Abstract: A substrate for surface acoustic wave element includes: a magnesium/lithium niobate single crystal in which an atomic ratio between Li and Nb satisfies 0.9048?(Li/Nb)?0.9685, and whose Mg content proportion is from 1% by mole or more to 9% by mole or less; or a magnesium/lithium tantalate single crystal in which an atomic ratio between Li and Ta satisfies 0.9048?(Li/Ta)?0.9685, and whose Mg content proportion is from 1% by mole or more to 9% by mole or less.

Abstract: The present invention provides a lithium tantalate (LT) single crystal or a lithium niobate (LN) single crystal, which has strong resistance to stress shock or thermal shock, and a surface acoustic wave filter comprising a piezoelectric substrate produced from the single crystal. The lithium tantalate single crystal or lithium niobate single crystal of the invention contains at least one additional element selected from the group consisting of iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, rhenium, scandium, rhodium, ruthenium, palladium, silver, platinum, gold, yttrium, neodymium, iridium, germanium, barium, cesium, strontium, gallium, cerium and other transition elements at a ratio of from 0.002 wt % or more to 0.1 wt % or less, and has excellent stress shock characteristics and thermal shock characteristics.

Abstract: To provide a wafer, made from a lithium tantalate single crystal or a lithium niobate single crystal, wafer which is charge restrained without impairing the piezoelectricity. Moreover, to provide a processing method and a processing apparatus therefor. It is characterized in that a wafer 50, made from a lithium tantalate single crystal or a lithium niobate single crystal, and a reducing agent 60, including an alkali metal or an alkali metal compound, are accommodated in a processing tank 2, and the inside of the processing tank 2 is held at a temperature of from 200° C. or more to less than a Curie temperature of the single crystal under decompression, thereby reducing the wafer 50.