Abstract
The temperature coefficient of the dielectric permittivity (τε) of nonferroelectric complex perovskites is of importance in the application of these cermaics to microwave filters and resonators. Recent work has directly related changes in the τε of complex perovskites to the onset of structural phase transitions which involve tilting of the octahedra. It can be argued that the onset of octahedral tilting is controlled by the tolerance factor (t). Thus, a relationship between τε and t is postulated. This relationship is discussed and transmission electron microscopy is used to demonstrate examples of the structural modifications which cause the anomalies in τε at given values of t.