CPC C30B 29/30 (2013.01) [C30B 15/00 (2013.01)] | 9 Claims |
1. A method for producing a lithium tantalate single crystal substrate having a volume resistivity of 1×1010 Ω·cm or more and less than 1×1012 Ω·cm, comprising:
heat-treating a lithium tantalate single crystal substrate having a volume resistivity of 1×1012 Ω·cm or more and having a single-domain structure, under normal pressure and at a temperature of 350° C. or higher but not higher than the Curie temperature thereof while burying it in a lithium carbonate powder having a BET specific surface area of 0.13 m2/g or more, wherein:
the lithium carbonate powder is a used lithium carbonate powder that has been used in burying a lithium tantalate single crystal substrate in heat treatment for the lithium tantalate single crystal structure under normal pressure and at a temperature of 350° C. or higher but not higher than the Curie temperature thereof,
in the heat treatment step, the heat treatment is carried out in a mixed gas atmosphere of an inert gas and a reducing gas at the start of the heat treatment, and after the heat treatment in the mixed gas atmosphere, the heat treatment is carried out in a single gas atmosphere of an inert gas, and
in an adsorption isotherm obtained in measurement of the BET specific surface area of the lithium carbonate powder, in which the horizontal axis is a relative pressure (adsorption equilibrium pressure (P)/saturation vapor pressure (P0)) and the vertical axis is an adsorbed amount (cm3/g), the inclination of the adsorption isotherm is 0.04 or more at a relative pressure (P/P0) falling within a range of 0.2 or more and 0.8 or less.
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