The growth and characterization of six inch lithium niobate crystals with high homogeneity

Abstract

As a kind of excellent piezoelectric material, lithium niobate (LiNbO₃) has been widely used for surface acoustic wave (SAW) devices. On a self-designed automatic diameter control system, large diameter (6 inch) LiNbO₃ crystals without cracks are successfully grown by choosing a suitable temperature gradient, starting composition, and growth parameters with the Czochralski method. The constituent phases of the LiNbO₃ crystals and their polycrystalline precursor are determined by X-ray powder diffraction, and the Li content along the crystal growth direction is determined by Raman scattering spectroscopy. The temperature gradient and growth parameters that influence the growth of the large diameter crystals are discussed in detail. The chemical analyses reveal that the 6 inch LiNbO₃ crystals have high homogeneity. The average Curie temperature is 1143.04 ± 1.3 °C, and the piezoelectric coefficient d₂₂ is up to 19.8 pC N⁻¹. The specific heat (C_p), thermal expansion coefficients (α_a and α_c), thermal diffusion coefficients (λ_a and λ_c), and thermal conductivities (κ_a and κ_c) of the LiNbO₃ crystals are also determined.