title: Inversion Boundaries and Phonon Scattering in Ga:ZnO Thermoelectric Compounds.
abstract: We investigated the high-temperature thermoelectric properties of Ga:ZnO bulk compounds, synthesized using a simple and scalable solid-state process. The effects of a low gallium content (x ≤ 0.04 in Zn1-xGaxO1+x/2) on the structural features and electrical/thermal properties are reviewed. Transmission electron microscopy analyses showed that 2D, nonperiodic defects had formed from a doping content as low as x = 0.01 Ga. The structural description of these nanoscale interfaces is, for the first time, carefully investigated in such low-Ga-content samples by HAADF-STEM analyses combined with structural modeling. It was found that the formation of head-to-head inversion twin (h-IT) boundaries and tail-to tail inversion boundaries (t-IB) in the bulk compounds is responsible for strong phonon scattering, while maintaining relatively good electrical conductivity and thereby enhancing the thermoelectric properties. The absolute value of the Seebeck coefficient decreases abruptly from 475 μV/K for x = 0 down to 60 μV/K for x = 0.005 at 350 K. At the same time, the electrical resistivity drops from 1 ohm cm for x = 0 to 1.7 × 10-3ohm cm for x = 0.005. For higher Ga additions (x > 0.01), the increase in electrical resistivity is likely linked to the formation of interface defects at a larger extent in the wurtzite structure. The thermal conductivity also drops sharply with the increase in the Ga content from ∼33 W/m K for x = 0 to ∼8 for x = 0.04 at 350 K. This study is progress toward the synthesis of other thermoelectric materials where nanoscale interfaces in bulk compounds provide tremendous opportunities for further enhancing both the phonon scattering and the overall figure of merit.
authors.affiliation: Laboratoire CRISMAT , UMR 6508 CNRS/ENSICAEN, 6 bld Maréchal Juin, 14050 Caen Cedex, France.
authors.forename: Emmanuel
authors.identifier: http://orcid.org/0000-0001-7439-088X
authors.initials: E
authors.lastname: Guilmeau
authors.affiliation: Laboratoire CRISMAT , UMR 6508 CNRS/ENSICAEN, 6 bld Maréchal Juin, 14050 Caen Cedex, France.
authors.forename: Pablo
authors.initials: P
authors.lastname: Díaz-Chao
authors.affiliation: Laboratoire CRISMAT , UMR 6508 CNRS/ENSICAEN, 6 bld Maréchal Juin, 14050 Caen Cedex, France.
authors.forename: Oleg I
authors.initials: OI
authors.lastname: Lebedev
authors.affiliation: Department for Nanostructured Materials, Jožef Stefan Institute , Jamova 39, Ljubljana, Slovenia.
authors.forename: Aleksander
authors.initials: A
authors.lastname: Rečnik
authors.affiliation: Laboratoire CRISMAT , UMR 6508 CNRS/ENSICAEN, 6 bld Maréchal Juin, 14050 Caen Cedex, France.
authors.forename: Marion C
authors.initials: MC
authors.lastname: Schäfer
authors.affiliation: Université François Rabelais de Tours, CNRS, CEA , INSA CVL, GREMAN UMR 7347, IUT de Blois 15 rue de la chocolaterie, 41029 Blois Cedex, France.
authors.forename: Fabian
authors.initials: F
authors.lastname: Delorme
authors.affiliation: Université François Rabelais de Tours, CNRS, CEA , INSA CVL, GREMAN UMR 7347, IUT de Blois 15 rue de la chocolaterie, 41029 Blois Cedex, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Giovannelli
authors.affiliation: Department for Nanostructured Materials, Jožef Stefan Institute , Jamova 39, Ljubljana, Slovenia.
authors.forename: Mateja
authors.initials: M
authors.lastname: Košir
authors.affiliation: Department for Nanostructured Materials, Jožef Stefan Institute , Jamova 39, Ljubljana, Slovenia.
authors.forename: Slavko
authors.initials: S
authors.lastname: Bernik