title: The impact of charge transfer and structural disorder on the thermoelectric properties of cobalt intercalated TiS2.
abstract: A family of phases, CoxTiS2(0 ≤x≤ 0.75) has been prepared and characterised by powder X-ray and neutron diffraction, electrical and thermal transport property measurements, thermal analysis and SQUID magnetometry. With increasing cobalt content, the structure evolves from a disordered arrangement of cobalt ions in octahedral sites located in the van der Waals' gap (x≤ 0.2), through three different ordered vacancy phases, to a second disordered phase atx≥ 0.67. Powder neutron diffraction reveals that both octahedral and tetrahedral inter-layer sites are occupied in Co0.67TiS2. Charge transfer from the cobalt guest to the TiS2host affords a systematic tuning of the electrical and thermal transport properties. At low levels of cobalt intercalation (x< 0.1), the charge transfer increases the electrical conductivity sufficiently to offset the concomitant reduction in |S|. This, together with a reduction in the overall thermal conductivity leads to thermoelectric figures of merit that are 25% higher than that of TiS2,ZTreaching 0.30 at 573 K for CoxTiS2with 0.04 ≤x≤ 0.08. Whilst the electrical conductivity is further increased at higher cobalt contents, the reduction in |S| is more marked due to the higher charge carrier concentration. Furthermore both the charge carrier and lattice contributions to the thermal conductivity are increased in the electrically conductive ordered-vacancy phases, with the result that the thermoelectric performance is significantly degraded. These results illustrate the competition between the effects of charge transfer from guest to host and the disorder generated when cobalt cations are incorporated in the inter-layer space.
authors: Department of Chemistry , University of Reading , Whiteknights , Reading RG6 6AD , UK . Email: a.v.powell@reading.ac.uk.
authors: Gabin
authors: G
authors: Guélou
authors: Department of Chemistry , University of Reading , Whiteknights , Reading RG6 6AD , UK . Email: a.v.powell@reading.ac.uk.
authors: Paz
authors: P
authors: Vaqueiro
authors: Department of Chemistry , University of Reading , Whiteknights , Reading RG6 6AD , UK . Email: a.v.powell@reading.ac.uk.
authors: Jesús
authors: J
authors: Prado-Gonjal
authors: Laboratoire CRISMAT , UMR6508 CNRS ENSICAEN , 6 bd Marechal Juin , 14050 Caen Cedex 4 , France.
authors: Tristan
authors: T
authors: Barbier
authors: Laboratoire CRISMAT , UMR6508 CNRS ENSICAEN , 6 bd Marechal Juin , 14050 Caen Cedex 4 , France.
authors: Sylvie
authors: S
authors: Hébert
authors: Laboratoire CRISMAT , UMR6508 CNRS ENSICAEN , 6 bd Marechal Juin , 14050 Caen Cedex 4 , France.
authors: Emmanuel
authors: E
authors: Guilmeau
authors: STFC , Rutherford Appleton Laboratory , ISIS Facility , Didcot OX11 0QX , UK.
authors: Winfried
authors: W
authors: Kockelmann
authors: Department of Chemistry , University of Reading , Whiteknights , Reading RG6 6AD , UK . Email: a.v.powell@reading.ac.uk.
authors: Anthony V
authors: AV
authors: Powell