New double holmium borates: Rb3HoB6O12 and Rb3Ho2B3O9

Abstract Double borates Rb3HoB6O12, Rb3Ho2B3O9 were newly synthesized by the sol–gel method and with solid state reactions. The crystal structures were determined from powder X-ray diffraction data. Rietveld's refinement of Rb3HoB6O12 showed the following: R32, a = 13.4078 (2) A, c = 30.3398 (4) A, Z = 15. Rb3Ho2B3O9 species revealed: Pna21, a = 8.7139 (1) A, b = 9.5760 (2) A, c = 12.22335 (1) A, Z = 2. Rb3HoB6O12 and Rb3Ho2B3O9 incongruently and congruently melted at 818 °C and 908 °C, respectively. The phase transition for Rb3HoB6O12 was established at 715 °C. The existence of B5O10 group in Rb3HoB6O12 crystal structure was confirmed by an IR analysis.