Ab initio investigations of electronic structure, optical transparency, and elastic properties in X3Al2Si3O12 (X = Ca, Mg)

A series of ab initio simulations were performed to investigate the electronic, transparent, and elastic properties of Ca3Al2Si3O12 and Mg3Al2Si3O12 which have potential applications in lithography optics, lenses and phosphor materials. From the simulated electronic structure and optical properties, we found that the theoretical transmittance of both compounds reaches 90% above 198 nm in the UT region. The bulk modulus and shear modulus of Ca3Al2Si3O12 were calculated to be 181.41 and 115.84 GPa, respectively. The anisotropy in elastic properties along different crystallographic direction were found greater in Ca3Al2Si3O12 than that in Mg3Al2Si3O12. The distinct dodecahedral coordinated Ca and Mg in the crystal structures result in the maximum Young's modulus existing in different direction, which is along [1 0 0] direction for Ca3Al2Si3O12 but [1 1 1] direction for Mg3Al2Si3012. Our theoretical investigations provided a basic understanding on the materials design of Ca3Al2Si3O12 and Mg3Al2Si3O12.