Top seeded solution growth of Rb-doped KNbO3 single crystals

We report the growth of Rb-doped potassium niobate (KRN) single crystals using the top seeded solution growth (TSSG) technique. Colorless and transparent KRN single crystals have been successfully grown from melt comprising up to 15 mol% of Rb. Atomic absorption measurements indicate that the Rb content in the KRN solid solution is rather low, the Rb segregation coefficient being on the order of 0.05. Based on crystal energy considerations, the most probable Rb location in the host lattice is expected to be the lattice site of the K+ cation. It is believed that the substitution of K+ by a much larger Rb+ has given rise to a lattice misfit in the doped bulk crystal, and thereby increased the total free energy of the crystal. From the thermodynamics point of view, the segregation phenomenon tends to reduce the lattice strain within the bulk crystals, hence, resulting in the segregation coefficient of Rb being rather small.