Hydrothermal growth of OH-free AlPO4 and GaPO4 crystals, the way of twin reducing

Water-free crystals of AlPO4 and GaPO4 have been grown in the temperature region 350-500°C by the direct temperature gradient technique under hydrothermal conditions. The concentrated solution of phosphoric acid with boiling temperature 225-240°C has been used as solvent. The characteristic features of twins in the crystals have been found and explained. The investigations of growth kinetics the specific features of twinning and growth mechanism have resulted in the choice of the seeds with special shape, size and orientation for growing crystals with lower quantity of twins and dislocations