Structural studies of KNbO3 in niobate glass-ceramics

Potassium niobophosphate glasses and glass-ceramics of the family [xNb(2)O( 5).(50 - x)P2O5. 50K(2)O]:yFe(2)O(3) were studied by X-ray powder diffracti on, Mossbauer, infrared and Raman scattering spectroscopy. For the potassiu m-phosphate samples [50P(2)O(5)-50K(2)O], the iron oxide presents a network forming behavior for 5 mol% of Fe2O3 doping. From our Mossbauer analysis, high spin Fe2+ and Fe3+ in a distorted octahedral coordination are present in all samples. One can conclude from the Mossbauer parameters that iron is present in a very broad site distribution, which is characteristic of an a morphous structural neighborhood. The precipitation of crystalline K4Nb6O17 and the ferroelectric KNbO3 crystals was confirmed by X-ray powder diffrac tion in the samples with x = 40 and 50 mol%, respectively. The infrared and Raman scattering spectroscopy results suggest that the increase of the rat io Nb2O5/P2O5 leads the niobium to sites of octahedral symmetry and consequ ently to the formation of ferroelectric KNbO3, as seen by X-ray diffraction analysis. (C) 2000 Elsevier Science Ltd. All rights reserved.