Thermodynamic properties of the Ba0.75Sr0.25TiO3 nanopowders obtained by hydrothermal synthesis

Abstract

The paper is devoted to the investigation of the thermodynamic properties of nanostructured Ba0.75Sr0.25TiO3 perovskite material synthesized by hydrothermal method. The thermodynamic parameters obtained by a couple of measurements in both isothermal and dynamic regimes (drop calorimetry, solid-oxide electromotive force measurements, differential scanning calorimetry and thermogravimetry), allow for the investigations of the thermodynamic stability in a large temperature range from room temperature to 1273 K. The influence of the oxygen stoichiometry on the thermodynamic properties was examined using a coulometric titration technique coupled with electromotive force measurements. The results are discussed based on the strong correlation between the thermodynamic parameters and the charge compensation of the material system. X-ray powder diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) were used for the microstructure and morphology analyses. The variation of the thermal expansion and electrical conductivity associated with the structural changes has been evidenced by thermomechanical measurements and impedance spectroscopy, respectively. Through a combined analysis of all the results, new features related to the understanding of the strong interplay between the thermodynamic properties, microstructure, thermal expansion and electrical conductivity in the hydrothermally prepared Ba0.75Sr0.25TiO3 perovskite material have been revealed.