DIELECTRIC AND STRUCTURAL CHARACTERISTICS OF BA-BASED AND SR-BASED COMPLEX PEROVSKITES AS A FUNCTION OF TOLERANCE FACTOR

The temperature coefficient of the dielectric permittivity (tau(epsilon)) 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 tau(epsilon) 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 tau(epsilon) 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 tau(epsilon) at given values of t.