Ferroelastic oxide materials

An interesting sub-group of ceramic materials is ferroelastic and exhibits a hysterysis in mechanical stress-strain behavior. The microscopic origin of the ferroelasticity is reorientation of ferroelastic domains under mechanical stress. Rhombohedral or o rthorhombic perovskite oxides are principally ferroelastic due to the crystal symmetry considerations. Ferroelastic behavior of these perovskites has also been established, but the mechanism for the domain formation/reorientation is not clear. In this pro ject the mechanism for domain reorientation will be elucidated by characterization of the non-elastic properties. Kinetics for the reorientation of domains will be studied by EBSP in-situ SEM studies under compression and tension as well as using in-situ neutron and X-ray diffraction. Domain reorientation under mechanical load represents a fundamental mechanism for obtaining the desired higher fracture toughness of ceramics, and the project will aim to enhance the fracture toughness of ferroelastic perovskites. The unit cell of ferroel astic materials is anisotropic, hence other properties will be influenced by the reorientation of the ferroelastic domains. Coupling between ferroelasticity and other functional properties will be studied to understand the coupling and to identify possibl e applications. Especially the effect of domain reorientation on optical (including acoustical) and electronic properties will be emphasized.