Heat capacity, enthalpy and entropy of strontium bismuth niobate and strontium bismuth tantalate

The heat capacities and enthalpy increments of strontium bismuth niobate SrBi2Nb2O9 (SBN) and strontium bismuth tantalate SrBi2Ta2O9 (SBT) were measured by the relaxation method (2–150 K), Calvet-type heat-conduction calorimetry (305–570 K) and drop calorimetry (773–1373 K). The temperature dependences of non-transition heat capacities in the form Cpm = 324.47 + 0.06371T − 5.0755 × 106/T2 J K−1 mol−1 (298–1400 K) and Cpm = 320.22 + 0.06451T − 4.7001 × 106/T2 J K−1 mol−1 (298–1400 K) were derived for SBN and SBT, respectively, by the least-squares method from the experimental data. Furthermore, the standard molar entropies at 298.15 K Sm°(SBN)=327.15±0.80Sm°(SBN)=327.15±0.80 and Sm°(SBT)=339.23±0.72 J K−1 mol−1Sm°(SBT)=339.23±0.72 J K−1 mol−1 were evaluated from the low-temperature heat capacity measurements.