Study On Anti-reducing And Temperature Stability Of （Ca,Sr）TiO₃ Based Ceramics

With the increasing demands of low cost, base metal electrode multilayer ceramic capacitor（BME-MLCC） become the major trend gradually, which requires dielectric material to be co-sintered with base metal electrode in reducing atmosphere. Hence, the dielectric material sintered in reducing atmosphere with high permittivity and good temperature stability has been a research focus. The effects of doping and compositing on structure and dielectric properties of（Ca,Sr）TiO₃ based ceramics, which were applied in BME-MLCC dielectric materials, were studied in this article.The influences of CaF₂, MgO and LiF dopants on the structure and dielectric properties of Ca_0.36Sr_0.64TiO₃ ceramics were studied. XRD results indicated that all samples showed a cubic structure, and no second phase could be discovered. W hen the ceramic was doped with CaF₂ or LiF, the permittivity of samples sintered in reducing atmosphere did not show an obvious decline when compared with in air. When MgO was applied as dopants, the permittivity of samples sintered in reducing atmosphere had near ly doubled when compared with air, which is caused by the generation of oxygen vacancy. Moreover, the temperature coefficient of permittivity（） was below-900 /℃ for all samples. The results suggested that the samples sintered in reducing atmosp here can maintain high permittivity and low dielectric loss when doped with CaF₂, MgO or LiF, but there was no big improvement in temperature stability.The structure and dielectric properties of（1-x）Ca_0.36Sr_0.64TiO₃-xLi_0.5Pr_0.5TiO₃ composite（0.1≤x≤0.3） were studied. XRD result indicated the formation of solid solution and cubic perovskite structure for all samples. When samples were sintered in air, the permittivity declined from 274 to 254 with the increasing Li_0.5Pr_0.5TiO₃ content. Compared with samples sintered in air, the permittivity of samples sintered in reducing atmosphere rose by about 2³ times, whereas the dielectric loss rose by about 20³0 times. The dielectric peak shifted to higher temperature with the increasing Li_0.5Pr_0.5TiO₃ content, which caused that increased from-1238 /℃ to +55 /℃. The results suggested that the compositing of these two materials can effectively adjust the of samples. However, the samples showed a trend of semi-conducting, which meant a bad anti-reductive of materials.The structure and dielectric properties of（1- x）Ca_0.36Sr_0.64TiO₃-xLi_0.5Nd_0.5TiO₃ composite（0.3≤x≤0.8） were studied. XRD result indicated the formation of solid solution and cubic perovskite structure for all samples. When samples were sintered in air, the permittivity declined with the increase of Li_0.5Nd_0.5TiO₃ content, while the dielectric loss showed a contrary trend. The of air samples increased monotonically from-1556 /℃ to +2509 /℃ with the increase of x value. A near zero was achieved at x=0.57（=+12 /℃）. As for samples sinterd in reducing atmosphere, the dielectric peak shifted to higher temperature with the increasing Li_0.5Nd_0.5TiO₃ content, which caused that increased monotonically from-1389 /℃ to +2679 /℃. The impedance spectroscopy of（1-x）Ca_0.36Sr_0.64TiO₃-xLi_0.5Nd_0.5TiO₃ composite（0.3≤x≤0.8） sintered in reducing atmosphere were studied. The equivalent circuits of caramics were fitted based on “brick model”, and the parameters of different electroactive region were also calculated. The activation energy of samples was analyzed on basis of impedance spectroscopy data. A three factor and four level orthogonal exper iment was carried out to study the effect of Mn, V, Y dopants on Ca_0.36Sr_0.64TiO₃-Li_0.5Nd_0.5TiO₃ composite sintered in two kinds of atmosphere.