Effects Of LiBa₂（Ta,Nb）₅O₁₅ Additions On The Dielectric Properties Of BaTiO₃ Based Ceramics

With the rapid development of aerospace and oil exploration, there is a growing applications for multilayer ceramic capacitors fields under extreme conditions. In response to the environment protection and the strategy of sustainable development, it is necessary to prepare a dielectric materials with pollution-free, high dielectric constant, high temperature stability, low dielectric loss to meet the needs. Therefor, it is an urgent problem to solve to provide a high dielectric lead-free ceramic capacitor which have good temperature stability. Currently, doping is still the most effective way to optimize the performance of BaTiO3 ceramic, but few researches about the effects of tungsten bronze structured compound doping BaTiO3 to obtain high temperature stability were reported. In this study, BaTiO3 was the matrix and LiBa2(Ta, Nb)5O15 were added separately to modify its dielectric properties, then different contents of Na0.5Bi0.5TiO3 and Ca2+ were introduced to BaTiO3 to improve the temperature stability through depressing, shifting and boradening the dielectric peak.Firstly, (1-x)BT-xLBT ceramics were prepared by a conventional solid-state method and the effects of different LiBa2Ta5O15 contents on the temperature stability were investigated. The results showed that the dielectric peak was dramatically suppressed. (1-x)BT-xLBT solid solution could be formed within the limit of solubility of LiBa2Ta5O15 which played a role in grain refinement, and the samples exhibited the excellent dielectric properties. All the samples showed the diffuse phenomenon due to the substitution of Ta5+ for Ti4+ on the B-site caused compositional fluctuation. The dielectric constant at room temperature was enhanced to 2400～3000, and the temperature stability was obviously improved. The 0.996BT-0.004LBT ceramic exhibited the best temperature stability with TCC≤±15%, tanδ≤0.02 in the temperature rang of 22～125℃.Secondly, (1-x)BT-xLBN ceramics were prepared. The results showed that (1-x)BT-xLBN ceramics had higher dielectric constant and a better temperature stability when compared with LiBa2TasO15. In order to improve the temperature stability in high temperature range, different contents of Na0.5Bi0.5TiO3 were added to BaTiO3. The results showed that 0.92NBT-0.08BT-xLBN ceramics had low dielectric loss with tanδ≤0.02 in in the temperature range of 96～365℃. The 0.85BT-0.15NBT-xLBN ceramics were prepared. The results showed that the values of tetragonality and the average grain size were decreased. The chemical and structural disorder were caused by incorporation of LiBa2Nb5O15, then the classic ceramic gradually transformed into relaxor ceramics, and the pinched polarization loops could be observed. The 0.85BT-0.15NBT-0.004LBN ceramic exhibited excellent temperature stability with TCC≤±15% in the temperature range of 25～172℃. The dielectric constant at room temperature was 2500, the upper critical temperature was increased from 125℃ to 172℃.Thirdly, a certain amount of Ca2+ and more contents of Na0.5Bi0.5TiO3 were added to prepare 0.7BCT-0.3NBT-xLBNceramics. The results showed that the PNRS were formed due to the substitution of Nb5+ for Ti4+. According to superparaelectric mold, relaxor response could be obviously observed. The appearance of double peak resulted from the incorporation of LiBa2Nb5O15, then affected the distribution of ferroelectric field and non ferroelectric field. The positions of the two peaks changed in terms of the contents of LiBa2Nb5O15. The 0.996BT-0.004LBT ceramic showed good temperature stability with TCC≤ ±15% in the temperature range of 0～140℃. The dielectric constant in room temperature was 2528, the temperature stability was outstanding in the temperature range of 200～350℃.