New axial Fe³⁺centres in stoichiometric lithium niobate crystals

Abstract

Two new axial Fe3+ centres. arising after reduction of stoichiometric lithium niobate crystals grown from melts containing K2O, were discovered and investigated by EPR. Their b20 crystal field parameters are equal to 495 and 688 (*10-4 cm-1) and are thus much smaller than b20 for the axial FeLi3+ centre, 1660*10-4 cm-1, which had been studied before. The models of Fe3+ centres in lithium niobate and lithium tantalate crystals are compared and the possible structures-FeNb3+ and FeNb3+-KLi-of the new centres are discussed.