Sr-doping effects on piezoelectric and dielectric properties of lead-free barium titanate via molecular dynamics approach

The study investigated the effects of Sr-doping on BaTiO₃ regarding the mean square displacement, diffusion coefficient, polarization-strain response, dielectric constant, and dielectric loss. Initially, increasing strontium doping up to 6% enhanced the mean square displacement (from 0.211 to 0.218 Ų) and the diffusion coefficient (from 0.361 to 0.380 nm²/ns) due to improved atomic mobility and lattice dynamics. However, further doping to 8% caused a decrease in both the mean square displacement and the diffusion coefficient, due to structural disorder and defects that impeded atomic movement. Similarly, the piezoelectric coefficient increased from 273.07 pC/N to 321.15 pC/N with 6% doping but declined to 308.65 pC/N at 8%. This indicated enhanced polarization at moderate doping levels but reduced performance due to excess impurities. The dielectric constant arose from 76 to 85 with 6% strontium but decreased to 80 at 8%, reflecting increased ferroelectric properties followed by structural degradation. Lastly, dielectric loss increased from 0.06 to 0.08 with 6% doping and then decreased to 0.073 at 8%. This suggested that while ionic mobility initially improved energy loss, excessive doping led to inefficiencies. Overall, optimal strontium doping enhanced the material's ferroelectric and piezoelectric properties, while excessive doping introduced detrimental effects.