An X-ray diffraction, magnetic susceptibility and spectroscopic studies of Yb 2− xCr xO 3

Abstract

Polycrystalline samples with general formula Yb 2− x Cr x O 3 (0< x<0.03), obtained by sol–gel method and analyzed by X-ray diffraction, formed solid solutions over all the mentioned range. Cr showed a maximum solubility of 2.8 mol% in Yb 2O 3 sesquioxide at 1000 °C. A preferential substitution of Cr 3+ ions over two cationic sites, 8 b and 24 d in the space group Ia-3 was found. The lattice parameters a are found to vary linearly (10.4402(4) Å < a<10.4372(1) Å) with the composition x. The two independent atoms Yb/Cr have octahedral coordination; however, the degrees of distortion of their coordination polyhedron are different. Replacing Yb 3+ by Cr 3+ introduces slight changes in the atomic coordinates leading to an increase of the mean cation-anion distances. The ability of Raman spectroscopy to detect changes in local coordination is utilized. A pseudo-tetrahedral coordination for the Cr 3+ in the 24 d site was found. Magnetic susceptibility measurements of all samples were done in a temperature range of 2–50 K. For T<37 K, the inverse paramagnetic susceptibilities depend linearly on temperature. However, in the high-temperature region, for T>37 K, the inverse paramagnetic susceptibilities are non-linear versus temperature. This deviation from the Curie–Weiss behaviour was discussed.