Phase Transformations in Dicalcium Silicate: II, TEM Studies of Crystallography, Microstructure, and Mechanisms

The crystallography, microstructures, and phase transformation mechanisms in dicalcium silicate (Ca 2 SiO 4 ) were studied by TEM. Three types of superlattice structures were observed in the α′ L and β phases. Almost all β grains were twinned and strained. Symmetry‐related domain structures inherited from previous high‐temperature transformations were observed in β grains. Both the α→α′ H and α′ L →β transformations were considered to be ferroelastic, and spontaneous strains were calculated. In terms of the crystal structures, the major driving force for the β→γ transformation is proposed to be strains and cation charge repulsions in the β structure. This mechanism can be displacive, but it needs to overcome a comparatively high energy barrier.