Improving interpretations of imperfections in insulating materials for current technologies

Abstract

Academic studies of imperfections in insulating crystals and glasses initially assumed the sites were simple and isolated. In part this was the result of the original simplistic characterisation and modelling. Unfortunately many textbooks, teaching and publications engrained this viewpoint. More detailed techniques invariably showed those ideas to be incorrect, with numerous examples of extremely long range interactions, multi-sites packages, and even phase separations or nanoparticle inclusions. Despite these examples, current defect models still often focus on extremely localised sites. This seems particularly inappropriate, as in many modern applications the materials are heavily doped, and in a powder format. It therefore seems essential to include, or reintroduce, analysis techniques which can reveal both the long range effects, and the variations that exist as a function of powder size and method of production. Where such data exist, they reveal considerable complexity. This overview thus comments on past and future analysis techniques with the sensitivity to enhance detailed models. Site models require, and will benefit from, a wider acceptance of medium and long range interactions. Realistically, many sites exist simultaneously, so models will never be perfect, but improved characterisation can assist not only the science, but also commercial developments. Inevitably there are self citations as we have actively exploited a range of techniques that can reveal evidence of long range defect production and sensitivity to extended lattice perturbations.