Structure refinement and thermal properties of novel cubic borate Lu2Ba3B6O15

Novel borate Lu2Ba3B6O15 was prepared using a multi-step high-temperature solid-state synthesis. It crystallizes in the cubic system, Ia3¯ space group, a = 14.18197(3) Å, V = 2852.396(18) Å3, Z = 8, and it is isostructural with Y2Ba3B6O15. The crystal structure is described as a framework composed of the edge-sharing large irregular BaO9 polyhedra. The intersecting tunnels in this framework are filled with the lutetium atoms. Two planar BO3 triangles are connected to each other by the vertices, forming the isolated B2O5 pyroborate groups. The Lu2Ba3B6O15 thermal behavior was investigated by thermal analysis and high-temperature X-ray powder diffraction (HTXRD). The Lu2Ba3B6O15 sample starts to melt at 1058 °C. As the temperature increases, the coefficient of linear expansion increases (αa = 5.7 at 25 °C and 8.9 × 10−6 C−1 at 800 °C). The Rietveld refinement of the HTXRD data showed that thermal deformations of the non-rigid BaO9 polyhedra have the greatest influence on the Lu2Ba3B6O15 expansion among those of the other constituent polyhedra.