Effect of Sc³⁺ doping on the structure and electrical properties of NBT-based oxygen-ion conductor

Abstract Sc 3+ was chosen as the dopant, and two series of samples, Na 0.5 Bi 0.49-x Sc x TiO 3- δ (abbreviated as x Sc-Bi, x = 0–0.05) and Na 0.5 Bi 0.49 Ti 1-x Sc x O 3- δ (abbreviated as x Sc-Ti, x = 0–0.07), were synthesized via the solid-state method. The influence of Sc 3+ doping at distinct lattice sites on the structural, microstructural, and electrical properties of Na 0.5 Bi 0.49 TiO 3- δ oxygen-ion conductors was systematically investigated. The results reveal that at low doping concentrations (x ≤ 0.02), Sc 3+ tends to occupy the Bi 3+ sites, while at higher concentrations (x > 0.02), it favors the Ti 4+ sites. Sc 3+ occupies the Bi 3+ sites and inhibits grain growth, while it occupies the Ti 4+ sites and facilitates grain growth. In terms of grain conductivity, the x Sc-Bi series samples exhibit superior performance. In terms of grain boundary conductivity, Sc 3+ doping significantly reduces grain boundary resistance. At low doping concentrations, the x Sc-Bi series exhibits higher grain boundary conductivity than the x Sc-Ti series; however, at higher concentrations, the x Sc-Ti series outperforms the x Sc-Bi series. Given that grain boundary resistance dominates the total resistance, the x Sc-Ti series samples also exhibit higher total conductivity.