Crystal growth of K(Ta_1-xNb_x)O₃ solid solutions

Abstract

Single crystals of K(Ta_1-xNb_x)O₃ with compositions 0.30<x<1 are grown from solutions with an excess of K₂O. In order to minimize striations due to temperature fluctuations a method is applied similar to that known for the crystallization in aqueous solutions. With optimized growth conditions this kind of striations is fairly reduced. However, another type, so-called type II striations, is observed. They are formed by terraces at the growth interface. It is shown by electron microprobe measurements that the Nb/Ta ratio depends very strongly on the height of the terraces. In order to reduce type II striations Rb₂O is given to the solution and forced convection is applied. It is possible to restore the excess of K₂O completely by Rb₂O. As a result the crystals grown from these solutions are nearly striation-free. They are suitable for optical second harmonic generation (SHG) and holographic experiments.