Raman Spectroscopic Investigations of Dicalcium Silicate: Polymorphs and High‐Temperature Phase Transformations

Polymorphs and high‐temperature phase transformations of dicalcium silicate (Ca 2 SiO 4 ) are investigated on powdered samples, using Raman scattering techniques. Raman spectra at room conditions of pure γ‐ and β‐Ca 2 SiO 4 and stabilized β‐, α′ L ‐, and α‐Ca 2 SiO 4 are presented in the frequency range of 110–1100 cm −1 . Each polymorph can be identified by its Raman spectrum, even though strong similarities exist between the β, α′ L , and α phases. In‐situ high‐temperature Raman spectroscopic studies in the temperature range of 298–1433 K on heating and cooling also are reported, starting from γ‐Ca 2 SiO 4 . Modifications occurring in the Raman spectra recorded in the wavenumber range of 90–1000 cm −1 show up during heating, the irreversible γ→α′ L phase transformation. Coexistence of γ and α′ L grains is observed in the temperature range of 1091–1119 K at least. The differences observed between the γ‐Ca 2 SiO 4 and α′ L ‐Ca 2 SiO 4 Raman spectra suggest that this phase transformation is a reconstructive first‐order transition. The reversible α′ L ⇄β phase transformation also is described. Raman spectra of pure β and α′ L phases resemble each other. The transition occurs from 949 K, on cooling, to 960–988 K, on heating, with a hysteresis probably dependent on the thermal history of the starting product. From the Raman scattering observations, this phase transformation also is considered as a first‐order transformation and is probably of a displacive type.