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), α_c = 7.56(13), α_V = 26.74(30) × 10^–6°C^–1 at 30°C; and α_a = 14.44(12), α_c = 10.74(13), α_V = 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.