Thermal Expansion of Oxoborogermanate Sm14(GeO4)2(BO3)6O8

Thermal expansion of samarium oxoborogermanate Sm14(GeO4)2(BO3)6O8 is studied by the method of high temperature powder X-ray diffraction in the temperature range of 30–1200°C. The coefficients of thermal expansion are calculated: α11 = 9.59(12), αc = 7.56(13), αV = 26.74(30) × 10–6°C–1 at 30°C; and αa = 14.44(12), αc = 10.74(13), αV = 39.61(28) × 10–6 °C–1 at 1200°C. A structural interpretation of the anisotropy of thermal expansion is carried out. With increasing temperature, the degree of anisotropy remains practically unchanged, the structure expands minimally along the c axis, and maximally in the ab plane, perpendicular to the preferred orientation of the BO3 triangles in the crystal structure. The melting point of Sm14(GeO4)2(BO3)6O8 is clarified.