Polycrystalline oxide materials exhibit semiconductor properties due to grain boundary (GB) and grain characteristics, which enrich the variety of applications. However, how to regulate the energy band structure of grains and the potential barriers at GBs through defect engineering is crucial to achieve a high performance electronic device. Herein, it is found that Fe3+ ions can change the grain energy band structure of CaCu3Ti4O12 (CCTO) materials, which enhances the linearization of the resistance–temperature curve (ln ρ–1000/ T) in the high temperature region. First principles calculation indicates that Fe3+ doping narrows the forbidden band and induces new impurity energy levels in the forbidden band, which matches the conclusion that the resistivity–temperature dependence of grains shifts toward the low-temperature region as derived from impedance spectroscopy. This shift results in no monotonic variation in grain resistivity within the application temperature region, thus enhancing the linearity of the ln ρ–1000/ T curve of CCTO materials in the high temperature region. In addition, Fe3+ ions can modulate the activation energy of CCTO materials in a wide range by changing the activation energy of GBs, which broadens the temperature range of CCTO. The significance of this work lies not only in achieving linearization of CCTO materials for high temperature thermistor application, but more importantly, the method presented here provides an avenue for the study of polycrystalline semiconductor materials.
The cold sintering process (CSP) has been used for fabricating functional ceramics at a low sintering temperature. In this study, highly dense 0.3CaCeNbWO8‐0.7LaMnO3 composite ceramics have been successfully fabricated by CSP. The phase structure, microstructure, and electrical properties of composite ceramics have been investigated. The composite ceramic is mainly composed of a tetragonal CaCeNbWO8 phase with scheelite structure and an orthorhombic LaMnO3 phase with perovskite structure. The relative density of composite ceramic is 94.5%, and is higher than that of single phase ceramic. The resistivity of composite ceramic exhibits negative temperature coefficient characteristics, with an aging coefficient less than 2%. Such a sintering methodology is of great significance, since it provides a feasible idea for preparing composite ceramics.
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