title: Tuning the thermoelectric properties of A-site deficient SrTiO3ceramics by vacancies and carrier concentration.
abstract: Ceramics based on Sr0.8La0.067Ti0.8Nb0.2O3-δhave been prepared by the mixed oxide route. The La1/3NbO3component 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 Ti1-xNbxO2-ysecond 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 × 1021cm-3. 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.
authors.affiliation: School of Materials, University of Manchester, Manchester M13 9PL, UK. Robert.Freer@manchester.ac.uk.
authors.forename: Deepanshu
authors.initials: D
authors.lastname: Srivastava
authors.affiliation: School of Materials, University of Manchester, Manchester M13 9PL, UK. Robert.Freer@manchester.ac.uk.
authors.forename: Colin
authors.initials: C
authors.lastname: Norman
authors.affiliation: School of Materials, University of Manchester, Manchester M13 9PL, UK. Robert.Freer@manchester.ac.uk.
authors.forename: Feridoon
authors.initials: F
authors.lastname: Azough
authors.affiliation: Laboratoire CRISMAT, 14050 Caen Cedex, France.
authors.forename: Marion C
authors.initials: MC
authors.lastname: Schäfer
authors.affiliation: Laboratoire CRISMAT, 14050 Caen Cedex, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Guilmeau
authors.affiliation: SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK.
authors.forename: Demie
authors.initials: D
authors.lastname: Kepaptsoglou
authors.affiliation: SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK.
authors.forename: Quentin M
authors.initials: QM
authors.lastname: Ramasse
authors.affiliation: CNR-IMM, Strada VIII, 5, 95121 Catania, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Nicotra
authors.affiliation: School of Materials, University of Manchester, Manchester M13 9PL, UK. Robert.Freer@manchester.ac.uk.
authors.forename: Robert
authors.initials: R
authors.lastname: Freer