The structure and thermoelectric properties of tungsten bronze Ba6Ti2Nb8O30

DOI: 10.1063/1.5119962

Authors: Dongting Jiang (University of Manchester) , Dursun Ekren (University of Manchester) , Feridoon Azough (University of Manchester) , Sarah Day (Diamond Light Source) , Kan Chen (Queen Mary University of London) , Amit Mahajan (Queen Mary University of London) , Demie M. Kepaptsoglou (SuperSTEM Laboratory, STFC Daresbury Campus; University of York) , Quentin M. Ramasse (SuperSTEM Laboratory, STFC Daresbury Campus; University of Leeds) , Michael J. Reece (Queen Mary University of London) , Robert Freer (University of Manchester)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Applied Physics , VOL 126

State: Published (Approved)
Published: September 2019

Abstract: Tungsten bronze (TB) structured materials have attracted attention as possible thermoelectrics because of their complex crystal structure. In this work, a new thermoelectric ceramic with a tetragonal tungsten bronze (TB) structure, Ba6Ti2Nb8O30 (BTN), was prepared by the conventional mixed oxide route with some samples processed by Spark Plasma Sintering (SPS). The addition of MnO enabled the fabrication of high density BTN ceramics at a low sintering temperature of 1580 K in air and by SPS. All samples were annealed in a reducing atmosphere after sintering. X-ray diffraction showed that Ba6Ti2Nb8O30 crystallizes with tetragonal symmetry (P4bm space group). High angle annular dark field-electron energy loss spectroscopy analysis confirmed the proposed crystal structure and provided exact elemental distributions in the lattice, showing higher concentrations of Ti in the 2b lattice sites compared to the 8d lattice sites. XPS showed the presence of two spin-orbit double peaks at 207.7 eV in the reduced BTN samples, confirming the presence of Nb4+ ions. By the use of a sintering aid and optimization of the processing parameters, the ceramics achieved a high power factor of 280 μW/m K2 at 873 K. The BTN ceramics showed phonon-glass-type thermal conduction behavior with a low thermal conductivity of 1.7–1.65 W/m K at 300–873 K. A thermoelectric figure of merit (ZT) of 0.14 was achieved at 873 K. This ZT value is comparable with results for many TB thermoelectrics. However, BTN has the advantage of much easier processing.

Journal Keywords: Electron energy loss spectroscopy; Oxides; Transmission electron microscopy; Ceramics; Sintering; X-ray diffraction; Thermal conductivity; Thermoelectric effects; Phonons; Thermodynamic states and processes

Subject Areas: Physics, Materials


Instruments: I11-High Resolution Powder Diffraction

Added On: 07/10/2019 14:10

Documents:
gjj4h4gg4.pdf

Discipline Tags:

Quantum Materials Hard condensed matter - electronic properties Ceramics Physics Materials Science Thermoelectrics

Technical Tags:

Diffraction X-ray Powder Diffraction