NEW AXIAL FE3-NIOBATE CRYSTALS( CENTERS IN STOICHIOMETRIC LITHIUM)

Two new axial Fe3+ centres, arising after reduction of stoichiometric lithium niobate crystals grown from melts containing K2O, were discove red and investigated by EPR. Their b2(0) crystal field parameters are equal to 495 and 688 (x 10(-4) cm- 1) and are thus much smaller than b 2(0) for the axial Fe(Li)3+ centre, 1660 x 10(-4) cm-1, which had been studied before. The models Of Fe3+ centres in lithium niobate and lit hium tantalate crystals are compared and the possible structures-Fe(Nb )3+ and Fe(Nb)3+-K(Li)-of the new centres are discussed.