New photo-refractive crystal useful for optical data storage

摘要

A process for producing a photo-refractive medium based on a perovskite crystal, especially a barium titanate crystal or a modified crystal, involves doping the crystal with preferably less than 1% of impurity atoms selected from V, Cr, Mn, Fe, Co, Ni, Mo, W, Ru, Rh, Pd, Re, Os, Ir, Pt, Cu, Ag, Au and rare earth elements. The novelty is that (a) the crystal is subjected to secondary doping with additional impurity atoms and to simultaneous or subsequent oxidation in an oxygen-containing atmosphere to ensure filling of oxygen vacancies, the secondary doping being carried out using impurity atoms of I, II or III main or subsidiary group elements, preferably Li, Na, K, Mg, Zn, Al, Ga, In and/or Sc; or (b) the crystal is subjected to secondary doping with Nb, La, Ta, Cl and/or F to reduce the primary dopant atoms or ions. Also claimed are similar processes in which (i) the primary dopant atoms are Ru, Rh, Pd, Re, Os, Ir, Pt, Ag or Au and are oxidised to a higher charge state by means of an oxygen-containing atmosphere; or (ii) the primary impurity atoms are Rh atoms or ions and are reduced to achieve x+ charge state by removing oxygen ions from the crystal lattice while simultaneously forming oxygen vacancies by means of an oxygen-deficient atmosphere so that Rhx+-V0 complexes are formed. Further claimed are novel crystals obtained by the above processes.