Crystal structures and thermal expansion of Yb₂Si₂O₇–Gd₂Si₂O₇ solid solutions

Solid solutions within the Yb₂Si₂O₇–Gd₂Si₂O₇ system were synthesized by a solid state reaction route and characterized for their structural and thermal properties. Incorporation of Gd₂Si₂O₇ into Yb₂Si₂O₇ resulted in multiple phase transformations, with the solid solutions exhibiting the monoclinic β-RE₂Si₂O₇, monoclinic γ-RE₂Si₂O₇, and orthorhombic δ-RE₂Si₂O₇ crystal structures. The stability of crystal structures with additions of Gd₂Si₂O₇ are attributed to space filling and minimization of molar volume. The thermal expansion coefficients (CTE) of the β and γ structures were largely unchanged by the addition of Gd₂Si₂O₇ to the lattice, although the orthorhombic Yb₂Si₂O₇–Gd₂Si₂O₇ solid solution exhibited slightly less anisotropy in CTE of the lattice directions (25°C–1500°C) than undoped orthorhombic δ-Gd₂Si₂O₇.