity and enthalpy increments of strontium niobates Sr2Nb10O27 (S2N5) and Sr5Nb4O15 (S5N2) were measured by the relaxation time method (2–275 K), DSC (253–353 K) and drop calorimetry (673–1371 K). Temperature dependencies of the molar heat capacity in the form Cpm = 835 + 0.23 T – 14 × 106/T2 J K−1 mol−1 for S2N5 and Cpm = 511 + 0.14 T – 6.6 × 106/T2 J K−1 mol−1 for S5N2 were derived by the least-squares method. The molar entropies at 298.15 K, Smo(S2N5, 298.15 K) = 759.7 J K−1 mol−1 and Smo(S5N2, 298.15 K) = 524.5 J K−1 mol−1, were evaluated from the low temperature heat capacity measurements.