Structural Studies of Jennite and 1.4 nm Tobermorite: Disordered Layering along the [100] of Jennite

Transmission electron microscopy of synthetic jennite reveals strong streaking in the electron diffraction patterns along the [100], along which dark-field imaging and lattice fringing confirm the presence of a layering with a striation-like morphology. The average periodicity between the layers is ∼35 Å; however, there is significant variation around this value in the range of 20-40 Å, which is in agreement with the range of periodicities that are associated with the streaking in the diffraction patterns. These results clearly demonstrate the presence of a layering along the [100] with a periodicity that varies spatially throughout the specimen, which results in the presence of a disordered modulated structure. We believe that the disorder is induced by frozen-in fluctuations in the local calcium:silicon ratio, which correspondingly results in fluctuations in the local structural order and periodicity of the modulated structure. Similar studies of 1.4-nm tobermorite have revealed streaking along the [100]; however, it was weak and diffuse.