Crystal Structures of Ilmenite Type LiNbO<sub>3</sub> and NaNbO<sub>3</sub>

Abstract

Crystal structures of ilmenite type NaNbO3 and LiNbO3, which were prepared by low temperature hydrothermal and ionexchange reactions respectively, were refined by the X-ray powder Rietveld method. Final R-factors were Rwp=16.9, Rp=12.2, RB=6.1% for NaNbO3 and Rwp=13.9, Rp=11.1, RB=5.7% for LiNbO3. The mean Nb-O distances of both ilmenite type compounds agreed with those of their corresponding stable phases. The mean Na-O distance of the ilmenite type NaNbO3 was as large as that of the spinel type Na2WO4, while, the mean Li-O distance in the ilmenite type LiNbO3 was slightly larger than that of the LiNbO3 type LiNbO3 or other compounds containing LiO6 octahedra. Structural refinement of other ilmenite type compounds of MgTiO3, CdTiO3, NaSbO3, NaBiO3 and KSbO3 was also carried out by the X-ray powder Rietveld method. Stability field of ilmenite type compounds, ABO3, was discussed on the basis of volumes of the AO6 and BO6 octahedra.