Structure, oxygen non-stoichiometry and thermal properties of (Bi_0.4Sr_0.6)Sr₂CoO_5–δ

Highlights: • Cobaltite (Bi_0.4Sr_0.6)Sr₂CoO_5−δ was prepared and its structure was refined. • Oxygen non-stoichiometry of (Bi_0.4Sr_0.6)Sr₂CoO_5−δ was determined by TG. • Thermodynamic properties were measured by PPMS, DSC and drop calorimetry. • The heat capacity was analyzed using Debye–Einstein model and considering a variable oxygen stoichiometry. - Abstract: We synthesized and characterized (Bi_0.4Sr_0.6)Sr₂CoO_5−δ using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectroscopy (SEM–EDS). In the next step the heat capacity and enthalpy increments of (Bi_0.4Sr_0.6)Sr₂CoO_5−δ were measured by physical property measurement system (PPMS), differential scanning calorimetry (DSC) and drop calorimetry. Oxygen non-stoichiometry was determined using thermogravimetric measurement (TG) and reduction in hydrogen atmosphere. Above room temperature the temperature dependence of the molar heat capacity in the form C_pm = (201.0 + 0.09261 × T − 2184097 × T⁻²) J K⁻¹ mol⁻¹ was derived by the least squares method from the experimental data. The heat capacity was also analyzed in terms of a combined Debye–Einstein model. The molar entropy S_m^° (298.15) = 219.65 J mol⁻¹ K⁻¹ was evaluated from the low temperature heat capacity data