Gallium Composition-Dependent Structural Phase Transitions in HoFe3–xGax(BO3)4 Solid Solutions: Crystal Growth, Structure, and Raman Spectroscopy Study

Single crystals of solid solutions of HoFe 3– x Ga x (BO 3 ) 4 with x = 0, 0.5, 1, 1.5, and 3 were obtained using flux synthesis. The conditions of the synthesis are described in detail. The structural properties of each of the synthesized samples were studied using X-ray powder diffraction analysis at several temperature points (303, 403, and 503 K). The structural parameters of the obtained samples and the “pure” compounds HoFe 3 (BO 3 ) 4 and HoGa 3 (BO 3 ) 4 were compared. The Raman spectra of the obtained solid solutions HoFe 3– x Ga x (BO 3 ) 4 were studied in a wide temperature range ( T = 10–400 K). The vibrational spectra and eigenvectors of the HoFe 3 Ga(BO 3 ) 4 and HoGa 3 (BO 3 ) 4 in R 32 phase and HoFe 3 Ga(BO 3 ) 4 in P 3 1 21 phase were calculated within density functional theory. The features of the Raman spectra of HoFe 2 Ga(BO 3 ) 4, HoFe 2.5 Ga 0.5 (BO 3 ) 4, HoFe 3 (BO 3 ) 4 crystals associated with the R 32 → P 3 1 21 structural phase transition, which have a strong dependence on the degree of substitution x, were investigated. Peculiarities of the Raman spectra, which are associated with magnetic ordering in HoFe 1.5 Ga 1.5 (BO 3 ) 4, HoFe 2 Ga(BO 3 ) 4, and HoFe 2.5 Ga 0.5 (BO 3 ) 4 crystals, were detected.