ABSTRACT
This chapter is devoted to the next level of structure, namely, the arrangement of ions and atoms in crystalline ceramics. This topic is of vital importance because many properties, including thermal, electrical, dielectric, optical, and magnetic, can be quite sensitive to crystal structure. The chapter outlines some of the more important and obvious factors that determine the local atomic structure and how these factors can be used to predict the type of structure a certain compound can assume. Any crystal has to be electrically neutral, i.e., the sum of its positive charges must be balanced by an equal number of negative charges, a fact that is reflected in its chemical formula. Perovskites, like the spinels, are able to accommodate a large number of cationic combinations as long as the overall crystal is neutral. Ceramics are not always fully dense, however, and open porosities can create problems in measuring their densities.
