Lead‐free KNN and KTN Single Crystals: Piezoelectric and Electro‐Optic Properties

K 1− x Na x NbO 3 (abbreviated KNN) is a lead-free piezoelectric material that is considered one of the most promising replacements for lead-based piezoelectric materials due to its excellent piezoelectric, ferroelectric, and dielectric properties and high Curie temperature. This chapter studies the growth of pure KNN crystals, their electrical properties, the evolution of their piezoelectric properties, and their large strain. Meanwhile, electro-optic (EO) effect is an important method to control and modulate light signals by an applied electric field, widely used in optical communication, imaging, and storage. Potassium tantalate niobate (KTa 1− x Nb x O 3 , KTN) crystal has excellent EO properties: a large quadratic electro-optic coefficient; a fast response time of nanoseconds; a broad transmittance of 400–4000 nm; a high diffraction efficiency; and a large electrostrictive coefficient. It is of great significance and value to grow crystals with good EO properties, study the origin of large EO effect, and design EO devices in this chapter for improving the optical modulation efficiency and promoting the development of EO applications.