Multicomponent flux growth and composition control of Cu₂MnBO₅:Ga ludwigites

To reach the concentration phase boundary between antiferromagnetic Cu2GaBO5 and ferrimagnetic Cu2MnBO5 ludwigites, solid solutions Cu2Mn1−xGaxBO5 (x = 0.05, 0.1, 0.15, 0.175) were grown by the flux technique using a multi-component solvent based on Bi2Mo3O12 with the addition of Na2B4O7 which significantly influenced the crystal formation and cation composition of the studied compounds. The content of the flux system was corrected taking into account the earlier established relationship of the partition coefficients of Mn2O3 and Ga2O3. The influence of the solvent components on the ludwigite crystallization was analyzed. The maximum size of the grown crystal was 1 × 1 × 4 mm3. The structure and cation composition of the grown compounds were studied using X-ray (X-ray diffraction, EDX (energy-dispersive X-ray spectroscopy)) and vibrational (Raman) spectroscopy techniques. The phase boundary of Cu2MnBO5–Cu2GaBO5 was found to be in the concentration range of x = 0.15–0.175, corresponding to a change in the monoclinic axis direction and a leap in the lattice parameters. The symmetry evolution of metal–oxygen octahedra for four nonequivalent cation positions was analyzed, and the unique crystal structure of Cu2MnBO5 demonstrated high rigidity relative to the introduction of Ga3+ cations. The polarized Raman spectra of monoclinic ludwigites were obtained and studied for the first time. A comparison of the spectra of the studied samples in both phases and orthorhombic ludwigites was made. A number of spectral features due to the monoclinic distortions in the crystal were found. In agreement with the Raman experiment, the concentration phase boundary was close to 0.15.