Synthesis, structure and magnetic properties of R–W–O–N (R=Nd and Eu) oxynitrides

Neodymium and europium tungsten oxynitrides have been synthesized by the nitridation of corresponding R2W2O9 precursor oxides, in ammonia flow at 1173 K during 24 h. The obtained polycrystalline neodymium oxynitride phase, with NdWO3.05N0.95 composition, crystallizes with the tetragonal symmetry of the scheelite-type structure, space group S.G. image (#88). The analogous europium derivative, with formula EuWO1.58N1.42, presents the cubic perovskite-type structure, S.G. image (# 221). Unit-cell parameters, a=5.255(1) Å, c=11.399(3) Å, and a=3.976(3) Å, have been established from Rietveld refinements of collected X-ray powder diffraction patterns for the Nd and Eu- oxynitrides, respectively. Magnetic susceptibility measurements show that NdWO3.05N0.95 behaves as paramagnetic in a wide range of temperature T ∼50–300 K. The downwards deviation from the Curie–Weiss law below 40 K reflects the splitting of the 4I9/2 ground state of Nd3+ experienced under the influence of a S4 crystal field CF potential, as the successful reproduction of the magnetic susceptibility χ−1m vs. T, using semi-empirical structure-derived CF parameters, indicates. EuWO1.58N1.42 is paramagnetic down to 20 K, and the measured effective magnetic moment 8.01 μB is indicative of the presence of Eu2+ in this oxynitride. The observed sudden jump in the magnetic susceptibility at 20 K and the value of 6 μB for the saturation moment is attributed to the onset of ferrimagnetic interactions in which the Eu2+ and W5+ sublattices appear to be involved.