Preparation And Electric Properties Of Barium Titanate Ceramics

Barium titanate ceramics, which have been developed in several decades years, are a kind of new functional ceramics. Today, they have been one of the most important functional ceramics and used as the basic raw materials in the composition of ceramic capacitors. The research of preparation and properties of barium titanate has been a focal point in the field of inorganic solid chemistry since the excellent dielectric properties of barium titanate were discovered in 1940s. However, the research of barium titanate was began only in recent years in our country and there is a lot of work to do.The preparation of barium titanate powders and ceramics has great effect on the grain size and density of barium titanate ceramics, which influences the electrical properties of barium titanate strongly. As a result of this, we chose the preparation and properties of barium titanate and doped barium titanate as the task. Barium titantae and doped barium titanate powders were synthesized by sol-gel process. Electric properties were studied by Electrochemical Impedance Spectroscopy (EIS). Information analysis of Impedance Spectroscopy of barium titanate ceramics was conducted with the help of the computer. The relationship between grain resistance, boundary resistance, dielectric constant, dielectric losses , and frequency was discussed in detail. In general, the main work is as the follows:1: Preparation and electric properties of barium titanatea Nanometer-sized barium titanate powders have been synthesized by sol-gel process from Ba(CH3COO)2 and titanium alkoxied and were characterized by SEM, XRD, IR and DTA.b: The electric properties of barium titanate ceramics were studied by EIS. The conclusion wras demonstrated that the dielectric constants and dielectric losses were both decreased as the frequency increased.2: Preparation and electric properties of rare-earth-doped barium titanate ceramicsa: La, Ce and Pr-doped barium titanate powders were synthesized by sol-gel process respectively. The degree of aliovalent substitution was0.01-0.05% and 0.1-0.5%. The results showed that the doping of rare-earth could decrease the grain size and increased the crystal lattice parameters.b: The electric properties of the rare-earth-doped barium titanate ceramics were measured by EIS. When the degree of aliovalent substitution was below a(different rare-earth had different degree), the barium titanate ceramics were still insulators, but the grain resistivity of barium titanate was decreased to some extent. When the degree of aliovalent substitution was between a and b, the barium titanate became semiconductors because of the electron compensation mechanism. When the degree of aliovalent substitution was above b, the barium titanate became insulators again because of the defect compensation mechanism.3: Preparation and electric properties of Bai-xPbxTiO3 ceramicsa: A series of solid solution Bai-xPbxTiC3 were synthesized by sol-gel process. The calcination temperature was reduced and the crystal lattice parameter was increased with the doping of Pb. And the transformation from cubic phase to tetragona phase became more easily.b: After measured by EIS, the results showed that the grain resistivity was reduced to some extent due to the volatility of Pb, which would affect the electric properties of Bai.xPbxTi03 ceramics greatly.