METHOD FOR THE REDUCTION OF IRON IN IRON-DOPED LITHIUM NIOBATE CRYSTALS

摘要

1433607 Iron doped lithium niobate crystals RCA CORPORATION 17 July 1973 [30 Oct 1972] 33977/73 Heading C1A A crystal useful for recording phase holograms comprises a single crystal of lithium niobate containing up to 0À1 mol. per cent of iron, wherein from half to almost all of the iron present is in the divalent state and wherein substantially all of the visible optical absorption is derived from divalent iron. A method used for reducing iron in an iron doped lithium niobate crystal, without substantially reducing the lithium niobate, comprises surrounding an iron doped lithium niobate crystal in a high melting salt of lithium and heating at a temperature of at least 400‹ C. in an oxygen containing atmosphere. It is preferred to heat the crystal in an atmosphere of oxygen at a temperature within the range 400-1000‹ C., the optimum temperature being dependent on the amount of iron present in the crystal. Lithium carbonate in powder form is the preferred lithium salt, but the silicate, oxide and fluoride can also be used, and the lithium salt surrounds the lithium niobate crystal while heated in a platinum crucible.