In Situ XPS and Impedance Spectroscopy Studies of (1 − X)ba0.5bi0.5feo3 − Xgd2o3 Ceramics with Negative Temperature Coefficient

Perovskite-phase (1 − x)Ba0.5Bi0.5FeO3 − xGd2O3 ceramics with negative temperature coefficient (NTC) were synthesized by solid-state reaction. X-ray diffraction (XRD) measurements showed that all samples exhibited a tetragonal perovskite structure. In addition, all samples showed a typical NTC effect; their room resistivity ρ25 and thermal constant B25/75 were regulated by the Gd2O3 doping content, and varied in the 4.70 × 105–4.72 × 106 Ω cm and 5573–6697 K ranges, respectively. In situ X-ray photoelectron spectroscopy (XPS) elucidated the conduction mechanism of Ba0.5Bi0.5FeO3-based ceramics was the electron hopping type, and the source of NTC effect was the change in the content of different valence ion pairs and the increase in electronic mobility with increasing temperature. Impedance analysis showed that the samples were electrically inhomogeneous, and their grain boundary resistance was higher than the grain resistance. The corresponding relaxation process might originate from the release of space charge and the ionization of oxygen vacancies.