Effect of aluminum substitution on structural, electronic and dielectric properties of cubic CaCu3Ti4O12 ceramics: A first-principles study

Abstract

The paper sheds light on the effect of Al substitution on structural, electronic and dielectric properties of cubic CaCu3Ti4O12 ceramics based on first principles method. The CaCu3Ti4-xAlxO12 (x = 0, 0.5, 1, 1.5 and 2) ceramics still keeps a cubic lattice, and the lattice constant decreases with Al concentration enhanced. Phonon dispersion curves show that the structures of CaCu3Ti4-xAlxO12 ceramics are thermodynamically stable at x ≤ 1. The CaCu3Ti4-xAlxO12 ceramics have magnetic semiconductor properties and the band gaps corresponding to the high symmetry point G increases with increasing Al concentration. It can be concluded that doping Al can increase the dielectric constant and electronic transition intensity of cubic CaCu3Ti4O12 ceramics, and reduce its energy loss. In the low energy region, the dielectric constant of CaCu3Ti3.5Al0.5O12 ceramics is about ten times that of cubic CaCu3Ti4O12 ceramics. The ratio of aluminum atoms to titanium atoms of 1:7 May be the best ratio. It can also be concluded that when A13+ replaces Ti4+ ions, A1 also acts as an electron acceptor to reduce the electron concentration of Ti4+ ions, leading to the generation of oxygen vacancies. These results will provide a theoretical basis for the design of high dielectric constant materials.