Density Functional Theory Study of Electronic Structures in Lithium Silicates: $Li_2SiO_3$ and $Li_4SiO_4$

Abstract

Lithium silicates, such as $Li_2SiO_3$ and $Li_4SiO_4$, are considered as favorable candidates for the tritium breeding materials of a nuclear fusion reactor. Their bulk electronic properties and mechanics are important for the tritium behavior and tritium breeding blanket designs. We have studied the structural and electronic properties of $Li_2SiO_3$ and $Li_4SiO_4$ bulks using density functional theory (DFT) within generalized gradient approximation (GGA). The calculated crystal parameters are well consistent with the experimental results. The electronic band energy calculations show that $Li_2SiO_3$ and $Li_4SiO_4$ are insulators with a band gap of about 5.36 and 5.53 eV, respectively. Their valence band properties are mainly determined by the oxygen 2$p$ orbital electrons. The two types of oxygen atoms, nonbridging oxygen (NBO) atoms and bridging oxygen (BO) atoms, in $Li_2SiO_3$ reveal significantly different electron distribution of oxygen 2$p$ orbital. The Si 3$s$ and 3$p$ hybridization is observed in $Li_2SiO_3$, but not in $Li_4SiO_4$. In both lithium silicates, the electronic density increases more steeply around $Li$ and $Si$ atom sites compared with that around $O$ atoms. Additionally, the mechanical properties of both lithium silicates were calculated and discussed first time.