Structure refinement and thermal properties of novel cubic borate Lu2Ba3B6O15.

Novel borate Lu 2 Ba 3 B 6 O 15 was prepared using a multi-step high-temperature solid-state synthesis. It crystallizes in the cubic system, Ia 3 ¯ space group, a = 14.18197(3) Å, V = 2852.396(18) Å3, Z = 8, and it is isostructural with Y 2 Ba 3 B 6 O 15. The crystal structure is described as a framework composed of the edge-sharing large irregular BaO 9 polyhedra. The intersecting tunnels in this framework are filled with the lutetium atoms. Two planar BO 3 triangles are connected to each other by the vertices, forming the isolated B 2 O 5 pyroborate groups. The Lu 2 Ba 3 B 6 O 15 thermal behavior was investigated by thermal analysis and high-temperature X-ray powder diffraction (HTXRD). The Lu 2 Ba 3 B 6 O 15 sample starts to melt at 1058 °C. As the temperature increases, the coefficient of linear expansion increases (α a = 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 BaO 9 polyhedra have the greatest influence on the Lu 2 Ba 3 B 6 O 15 expansion among those of the other constituent polyhedra. • Lu 2 Ba 3 B 6 O 15 is prepared using a multi-step solid-state synthesis. • The Lu 2 Ba 3 B 6 O 15 crystal structure is refined by the Rietveld method. • The Lu 2 Ba 3 B 6 O 15 thermal behavior is investigated over a wide range of temperatures. • The BaO 9 thermal deformations contribute the most to the Lu 2 Ba 3 B 6 O 15 expansion. [ABSTRACT FROM AUTHOR]