Crystal structure and thermal expansion of the third-order Ruddlesden-Popper phase Pr4Ni2.7Co0.3O10-δ (PNCO) were determined by high temperature X-ray powder diffraction (HT-XRD) and Rietveld analysis in the temperature range 25–600 °C in air. The thermal expansion coefficient (TEC) of PNCO is smaller compared with first-order Ruddlesden-Popper phases and in excellent agreement with values of common electrolytes of solid oxide cells. HT-XRD, thermogravimetry, and differential scanning calorimetry showed a reversible phase transition at 600–650 °C. A single monoclinic (P21/a) phase occurs at 25–600 °C, while a mixture of monoclinic and tetragonal (I4/mmm) phases is found at 650–900 °C. The oxygen nonstoichiometry was determined by thermogravimetry as a function of temperature (300 ≤ T/°C ≤ 900) and oxygen partial pressure (8.3 × 10−4 ≤ pO2/bar ≤ 8.3 × 10−1). Data of the oxygen nonstoichiometry were further evaluated with respect to the partial molar enthalpy and entropy of oxygen, and the thermodynamic factor of oxygen.
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