High temperature and high energy density dielectric materials

This paper summarizes some of the recent work that has been conducted in search of new dielectric ceramic materials that can operate at temperatures between 180 to 350°C. High temperature perovskite relaxor materials were developed with compositions close to morphotropic phase boundaries (MPB) within xBi(Me'Me'')O₃-yPb(Mg _1/3 Nb _2/3)O ₃-zPbTiO₃ ternary solid solutions. These materials show classical relaxor behavior with relative permivittivies ∼12,000, and T _max∼270 to 300°C. Binary solid solutions with (1-x) BaTiO₃-xBi(Me'Me'')O₃, e.g: 0.35 BaTiO₃-.0.65 BiScO₃ have a much suppressed relaxor characteristic with relative permittivities ∼1000, and these materials have relatively weak voltage saturation, and therefore can maintain relatively stable energy densities ∼8 J/cm³ in multilayer form up to relatively high temperatures ∼200°C. Other opportunities for dielectrics is in non-ferroelectric dielectrics, here commercial COG dielectric capacitors with a relative permittivity ∼35, that are cofired with nickel multilayer electrodes and based on 0.95CaZrO₃-0.05 SrTiO₃ binary solutions are contrasted against commercial polymer capacitors. It is found in the COG capacitors the energy density ∼ 5 J/cm³ and high temperature performance∼200°C with capacitors approaching 1microFarad. With recoverable energy density as a key parameter, the dielectric breakdown strength is very important, recently we have considered the use of an alkali free glass when the thickness is of the order 20 microns and below. Here the energy densities have been observed as high as 35 J/cm³, the other attractive characteristics noted is preliminary evidence of graceful failure processes in these dielectric glasses.