Phase states and dielectric properties of sodium-potassium niobate solid solutions

The temperature dependence of dielectric constant ? for single crystals of Na_1?xK_xNbO₃ (0.04?x?0.15) is studied for the first time. From the shape of the ?(T) anomalies corresponding to rotational phase transitions, the type of interaction between the order parameters and the polarization is determined. A phenomenological model is developed which adequately describes the experimentally observed sequence of high-temperature (T>300°C) phase transitions, the dielectric anomalies associated with these transitions, and the changes in the phase states under the action of external factors (pressure, electric field).