Heat capacity, enthalpy and entropy of SrBi2O4 and Sr2Bi2O5

Highlights: ► Heat capacity, enthalpy and entropy of ternary strontium bismuth oxides SrBi2O4 and Sr2Bi2O5. ► Heat capacity by DSC calorimetry and heat-pulsed calorimetry. ► Enthalpy increments by drop calorimetry. ► Einstein–Debye model for low-temperature dependence of the heat capacity. ► Entropy–volume correlation in the systems SrO–Bi2O3 and CaO–Bi2O3. - Abstract: Heat capacity and enthalpy increments of ternary strontium bismuth(III) oxides SrBi2O4 and Sr2Bi2O5 were measured by the relaxation time method (2–210 K), DSC (253–352 K) and drop calorimetry (570–1072 K). Temperature dependencies of the molar heat capacity in the form Cpm = 161.97 + 45.936 × 10−3T – 1.7862 × 106/T2 J K−1 mol−1 and Cpm = 197.48 + 87.463 × 10−3T – 1.9282 × 106/T2 J K−1 mol−1 for SrBi2O4 and Sr2Bi2O5, respectively, were derived by the least-squares method from the experimental data. The molar entropies at 298.15 K, S°m(298.15 K) = 206.1 ± 1.1 J K−1 mol−1 for SrBi2O4 and S°m(298.15 K) = 261.2 ± 1.4 J K−1 mol−1 for Sr2Bi2O5, were evaluated from the low temperature heat capacity measurements.