Thermodynamic properties of tubular cobaltite Bi3.7Sr11.4Co8O29−δ

• Tubular cobaltite Bi3.7Sr11.4Co8O29−δ was prepared and its structure was refined.
• Oxygen non-stoichiometry of Bi3.7Sr11.4Co8O29−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.

We synthetized a tubular cobaltite Bi3.7Sr11.4Co8O29−δ ceramics and characterized it using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The simultaneous thermal analysis (STA) revealed a very unusual thermal behavior which was eventually ascribed to metastability of tubular phase at lower temperatures. The heat capacity and enthalpy increments were measured by physical property measurement system (PPMS), differential scanning calorimetry (DSC) and drop calorimetry. The 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 was derived by simultaneous least squares method from DSC and enthalpy data. The heat capacity was also analyzed in terms of a combined Debye–Einstein model. The molar entropy Smo (298.15) = 1349.45 J mol−1 K−1 was evaluated from the low temperature heat capacity data.