In-situ XANES and XRD studies of the phase transition of RCrO3+γ (R = Y, Pr, Nd, Gd and Dy; γ = 0 or 1) compounds

Abstract

In this paper, the growth kinetic of RCrO3+γ (R = Y, Pr, Nd, Gd and Dy; γ = 0 or 1) compounds obtained by co-precipitation method is investigated by in-situ X-ray diffraction (XRD) and in-situ X-ray absorption near edge spectroscopy (XANES) using synchrotron radiation. A structural phase transition from RCrO4 (tetragonal structure and space group I41/amd) to perovskite RCrO3 (orthorhombic structure and space group Pbnm) is observed as a function of the heating temperature. In addition, the analysis of the in-situ Cr-K-edge XANES spectra of precursor as a function of heating temperature are consistent with a change of oxidation state from Cr5+ to Cr3+. These results indicate that the temperature of the structural phase transition onset is dependent on the rare earth ion, which is also corroborated by thermogravimetric analysis (TGA). Moreover, magnetization measurements as a temperature function show ferromagnetic order for (Dy, Gd)CrO4 compounds, while (Nd, Pr)CrO4 and (Dy, Gd, Nd, Pr)CrO3 are antiferromagnetic with two magnetic phase transitions. These transitions are described as the highest temperature associated with the Cr–Cr antiferromagnetic order, while the other may be related to the magnetic order of the R-ions.