| The High dielectric material is the important foundation of capacitors, memories, resonators, filters and other important electronic devices for developing a high performance and a size miniaturization Due to the miniaturization of devices and applications that require high energy density storage, the exploration of high dielectric materials is a hot research field of new materials at home and abroad in recent years. However, in a single material, achieving the synthetically dielectric properties including high dielectric, low loss, wide frequency band, good temperature stability and excellent resistance at the same time is still an extremely challenging task. In this context, this paper mainly did the research on the preparation, properties and related mechanisms of high dielectric ceramic materials (In, Nb) doping TiO2.TiO2 ceramics as the most original dielectric material that people did research on has a high relative dielectric constant, low dielectric loss, low conductivity and a very high electric field strength to combat wear. Therefore, the TiO2-based ceramic materials for the application of high energy density capacitor is a kind of dielectric material which has a very important value and meaning for research. Recently, the research group of the Australian National University reported that ceramics where (In, Nb) and other components co-doping into TiO2 has high dielectric properties. The research group achieved the permittivity ε’≥104, tanδ≤0.05 dielectric loss properties at the same time within the frequency of 1MHz below the experimentally measured frequency range, and exhibited the high dielectric constant and low dielectric loss less depending on temperature and frequency over a wide temperature range of 80K to 450K. We know that the dielectric constant of pure TiO2 is only 120 or so, while (In, Nb) doped TiO2 could increase the dielectric constant to 104, and the loss is kept below 0.05, which greatly improves the dielectric properties of TiO2. Although the physical mechanism that exhibit such a high dielectric constant of (In, Nb) doped ceramics still has some controversy, the finding of the outcome provides a new way for studying excellent dielectric properties of the material.This paper studied the preparation of (In, Nb) doped TiO2 ceramic samples by using the conventional solid-state reaction. It also studied the dielectric properties and how the sintering process and the milling time influence their dielectric properties of the different components of ceramics, and the initial exploration of the physical mechanism of the high dielectric properties of ceramics.1. Prepared a series of (In, Nb) doped TiO2 ceramic samples which have different sintering temperature by solid state reaction systematically examined their crystal structure, microstructure, dielectric spectrum and the spectrum of the complex impedance and electrical properties with the test temperature. Firstly, ceramic samples made by the use of ordinary sintering method have the regular change with the doping component, sintering temperature, holding time, and have a high dielectric constant. However, the samples prepared in this way have poor reproducibility, and the majority of the ceramic samples’ both low and high dielectric loss are more than 10%, while only the mid band has the lower loss. In order to ensure a high dielectric constant while reducing the loss of the sample, we prepared samples by using isostatic pressing, after the heat treatment of them, their dielectric properties has been greatly improved, especially in the dielectric properties of the sample annealed at 800℃. Dielectric constant at 10 mHz～10 MHz are stabilized at 104 or more, and the dielectric loss over a wide frequency range ef is less than 5%. Besides, its dielectric constant is essentially the same with the test temperature change, showing good temperature stability. In summary, the sample annealing after isostatic pressing sintering, has an excellent dielectric properties of various aspects.2. Studied some factors of why (In, Nb) doped TiO2 ceramics exhibit high dielectric constant, and preliminarily explored the physical mechanism of the origin of its high dielectric. By varying the ratio of the doping, that an excess of In and Nb would impact the dielectric properties of the ceramic has been found. Over doping In will reduce the dielectric constant and dielectric loss in ceramics, and the excess Nb will make ceramic dielectric constant and loss increase. The authors speculate that only proportional In and Nb-doped ceramic samples could appear the high dielectric constant and low loss. By surface treatment experiments, that the dielectric constant of samples after surface treatment sharply increased an order of magnitude has been found, and then after annealing, the dielectric constant of ceramic has returned to a lower value, which can speculate that the dielectric constant of the ceramic is related to the surface layer effects.3. The influence of different milling time on the dielectric properties of ceramics has been investigated. Through the analysis of powders’ SEM images before and after milling, it seems that prolonging milling time result in a more evenly dispersed powder, and XRD patterns also showed that there’s not many impurities of ZrO2. For the powders milling for 30h, after the dielectric spectrum test of samples sintered at different temperatures, it was found that the optimum sintering temperature is 1400℃. Additionally, after testing the dielectric spectrum and impedance spectra of the temperature changed sample, it showed that its dielectric properties at the range of test temperature is relatively stable, and this is also such a common rule of (In, Nb) doped TiO2 ceramic. |
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