Study on modulated structure of M3 polymorphic alite

M3 polymorphic alite was synthesized by the solid-state method. The pseudohexagonal subcell parameters and microstructure were studied by XRD and TEM. The pseudohexagonal subcell parameters of a=7.06 Å, b=7.07 Å, c=24.98 Å, α=90.02°, β=89.97°, γ=120.02° were calculated from XRD results. SAED and HRTEM reveal that there is one-dimensional commensurately modulated with a modulation vector of q =-0.17a*+0.17b*+1.17c* in M3 alite. The result indicates that the structure modulation in M3 is normal to (117)_R with the wavelength of 18.4 Å, which is 6 times greater than the spacing of (117)_R . The modulated structure could be observed in a HRTEM image as wavy contrast streaking. Further more, the SAED pattern and HRTEM image simulation work of M3 done using softwares of Crystalkit and Mactemps further verifies the aforementioned result. In addition, the modulated structure mechanism of M3 alite was studied, and it is concluded that the modulated structure is caused by the averaged position deviation of Ca²⁺ ion.