In search of inorganic nonlinear optical materials for second harmonic generation

In a search for inorganic oxide materials showing second-order nonlinear op tical (NLO) susceptibility, we investigated several berates, silicates, and a phosphate containing trans-connected MO6, octahedral chains or MO5 squar e pyramids, where, M = d(0): Ti(IV), Nb(V), or Ta(V), Our investigations id entified two new NLO structures: batisite, Na2Ba(TiO)(2)Si4O12, containing trans-connected TiO5 octahedral chains, and fresnoite, Ba2TiOSi2O7, contain ing square-pyramidal TiO5. Investigation of two other materials containing square-pyramidal TiO5 viz,, Cs2TiOP2O7 and Na4Ti2Si8O22. 4H(2)O, revealed t hat isolated TiO5, square pyramids alone do not cause a second harmonic gen eration (SHG) response; rather, the orientation of TiO5 units to produce -T i-O-Ti-O- chains with alternating long and short Ti-O distances in the fres noite structure is most likely the origin of a strong SHG response in fresn oite, (C) 1999 Academic Press.