The impact of oxygen partial pressure during sintering on the electrocaloric effect of Ba0.7Sr0.3TiO3 ceramics

Barium strontium titanate (Ba0.7Sr0.3TiO3-BST) bulk ceramics were prepared using a conventional solid-state approach with different oxygen partial pressures in this work. The microstructures, oxygen vacancies, morphologies, permittivity and polarization were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, impedance analysis methods and polarization-electric field hysteresis measurements, respectively. The results indicated that the oxygen vacancies were introduced during the sintering in a reduced atmosphere, which leads to a significant impact on the electrocaloric effect (ECE) properties of BST ceramics. The ECE was measured directly using a thermocouple and modified differential scanning calorimetry. The optimal ECE temperature change of 2.18 K was obtained at 4 MV m−1 and 40 °C and a partial pressure of oxygen (PO2) of 6.14 × 10−7 atm, corresponding to an electrocaloric strength of 0.55 K MV−1 m−1.