Oxygen non-stoichiometry and thermodynamic properties of Bi2Sr2CoO6+δ ceramics

In the literature the structure Bi2Sr2CoO6+δ has been described with a variable oxygen nonstoichiometry δ. We identified δ parameter by thermogravimetric measurements and determined thermodynamic properties of Bi2Sr2CoO6+δ. The heat capacity and enthalpy increments of Bi2Sr2CoO6+δ were measured by the relaxation time method (PPMS) from 2 to 256 K, by differential scanning calorimetry (DSC) from 258 to 355 K and by drop calorimetry from 573 to 1123 K. Above-room temperature, the dependence of molar heat capacity under isodynamical (constant pO2pO2) and conventional isoplethal conditions (constant composition) was derived from the experimental data by the least-squares method. The low temperature heat capacity was analyzed in terms of a combined Debye–Einstein model. The molar entropy Sm∘(298.15)=318.9 J K−1 mol−1 was evaluated from the low-temperature heat-capacity measurements.