Hydrothermal growth of potassium tantalate niobate crystals

• The cubic KTa 0.63 Nb 0.37 O 3 crystals were successfully grown by hydrothermal method. • A KTN crystal with a size of 5.76 × 5.67 × 2.13 mm 3 was grown using cooling hydrothermal method at 700 °C and 150 MPa. • The growth rate of KTN crystals grown by temperature difference hydrothermal method can reach 0.12 mm/d. • KTN crystals grown by hydrothermal method have good thermal stability and good compositional uniformity. Potassium tantalum niobate (KTa 1−x Nb x O 3 , KTN) is a solid-solution crystal composed of potassium tantalate and potassium niobate, known for exhibiting the most substantial quadratic electro-optic effect recorded to date. The properties and crystallographic phases of KTN, varying from cubic (paraelectric) to tetragonal or orthorhombic (ferroelectric), are critically dependent on the tantalum-to-niobate ratio and the material’s homogeneity. KTN in the cubic phase, particularly near the cubic-tetragonal phase boundary, exhibits a high electro-optic coefficient, making it highly suitable for holographic storage applications. We employed both the cooling hydrothermal method and the temperature-difference hydrothermal method to obtain KTa 1−x Nb x O 3 (x = 0.37) crystals with uniform composition and high quality.