FERROELASTICITY OF T-ZIRCONIA .1. HIGH-VOLTAGE ELECTRON-MICROSCOPY STUDIES OF THE MICROSTRUCTURE IN POLYDOMAIN TETRAGONAL ZIRCONIA

The microstructure of polydomain tetragonal zirconia (t'-ZrO2), i.e., a ZrO2 modification exhibiting ferroelastic behavior, is studied by hi gh-voltage electron microscopy. This material consists of three domain variants of the tetragonal phase with their c-axes nearly orthogonal to each other, Always two variants of these platelike domains are alte rnately arranged, forming elongated regular colonies, Hence, in both v ariants the common habit plane of the domains is a {110} twin plane. T he colonies are of columnar shape with a [111] longitudinal axis. They are bound by {110} planes, too, which are twin planes for the domains in the contiguous colonies. Owing to their particular structure and t he helical arrangement of the adjoining colonies, the material remains coherent and pseudocubic over large macroscopic regions, although it is formed by different tetragonal domains.