In-situ characterization of temperature-dependent domain structure and permittivity of KTN crystals with applied field

Abstract

Potassium tantalate niobate crystals exhibit excellent electro-optic properties in both tetragonal and cubic phases. However, domain walls typically induce light scattering, requiring high voltage poling to achieve transparency. This work investigated the effect of applied voltage during poling on the domain structure and permittivity of KTN crystals. As the applied external voltage increases, the dielectric permittivity first increases and then decreases. During this process, the domain walls of the crystal first become more densely packed and are subsequently eliminated by poling. The observed changes in the dielectric constant were explained using the modified Johnson model. By comparing the poling effects at different temperatures, it was obtained that the range of 3–5 °C below the Curie temperature is the optimal poling temperature range. By comparing the temperature-dependent permittivity under different voltages, it was found that the applied voltage can cause changes in the Curie temperature of the crystal. The relaxation factor of the KTN crystal under different voltages was obtained by fitting the temperature-dependent permittivity, showing that low electric fields can enhance the relaxation performance of ferroelectric materials. Finally, to verify the application effects of poled crystals, the evolution of domain structures under combined electrical and thermal influences was investigated. It was concluded that poled crystals near the Curie temperature are particularly sensitive to thermal effects, leading to the re-emergence of domain walls and reduced transparency. However, applying higher external voltages effectively prevents the formation of domain walls and minimizes light scattering.