Effect of Mg(II) and Na(I) Doping on the Electronic Structure and Mechanical Properties of Kaolinite

Abstract

Because kaolinite has multiple defects, it is very important to study the effect of different doped cations on the electronic structure and mechanical properties of kaolinite (Al4Si4O18H8) from the microscopic point of view with the first-principle calculation method. The results exhibited that the doping of Mg(II) and Na(I) makes the ion bond and layer spacing of kaolinite crystal change, and the bond length of the chemical bond between the doped and O atom is positively related to the atomic radius of the doped cations. Compared with undoped kaolinite crystal, the band gap width of the Mg-doped and Na-doped kaolinite crystal was larger, but the typical insulator characteristics were still maintained. Compared with undoped kaolinite crystal, Mg-doped and Na-doped kaolinite crystal had more electron transfer to O, while the Mg–O bond and Na–O bond had more ionic bond properties and less covalent bond composition than the Al–O bond. Finally, the elastic properties of undoped, Mg-doped, and Na-doped kaolinite crystal were further analyzed by calculating the elastic constant matrix. The influence of doping Mg(II) and Na(I) on C11 and C22 was greater than that on C33, indicating that doping had a greater influence on the stiffness in the direction of the parallel crystal plane. The doping of Mg(II) and Na(I) weakened the rigidity of kaolinite crystal materials and improved the plasticity and ductility of the materials. The atom-scale information provided a basis for explaining the mechanical behavior of kaolinite and is expected to provide guidance for solving the deformation problems in soft rock roadways.