Synergistically enhanced electrical transport properties of SrTiO3via Fermi level regulation and modulation doping

Abstract

SrTiO₃ has gained wide attention as an oxide thermoelectric material due to its high Seebeck coefficient and excellent high-temperature thermal stability. However, its intrinsic insulatory properties hinder its development as a thermoelectric material. Herein, we synergistically improved the electrical transport properties of SrTiO₃ by increasing carrier concentration and maintaining high carrier mobility via Fermi level regulation and modulation doping through co-doping and compositing. Nb and La co-doping notably heightened the carrier concentration and regulated the Fermi level in the conduction band, resulting in an enhanced ZT value from that of an insulator in SrTiO₃ to 0.033 in Sr_0.875La_0.125Ti_0.85Nb_0.15O₃ at 923 K. The subsequent TiB₂ compositing simultaneously improved carrier concentration (4.82 × 10¹⁷ cm³) and afforded high carrier mobility (3.55 × 10⁴ cm² V⁻¹ S⁻¹) in the Sr_0.875La_0.125Ti_0.85Nb_0.15O₃ + 4% TiB₂ sample at 923 K. The combination of synergistically improved carrier concentration and retained high carrier mobility resulted in an enhanced power factor (11.04 μW cm⁻¹ K⁻² at 923 K), maximum ZT (0.23 at 923 K) and average ZT (0.15 at 473–923 K) in Sr_0.875La_0.125Ti_0.85Nb_0.15O₃ + 4% TiB₂ through co-doping and compositing, which matches those of many excellent SrTiO₃-based materials. Our study demonstrated that the thermoelectric properties of SrTiO₃ could be improved via synergistically enhanced electrical transport properties through Fermi level regulation and modulation doping via co-doping and compositing, which will inspire further research on SrTiO₃ and other oxide thermoelectric materials with mediocre electrical transport properties.