Structural studies of KNbO3 in niobate glass-ceramics

Abstract

Potassium niobophosphate glasses and glass-ceramics of the family [xNb2O5·(50−x)P2O5·50K2O]:yFe2O3 were studied by X-ray powder diffraction, Mössbauer, infrared and Raman scattering spectroscopy. For the potassium–phosphate samples [50P2O5–50K2O], the iron oxide presents a network forming behavior for 5mol% of Fe2O3 doping. From our Mössbauer analysis, high spin Fe2+ and Fe3+ in a distorted octahedral coordination are present in all samples. One can conclude from the Mössbauer parameters that iron is present in a very broad site distribution, which is characteristic of an amorphous structural neighborhood. The precipitation of crystalline K4Nb6O17 and the ferroelectric KNbO3 crystals was confirmed by X-ray powder diffraction in the samples with x=40 and 50mol%, respectively. The infrared and Raman scattering spectroscopy results suggest that the increase of the ratio Nb2O5/P2O5 leads the niobium to sites of octahedral symmetry and consequently to the formation of ferroelectric KNbO3, as seen by X-ray diffraction analysis.