Thermal Expansion of REE3BSi2O10 (REE = Nd, Eu, Gd) Borosilicates

Three borosilicates with the general formula of REE₃BSi₂O₁₀ (REE = Nd, Eu, Gd) were obtained by the high-temperature solid-state synthesis and studied by powder high-temperature X-ray diffraction (HTXRD) in the temperature range from 30 up to 1050°C. The HTXRD study showed that these borosilicates (orthorhombic, Pbca space group) have similar, nearly isotropic thermal expansion in the whole temperature range; the average coefficients of thermal expansion (CTE) were: 〈α_a〉 = 9.6, 〈α_b〉 = 8.3 and 〈α_c〉 = 8.7 × 10^–6°С^–1, with (α_max – α_min) ≤ 1.2 × 10^–6°С^–1. The average volume CTE insignificantly decreases with increasing the cation size from 27.2 for Eu and 27.0 for Gd down to 25.8 × 10^–6°С^–1 for Nd compound while the unit cell volume increases with increasing the REE cation radii in the REE₃BSi₂O₁₀ series.