Structure, non-stoichiometry and thermodynamic properties of Bi1.85Sr2Co1.85O7.7−δ ceramics

• Cobaltite Bi1.85Sr2Co1.85O7.7−δ was prepared and its structure was refined.
• Oxygen non-stoichiometry of Bi1.85Sr2Co1.85O7.7−δ was determined by TG.
• Thermodynamic properties were measured by PPMS, DSC and drop calorimetry.
• The heat capacity was analyzed using combined Debye–Einstein model.

The structure and oxygen non-stoichiometry of misfit layered cobaltite Bi1.85Sr2Co1.85O7.7−δ was determined by Rietveld analysis and by thermogravimetric measurements. The heat capacity and enthalpy increments of pseudo-ternary oxide Bi1.85Sr2Co1.85O7.7−δ was measured by the relaxation time method (PPMS) from 2 K to 256 K, by differential scanning calorimetry (DSC) from 258 K to 355 K and by the drop calorimetry from 573 K to 1153 K. Above room temperature the temperature dependence of the molar heat capacity in the form Cpm = (305.8 + 0.07325 · T − 4702536 · T−2) J K−1 mol−1 was derived by the least-squares method from the experimental data. The heat capacity was analyzed in terms of a combined Debye–Einstein model. The molar entropy Sm∘(298.15)=317.7 J mol−1 K−1 was evaluated from the low temperature heat capacity measurements.