| Colossal permittivity(CP) materials have been widely investigated for the realization of modern electronic devices with high integration, high performance and miniaturization. The Ti1-x(In0.5Nb0.5)xO2(TINO) ceramic, a new type CP material which has been discovery recently, has not only colossal dielectric constant, but also low dielectric loss as well as good temperature and frequency stability. It exhibits immense potential for using in microelectronic devices and high energy storage devices. However, a series of scientific problems such as the relationship between structure and property, as well as the mechanism of colossal permittivity have yet to further study. Therefore, it is highly necessary to investigate the microstructure and dielectric properties of TINO ceramic systemically and explore its underlying related mechanism of the CP phenomenon.The dielectric properties of(Nb+In) and(Nb+Fe) co-doped Ti O2 ceramics were investigated thoroughly in this paper. The effect of doping level, annealing treatment on crystal structure, microstructure and properties was discussed systemically. The influence of different electrode interface on dielectric properties as well as I-V behavior had been explored through electrode effect in TINO ceramic. The possible origin of colossal dielectric permittivity in TINO ceramic has been explained by interfacial polarization as well as electron-pinned defect dipoles. Furthermore, this paper has also clarified the difference of dielectric properties between Ti1-x(Fe0.5Nb0.5)xO2(TFNO) and TINO ceramics, and the dielectric relaxation behavior of TFNO ceramic was also investigated.A series of TINO ceramics with different doping level were synthesized by conventional solid-state reaction method. Their microstructures and dielectric properties were measured systemically. It could be shown that the(Nb+In) dopants have a solubility larger than 15% in TINO ceramic with pure rutile phase. A colossal dielectric permittivity, reach to 105, could be achieved in TINO ceramics with dielectric loss below 0.2. Two types of dielectric relaxation processes, which contribute to the so-called “colossal dielectric permittivity”, can be easily distinguished in TINO with 5-15%(Nb+In) doping. Both sets of relaxation peaks shift to higher frequencies with increasing temperatures. The high frequency relaxation can be well fitted by Arrhenius equation with low level activation energy(55-113 me V), which indicating thermally activated carrier hopping, while the low frequency relaxation deviated from Arrhenius behavior but followed a VRH-like relationship, reflecting a variable range hopping process. Further analysis confirmed that the VRH-like relaxation mainly originated from a highly insulating barrier layer between electrodes and ceramics, and the high frequency relaxation was related to an electron-pinned defect dipole effect. It should be noted that TINO ceramics display obviously semiconducting features and then should not be used as a “colossal dielectric permittivity” material for industry.Rutile TFNO ceramics were fabricated successfully with In3+ replacing by Fe3+. Unexpectedly, TFNO ceramics showed quite different dielectric response to that of TINO. The CP behavior is virtually nonexistent in TFNO. Only one dielectric relaxation process was observed, which obeyed Arrhenius law with relative high activation energy. This dielectric relaxation was most probably attributed to the charge hopping between Fe2+ and Fe3+ ions. |
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