Unveiling the coupling effect of strain behavior and electro-optic property in nanodisordered KTN crystal

High-performance electro-optic (EO) crystals play a key role in optical communication and information processing. Potassium tantalate niobate (KTa1-xNbxO3, KTN) crystals advantageously have an ultrahigh quadratic electro-optic (QEO) coefficient and a wide transparency range, and their excellent QEO properties are closely related to polar nanoregion (PNR)-related polar units. Owing to the PNR-related polar units, KTN crystals have excellent strain properties, which makes them a potential multifunctional material. However, the relationship between strain behavior and QEO properties in nanodisordered KTN crystals has rarely been reported. The promotion of EO activity by regulating the PNRs-related polar units still needs to be studied. Here, we study the coupling effect of strain behavior and QEO properties in KTN crystals. The QEO, elastic-optic, electrostrictive, and elastic coefficients of KTN crystals are characterized, and the strain-QEO property coupling relation is established. The results show that the strain-induced QEO response significantly affects the QEO properties. The existence and response of PNRs near ferroelectric-paraelectric phase transition are demonstrated by variable-temperature x-ray diffraction and Raman spectroscopy. Combined with the heating and cooling QEO response time tests, the response of PNRs is shown to be an important reason for the enhancement of the QEO response of KTN crystals through the promotion of the strain-induced QEO response. This study provides guidance for clarifying the origin of the QEO properties of nanodisordered KTN crystals and is beneficial for further improving the EO properties of perovskite crystals by manipulating the strain behavior.