The role of chemical, polar and octahedral tilt disorder in high voltage/energy density ceramics

Abstract

Power modules in electric vehicles (EVs) are essential electronic components that manage and convert electrical power between the battery and other vehicle systems, such as the motor. The electronics are required to operate at higher temperatures (>200 oC) and fields (>0.5 MV/cm) than in conventional consumer goods such as phones and tablets. This requires the use of, e.g., SiC based semiconductor technology, along with associated filters/capacitors that can withstand high temperature/fields. Such capacitors have a large energy density arising from the ability of the dielectric to withstand repeated application of high fields (>0.5 MV/cm) without breakdown. This article reviews examples and presents new data and concepts on high energy density dielectrics intended for use in power electronic. In particular, the article focuses on a new class of dielectrics which have high permittivity (>1000) but do not saturate at high field and exhibit a quasi-linear polarisation-field response. The roles of chemical, polar and octahedral tilt disorder are assessed and a new mechanism proposed by which tilt disorder restricts strain coupling and therefore polar coupling, leading to a quasi-linear response in polarisation-field (P-E) loops. The influences of local variations in stoichiometry and multi-valent and multi-sized substituents in these polar lattices to attain enhanced resistivity are also discussed. The article therefore illustrates how a combination of high resistivity and tilt disorder are pivotal in the design of a new generation of high energy density capacitors for power electronics.