Patent ID: 7374612

Claim:
A method of producing a lithium-tantalate crystal, comprising: growing a lithium-tantalate crystal according to Czochralski method under an atmosphere which contains substantially no water vapor and has a dew point of minus 350° C. or lower to obtain a lithium-tantalate crystal wherein an optical absorption coefficient at a wave number of 3480 cm −1 is 0.3 cm −1 or less; subjecting the lithium-tantalate crystal to a single-polarization process; and subjecting the single-polarized lithium-tantalate crystal wherein an optical absorption coefficient at a wave number of 3480 cm −1 is 0.3 cm −1 or less to a heat treatment under a reducing atmosphere at a temperature of not lower than 250° C. and not higher than Curie temperature to obtain a single-polarized lithium-tantalate crystal wherein an optical absorption coefficient at a wave number of 3480 cm −1 is 0.3 cm −1 or less and an electric conductivity of 1×10 −12 Ω −1 ·cm −1 or more.