Growth and characterization of high temperature La₃Nb_0.5Ga_5.3Al_0.2O₁₄ (LNGA) and La₃Ta_0.5Ga_5.3Al_0.2O₁₄ (LTGA) piezoelectric single crystals

La₃Nb_0.5Ga_5.3Al_0.2O₁₄ (LNGA) and La₃Ta_0.5Ga_5.3Al_0.2O₁₄ (LTGA) single crystals were grown using the Czochralski method. Piezoelectric properties of LNGA and LTGA single crystals were measured and compared to La₃Ga₅SiO₁₄ (LGS) crystals, where the piezoelectric coefficient d₁₁ and electromechanical coupling factor k₁₂ were found to be on the order of 6-7 pC/N and ∼16%, respectively. The resistivity of LNGA was found to be 1.1 × 10⁸ Ω cm at 500 ^{{ring operator}}C, much higher than those values of LTGA and LGS (∼ 2.2 × 10⁷ Ω cm for LTGA and ∼ 9 × 10⁶ Ω cm for LGS). The RC time constant of LNGA crystal was found to be 224 μs at 500 ^{{ring operator}}C, while the values were 49 μs and 18 μs at the same temperature for LTGA and LGS, respectively. The good piezoelectric property, together with its high resistivity, exhibit LNGA single crystals a good candidate for piezoelectric applications at elevated temperature.