Abstract:
Perovskite-type single crystals, in particular lead-free potassium niobate crystals, attract a big attention due to considerable dependence of their piezoelectric properties and electromechanical response on the domain structure: A significant improvement of both properties was observed after poling such crystals along a specific direction. By applying external fields to a multidomain crystal one can control which of all possible domain states will appear in the crystal. In order to analyze average tensor properties of such a crystal we adopt a simple model in which multidomain crystals are represented by their domain configurations (DC), specified by partial volumes of individual states.

In order to provide assistance for further experimental studies we determine all macroscopic types of possible engineered domain structures in the Amm2-phase of potassium niobate crystals. It appears that in this case the number of types of the domain structures that can be, theoretically, produced by external fields is less than the number of possible types. For deriving tensor properties of domain structures the coherent DC's are of primary importance as they play role of appropriate basic units. We establish that, in addition to single domain states, electric field alone, or in combination with mechanical stress, may induce 6 non-equivalent coherent DC's. The results obtained by examining tensor properties of these DC's are presented. It is found that in 5 of 6 cases additional relationships between tensor components exist for certain material properties, compared to single domain crystals with same macroscopic symmetry.