Abstract
The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I–V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I–V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I–V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I–V behavior of (Nb + In) co-doped TiO2 ceramics.
Highlights
Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb 1 In) co-doped TiO2 ceramics
In order to verify the contribution of GBC effect to the colossal permittivity (CP) of (Nb 1 In) codoped TiO2, more solid evidences are still required besides the impedance spectroscopy
We provided two experimental approaches, by which the CP mechanism of (Nb 1 In) codoped TiO2 was explored
Summary
Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb 1 In) co-doped TiO2 ceramics. Synthesizing the co-doped TiO2 ceramics by CSSS and SPS techniques allows us to analyze the dielectric properties of co-doped TiO2 ceramics with different type of GBs. Secondly, the co-doped TiO2 ceramics sintered by CSSS technique were coated with micro-electrode by lithographic process, where the electrode is smaller than the grain, allowing us to analyze the I–V behaviors for single grain and GB. The co-doped TiO2 ceramics sintered by CSSS technique were coated with micro-electrode by lithographic process, where the electrode is smaller than the grain, allowing us to analyze the I–V behaviors for single grain and GB Based on these experiments, the properties of GB could be further explored and the role of GBC effect on the CP behavior of (Nb 1 In) co-doped TiO2 could be clarified
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