Growth of langasite via Bridgman technique along [0 0 0 1], [2 1̄ 1̄ 0] and [0 1 1̄ 1] for piezoelectric applications

2-inch langasite (La₃Ga₅SiO₁₄) single crystals were grown for the first time via a vertical Bridgman method, assisted by the accelerated crucible rotation technique (ACRT) along [0 0 0 1] (Z-axis), [2 1̄ 1̄ 0] (X-axis) and [0 1 1̄ 1] (54°-rotated Y-axis) for piezoelectric applications. Because of the possible liquid immiscibility, incongruency and segregation, secondary phases other than langasite are formed during growth. The mode of occurrence of these phases was closely related to the interface instability that was specific to the growth direction. The formation of inclusions consisting of lanthanum gallate (LaGaO₃), aligned parallel to (0 1 1̄ 0), was associated with the constitutional supercooling. The residual products during the terminal transient were the mixture of gallium oxide (Ga₂O₃) and lanthanum gallate (LaGaO₃) or the mixture of gallium oxide and lanthanum silicate (La₂Si₂O₇) reflecting the position of the initial melt, relative to the tie line connecting the langasite solid solution with gallium oxide in the system of La₂O₃-Ga ₂O₃-SiO₂. The homogeneity of the grown crystal was evaluated by the distribution of SAW velocities of the devices fabricated on the (0 1 1̄ 0) wafer, as well as by the uniformity of d-spacing of 0 5 5̄ 5.