Growth And Dielectric Properties Of （InNb）_0.1Ti_0.9O₂ Single Crystal

Remarkable dielectric behavior was reported in（Nb+In） co-doped TiO2, which possessed colossal dielectric permittivity as well as low dielectric loss over wide temperature range, showing the possibility to replace the state-of-the-art CP materials. However, the mechanism that produces CP in such materials remains unclear, and the essential of two major mechanisms, electron-pinned defect-dipoles and internal barrier layer capacitor, were different. In the other hand, TiO2 as a very useful base material was widely applied in semiconductor, photo catalytic, dilute magnetic semiconductor and so on. But there was a very confused phenomenon in the progress of TiO2 single crystal growth: high growth rate could improve the crystal quality, which absolutely contrary to the theory of crystal growth. Researching the effect of growth condition to the TiO2 and（InNb）_0.1Ti_0.9O₂ crystal quality could help us to understand the single crystal growth progress of TiO2 base materials, and then could improve the crystal quality of TiO2 base materials.In this study, TiO2 and（InNb）_0.1Ti_0.9O₂ single crystals were grown by IR floating zone method. There must be some different of conditions for different furnace, so at first, we tried to find the best crystal growth conditions for TiO2 and research the influences of growth conditions to the crystal quality.TiO2 single crystals were grown by different rate（5¹4mm/h） in different atmospheres. Simples grown by high rate（14mm/h） have better quality then those grown by low rate（5mm/h）. This result appear to be similar to those observed by Koohpayeh. Through analysis, we found that decrease of thermal conduction at high temperature result in the crystal crack. At the same time, the crystal grown in O2 atmosphere was transparent yellow, but grown in air was transparent blue. This result mean that, the oxygen vacancy was very easily generated during grow progress for TiO2 and O2 could make up oxygen vacancy.In this study, a crack-free（InNb）_0.1Ti_0.9O₂ single crystal of 4 mm in diameter and 30 mm in length was successfully grown by the optical floating zone method. The polycrystalline feed and seed rods for growing the（InNb）_0.1Ti_0.9O₂ single crystal were prepared by solid-state reaction method. The oxygen partial pressure significantly affected the crystal quality of the material. As shown in reflecting polarizing microphotographs, crystals grown in air have fewer grain boundaries than those grown in pure oxygen; some air-grown crystals are completely free of grain boundaries. Compared to pure TiO2 crystal, the（Nb+In） co-doped TiO2 crystal required a lower growth rate of 5 mm/h to ensure high quality.After got high quality single crystal, we research the dielectric properties of different thickness simple by dielectric measurement and impedance spectroscopy. We found that the dielectric properties were very sensitive to the ratio of In3+/Nb5+. When the ratio close to stoichiometric, the dielectric permittivity was very low（¹000）. At last, we proved that the mechanism of colossal dielectric permittivity for（Nb+In） co-doped TiO2 ceramics was internal barrier layer capacitor.