Effects of Zn doping on the mechanical and thermoelectric properties of calcium silicate hydrate

In this study, the mechanical properties, band structures, and density of states of calcium silicate hydrate (CSH) and Zn-doped CSH systems were calculated based on density functional theory. The thermoelectric properties were further analyzed using the BoltzTraP code. The results show that both CSH and Zn-doped CSH are mechanically stable. However, the incorporation of Zn reduces the mechanical performance of CSH. Electronic structure analysis indicates that Zn doping affects the electron distribution near the valence band maximum. It shifts the valence band maximum from the Γ point to the A point, thereby changing the system from a direct-band-gap material to an indirect-band-gap material. The thermoelectric calculations show that the maximum thermoelectric figure of merit, ZT_max, increases with increasing temperature. In addition, ZT_max under p-type doping is higher than that under n-type doping. Overall, although Zn doping weakens the mechanical properties of CSH to some extent, it can improve its thermoelectric performance and increase the ZT value of the system.

This study performed first-principles calculations using Quantum ESPRESSO. Structural optimization was conducted with the PBE functional, while band structures were calculated using the HSE06 hybrid functional. DFT-D3 dispersion correction and dipole correction were included. The elastic, transport, thermal conductivity, and thermoelectric figure of merit of CSH were evaluated using thermo_pw, BoltzTraP, the deformation potential method, and the Slack model.