Thermal expansion behavior of SrSiO₃ and Sr₂SiO₄ determined by high-temperature X-ray diffraction and dilatometry

Strontium silicates are widely known as high thermal expansion materials, especially from glass ceramic sealing applications. However, the thermal expansion behavior of the pure crystalline phases is still unknown. Hence, SrSiO₃ and Sr₂SiO₄ were characterized with dilatometry and high-temperature X-ray diffraction. The measured coefficients of thermal expansion (CTE) of Sr₂SiO₄ are strongly anisotropic and depending on the crystallographic direction vary between 3.9 and 16.6 × 10⁻⁶ K⁻¹. SrSiO₃ has a somewhat higher isotropy of thermal expansion than Sr₂SiO₄. The CTE in the respective crystallographic directions differs by only 1.9 × 10⁻⁶ K⁻¹. The mean CTE is between 10.9 and 12.8 × 10⁻⁶ K⁻¹ for SrSiO₃ and Sr₂SiO₄, respectively. A comparison of the Sr-phases with Ba- and Ca-phases with the same stoichiometry is given with respect to the crystal structures and the CTE.