Potassium-tantalate-niobate mixed crystal thin films for applications in nonlinear integrated optics

Perovskite potassium tantalate-niobate mixed crystals (KTa 1−x Nb x O 3 with 0 ≤ x ≤1, KTN) undergo a phase transition from a paraelectric cubic to a ferroelectric tetragonal structure with decreasing temperature [1]. By adjusting the Ta/Nb content one can tune the phase-transition temperature of KTN and thus also its main properties at a given temperature. For example, the phase transition occurs around room temperature for x = 0.4, accompanied by changes in the dielectric and electro-optic (EO) properties [2]. This extremely promising material is of great interest because of its large EO effect and excellent nonlinear optical performance [2, 3]. However, due to the fact that the crystals grown have compositions being different from those of the molten ingredients, high-quality and homogeneous single-crystalline KTN is difficult to produce, which is limiting the application of this material [4, 5].