Phase relations, solubility and growth of potassium titanyl phosphate, KTP.

Potassium titanyl phosphate is an unusually good nonlinear optical material whose use is constrained because of the difficulty of growing crystals. Promising new hydrothermal conditions for growth have been discovered. The yield of the reaction: KH2PO4 + TiO2 -> KTiOPO4 + H2O is used to deduce the hydrothermal phase diagram KPO3 - TiO2 - H2O between 500C and 600C at 10 kpsi in the presence of the mineralizer, 1 m (molar) K2HPO4. It is shown that KTiOPO4, "KTP", is congruently saturating above 600 degrees and crystallizes as the sole solid in an excess of KPO3 below 600 degrees. Solubility is appreciable above 600 degrees. Phase equilibria and solubility results are used to find growth conditions (2 m KH2PO4, 70% fill, 375- 425C) with rates of KTP crystallization from a few mil/day to ~27 mil/day (~0.55 mm/day). Good quality crystal growth takes place at the lower rates. These results hold promise of practical growth at mild conditions where low carbon steel, comparatively inexpensive autoclaves can be used.