Structure and microwave dielectric properties of Li(Al1-xLix)SiO4-x ceramics

Li(Al1-xLix)SiO4-x (x = 0.005, 0.01, 0.015, and 0.02) ceramics were synthesized via a traditional solid phase reaction method with different sintering temperatures. To determine the positions occupied by Li+ in the lattice, the defect formation energies and total energies of various sites of LiAlSiO4 (LAS) occupied by Li+ were examined, and the energy of LAS systems were calculated using density functional theory of first-principle with the CASTEP module. The results demonstrated that the Al-sites occupied by Li+ had the lowest formation energies and total energy, so Li + should substitute Al3+. The impacts of replacing Al3+ with Li+ on the bulk density, sintering properties, phase composition, microstructure, and microwave dielectric properties of Li(Al1-xLix)SiO4-x (0 = x ≤ 0.02) ceramics were thoroughly studied. With Li+-doping, the sintering temperature decreased from 1300 °C (x = 0) to 1175 °C (x = 0.02), while the Q × f and τf values of LAS ceramics significantly increased. The Li(Al0.99Li0.01)SiO3.99 ceramic was fully sintered at 1250 °C for 10 h to obtain excellent microwave dielectric properties: εr = 3.49, Q × f = 51,358 GHz, and τf = −51.48 × 10−6 °C−1.