Growth of large langatate (La₃Ta_0.5Ga_5.5O₁₄, LTG) crystals with high electrical resistivity

Large, 60 mm in diameter langatate (La₃Ta_0.5Ga_5.5O₁₄, LTG) crystals were grown with the Czochralski method in air. The full width at half maximum (FWHM) value of the rocking curve is 39.6″, and the piezoelectric coefficient d₁₁ value is 7.1 pC/N. The as-grown LTG crystal possesses excellent thermal properties, and the electrical resistivity at high temperatures (400∼600°C) was measured. After being heat-treated in Ar at 900, 1100, and 1300°C, the electrical resistivity increases evidently, and a La-rich and Ga-poor layer is observed on the surface of LTG. The LTG sample annealed in Ar at 1100°C for 10 h shows the highest electrical resistivity, which is up to 2.45*10⁸ Ω⋅cm at 500°C. The content of oxygen vacancies of LTG increased after the annealing procedure, and the defect model was used to explain the increase in high-temperature electrical resistivity. The obtained high-quality large LTG crystal can be used in the field of high-temperature piezoelectric sensors.