Interfacial morphology evolution of KTa1−xNbxO3 crystal growth

•Two-dimensional growth process of KTa1−xNbxO3 crystals was visualized.•Square-shaped crystal for {110} plane follows the two-dimensional nucleation mechanism.•Rod-shaped crystals for (001) plane are inclined to the rough interface growth mechanism.•Elements distribute more uniform in rod-shaped KTN crystals. Two-dimensional growth of Potassium tantalate niobate (KTa1−xNbxO3) crystals with x=0.94 was visualized by a high-temperature in situ observation system. Moreover, the interfacial morphology evolution and the interfacial kinetics during crystal growth were systematically studied by optical microscope. It was found that a square-shaped crystal surrounded by {110} planes was formed in the melt with small undercooling degree, while a large amount of rod-shaped crystals along with [001] direction predominated under large undercooling conditions. XRD results proved the orthorhombic phase of both shaped crystals. Interfacial kinetics analysis demonstrated the two-dimensional nucleation mechanism in the growth of square-shaped crystal. In contrast, the rod-shaped crystals were inclined to the rough surface growth mechanism. Furthermore, the surface compositional distribution of the as-grown crystal was carried out by EMPA, indicating that rod-shaped crystals had a smaller composition fluctuation than the square-shaped one, mainly due to the depressed segregating effect by the faster growth rate. The analysis of the mechanism and performance can promote the understanding of the KTN crystal.