Flux Growth and Raman Spectroscopy Study of Cu2CrBO5 Crystals

https://doi.org/10.3390/cryst13101415

Multicomponent flux systems based on both Li₂WO₄-B₂O₃-Li₂O-CuO-Cr₂O₃ and Bi₂O₃-MoO₃-B₂O₃-Na₂O-CuO-Cr₂O₃ were studied in order to grow Cu₂CrBO₅ crystals. The conditions for Cu₂CrBO₅ crystallization were investigated by varyingthe component ratios, and the peculiarities of their interaction were characterized by studying the formation sequence of high-temperature crystallizing phases. Special attention was paid to the problem of Cr₂O₃ solubility. Phase boundaries between CuCrO₂, Cu₂CrO₄, and Cu₂CrBO₅ were considered. The crystal structure of the obtained samples was studied viasingle crystal and powder X-ray diffraction. The chemical composition of the grown crystals was examined using the EDX technique. Anactual ratio of Cu:Cr = 1.89:1.11 was found for Cu₂CrBO₅ grown from the lithium-tungstate system, which showed a small deviation from 2:1, implying the presence of a part of bivalent Cr²⁺ in the samples. Anomalies in the thermal dependence of magnetization were analyzed and compared with the previously obtained data for Cu₂CrBO₅. The anomaly at T_C ≈ 42 K and the antiferromagnetic phase transition at T_N ≈ 119 K were considered. Polarized Raman spectra of Cu₂CrBO₅ were obtained for the first time, and a comparative analysis of the obtained data with other monoclinic and orthorhombic ludwigites is presented. Along with the polarized room temperature spectra, the thermal evolution of Raman modes near the antiferromagnetic phase transition temperature T_N ≈ 119 K is provided. The influence of the magnetic phase transition on the Raman spectra of Cu₂CrBO₅ is discussed.