Synthesis, anion order and magnetic properties of RVO3−xNx perovskites (R = La, Pr, Nd; 0 ≤ x ≤ 1)

Abstract

The rare earth vanadium oxynitride perovskites RVO_3−xN_x (R = La, Pr, Nd; 0 ≤ x ≤ 1) have been prepared by treatment of RVO₄ precursors in NH₃. The ammonolysis reactions proceed through an initial reduction of RVO₄ precursors to RVO₃ perovskites that are progressively nitrided and reoxidised to RVO_3−xN_x materials with varying proportions of V⁴⁺/V³⁺. Variable temperature neutron diffraction studies show that NdVO₂N and PrVO_2.24N_0.76 have orthorhombic Pbnm symmetry between 3.5 and 300 K, but LaVO_2.11N_0.89 undergoes a broad Pbnm to Rc structural transition over this temperature range. In LaVO_3−xN_x samples the proportion of the Rc phase at room temperature increases with the nitrogen content. The partial anion order indicative of planes of cis-VN₂ chains found in NdVO₂N is also present in PrVO_2.24N_0.76, and is thus robust to the disorder created by non-stoichiometry. Magnetic measurements reveal spin freezing transitions at low temperatures in LaVO_2.09N_0.91 and PrVO_2.24N_0.76, but NdVO₂N is paramagnetic.