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

Evgeniya Moshkina, Svetlana Krylova, Irina Gudim, Maxim Molokeev, Vladislav Temerov, M.S. Pavlovskii, Alexander Vtyurin, and Alexander Krylov. Crystal Growth & Design. doi:10.1021/acs.cgd.9b01387.

Single crystals of solid solutions of HoFe3-xGax(BO3)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 synthesised samples were studied using X-ray powder diffraction analysis at several temperature points (303 K, 403 K, 503 K). The structural parameters of the obtained samples and the “pure” compounds HoFe3(BO3)4 and HoGa3(BO3)4 were compared. The Raman spectra of the obtained solid solutions HoFe3-xGax(BO3)4 were studied in a wide temperature range (T = 10 ÷ 400 K). The vibrational spectra and eigenvectors of the HoFe3Ga(BO3)4 and HoGa3(BO3)4 in R32 phase and HoFe3Ga(BO3)4 in P3121 phase were calculated within density functional theory. The features of the Raman spectra of HoFe2Ga(BO3)4, HoFe2.5Ga0.5(BO3)4, HoFe3(BO3)4 crystals associated with the R32→P3121 structural phase transition, which have a strong dependence on the degree of substitution x, are investigated. Peculiarities of the Raman spectra, which are associated with magnetic ordering in HoFe1.5Ga1.5(BO3)4, HoFe2Ga(BO3)4, HoFe2.5Ga0.5(BO3)4 crystals, were detected.