Thermal Expansion of Ba₃Lu(BO₃)₃ Borate

Abstract—In this study, Ba₃Lu(BO₃)₃ borate obtained by solid-phase synthesis is explored by high-temperature X-ray powder diffraction in the temperature range from 25 to 900°C. At room temperature, the compound expands slightly anisotropically (α_max/α_min = 1.2), and with an increase in temperature, the degree of anisotropy increases significantly (α_max/α_min = 6.9 at 900°C). The maximum expansion is observed along the crystallographic axis c (α_c = 10.45 × 10^–6°C^–1 at 25°C and 36.34 × 10^–6°C^–1 at 900°C), perpendicular to which the boron-oxygen triangles [BO₃] are located, and the minimum is in the plane where the triangles are located.