Tuning the thermoelectric properties of A-site deficient SrTiO₃ ceramics by vacancies and carrier concentration

Abstract

Ceramics based on SrLaTiNbO have been prepared by the mixed oxide route. The LaNbO component generates ∼13.4% A-site vacancies; this was fixed for all samples. Powders were sintered under air and reducing conditions at 1450 to 1700 K; products were of high density (>90% theoretical). Processing under reducing conditions led to the formation of a TiNbO second phase, core-shell structures and oxygen deficiency. X-ray diffraction (XRD) confirmed a simple cubic structure with space group Pm3[combining macron]m. Transmission electron microscopy revealed a high density of dislocations while analytical scanning transmission electron microscopy at atomic resolution demonstrated a uniform distribution of La, Nb and vacancies in the lattice. X-ray photoemission spectroscopy and thermogravimetry showed the oxygen deficiency (δ value) to be ∼0.08 in reduced samples with enhanced carrier concentrations ∼2 × 10 cm. Both carrier concentration and carrier mobility increased with sintering time, giving a maximum figure of merit (ZT) of 0.25. Selective additional doping by La or Nb, with no additional A site vacancies, led to the creation of additional carriers and reduced electrical resistivity. Together these led to enhanced ZT values of 0.345 at 1000 K. The contributions from oxygen vacancies and charge carriers have been investigated independently.

Graphene/Strontium Titanate: Approaching Single Crystal–Like Charge Transport in Polycrystalline Oxide Perovskite Nanocomposites through Grain Boundary Engineering

“…Single crystals (SC) are indicated with red dashed lines and polycrystalline samples (PC) are indicated with green solid lines. Literature sources: lanthanum doped STO single crystal (LSTO‐SC), reduced STO single crystal (RSTO‐SC), niobium doped STO single crystal (NSTO‐SC), polycrystalline lanthanum doped STO (LSTO‐PC), polycrystalline lanthanum and niobium doped STO (LNSTO‐PC) …”

Anisotropy and enhancement of thermoelectric performance of Sr0.8La0.067Ti0.8Nb0.2O3−δceramics by graphene additions

“…4,6 We have previously shown that controlled doping on Sr/Ti sites of SrTiO 3 (STO), in addition to controlled vacancy formation within the system, can introduce signicant numbers of charge carriers. 15,16 Cationic vacancies in donor doped STO have been shown to increase carrier concentration and generate oxygen vacancies under reducing environment. These point defects play a crucial role in reducing thermal conductivity by scattering of phonons.…”

Enhancement of Thermoelectric Performance of Sr0.9‐xNd0.1Ti0.9Nb0.1O3 Ceramics by Introducing Sr Vacancies

“…So introducing Sr vacancies demonstrates a valid method for raising the TE performances of SrTiO 3 ‐based materials. In the literature, the contents of Sr vacancies were often related with the substitution contents which resulting in equivalent doping, and most reports were made on single‐doped samples . The physical mechanisms how Sr vacancies influence thermoelectric properties are not very clear until now.…”