Single crystal growth of langataite (La3Ta0.5Ga5.5O14) by vertical Bridgman (VB) method along [2 1¯ 1¯0] in air and in an Ar atmosphere

Piezoelectric langataite (La3Ta0.5Ga5.5O14: LTG) single crystals were grown along [2 1¯ 1¯ 0] (X-axis) by the vertical Bridgman (VB) method in air or in an Ar atmosphere. Using two kinds of raw materials, one with the stoichiometric composition of LTG and the other with a slightly Ga-rich composition, crack-free LTG single crystals 1 in in diameter were successfully grown both in air and in the Ar atmosphere. The colors of the crystal grown in air and in the Ar atmosphere were orange and pale green, respectively, and transparent in both cases. When the composition of the raw material used was stoichiometric, LaTaO4 was crystallized at the periphery of the crystal along (0 1 1¯ 0) but no other phase crystallization was observed at the end of the crystal. On the other hand, LaGaO3 was crystallized at the end of the crystal when the composition of the raw material was Ga-rich, while LaTaO4 was not observed at the periphery. We suggest that anisotropic segregation of Ta occurs in VB-LTG crystal growth for crystallization of LaTaO4 under a small temperature gradient in the radial direction.