Rare earth niobium oxynitrides, LnNbON2-δ (Ln = Y, La, Pr, Nd, Gd, Dy): Synthesis, structure and properties

Ammonolysis of rare earth niobates of the type LnNbO(4) (Ln = Y, La, Pr, Nd, Gd, Dy) yields oxynitrides of different structures. When Ln = La, Nd and Pr, the structure is that of an orthorhombic perovskite of the general formula LnNbON(2). As the size of the rare earth decreases, the oxynitride has a nitrogen-deficient defect fluorite (Ln = Pr, Nd, Gd), or pyrochlore (Ln = Y) structure. The IR spectra of the oxynitrides and the corresponding oxides are significantly different. Thermogravimetric analysis suggests the formation of an intermediate phase wherein the N-2 molecule is attached to the oxide lattice above 400 degrees C and decomposes to give the oxide on heating in an oxygen atmosphere. Raman spectra of the intermediate phases show evidence for the N N stretching vibration. Gadolinium niobium oxynitride is found to be paramagnetic. (C) 2011 Elsevier Ltd. All rights reserved.