Study on structures and dielectric properties of (Li_xNb _1-x)_0.25Ti_0.75O₂ based on molecular simulation

Microwave dielectric ceramics are widely used in microwave communication, because of their favorable dielectric properties. Many experimental researches for the new ceramic materials (Li_xNb_1-x) _0.25Ti_0.75O₂(LNT, x=0.2, 0.4, 0.6) have been carried out. However, few of computer simulations have been implemented, due to their complex structures of a solid solution. In this present, molecular simulation was applied to research on structures and dielectric properties. The supercell structures of the LNT were built by experimental X-ray diffraction spectra and optimized by using density functional theory, to solve the complex structure problem of the solid solution. Based on the optimized supercells, the band structures and optical permittivity were also calculated. Infrared spectrum was computed using density functional perturbation theory to obtain the dielectric constant. The simulation results are corresponded well with experiments. Optimized structures show that the substitution of lithium and niobium for titanium in rutile causes lattice distortion. The results of infrared spectrum reveal that dielectric constant decreases if value of x is increased.