New solid solutions Ca3B2 + xSi1–xO8–x/2

New solid solutions Ca 3 B 2 + x Si 1– x O 8– x /2 based on monoclinic borosilicate β-Ca 3 B 2 SiO 8 are prepared using crystallization from a melt. The homogeneity range of solid solutions (0 < х ≤ 0.86) is determined and the thermal behavior of solid solution Ca 3 B 2.4 Si 0.6 O 7.8 is studied using high-temperature X-ray powder diffraction: a reversible β ↔ α polymorphic transition is discovered in the solid solution ( х = 0.4) at 550°C, decomposition begins in the solid state above 940°C with the formation of CaSiO 3 . The thermal expansion of both modifications is anisotropic: 20–540°C (α 11 = 17, α 22 = 16, α 33 = 0, α V = 32 × 10 −6 °C −1 ) and 560–900°C (α 11 = 15, α 22 = 24, α 33 = 3, and α V = 42 × 10 −6 °C −1 ).