Structure change in strontium oxide-doped dicalcium silicates

A series of strontium-bearing dicalcium silicate (Ca₂SiO₄) solid solutions (C₂S(ss)), (Sr_xCa_1-x)₂SiO₄ with 0.02 ≤ x ≤ 0.10, was prepared and examined by powder X-ray diffractometry. These crystals, heated in the stable-temperature region of the α phase and then quenched in water, were composed of the β phase, with x ≤ 0.08, and the α′_L and β phases, with x = 0.10. With increasing x, the unit-cell axes of the β phase expanded and the β angle became small with eventual increase in the unit-cell volume. The Rietveld analysis of the β-C₂S(ss) with x = 0.08 showed that the Sr²⁺ ions preferentially occupied the seven-coordinated site rather than the eight-coordinated site. This site preference, which was originally established in the parent α-phase structure, seemed to cause the systematic change in the cell dimensions.