title: Revisiting some chalcogenides for thermoelectricity.
abstract: Thermoelectric materials that are efficient well above ambient temperature are needed to convert waste-heat into electricity. Many thermoelectric oxides were investigated for this purpose, but their power factor (PF) values were too small (∼10-4W m-1K-2) to yield a satisfactory figure of meritzT. Changing the anions from O2-to S2-and then to Se2-is a way to increase the covalency. In this review, some examples of sulfides (binary Cr-S or derived from layered TiS2) and an example of selenides, AgCrSe2, have been selected to illustrate the characteristic features of their physical properties. The comparison of the only two semiconducting binary chromium sulfides and of a layered AgCrSe2selenide shows that the PF values are also in the same order of magnitude as those of transition metal oxides. In contrast, the PF values of the layered sulfides TiS2and Cu0.1TiS2are higher, reaching ∼10-3W m-1K-2. Apparently the magnetism related to the Cr-S network is detrimental for the PF when compared to the d0character of the Ti4+based sulfides. Finally, the very low PF in AgCrSe2(PF = 2.25 × 10-4W m1K-2at 700 K) is compensated by a very low thermal conductivity (κ= 0.2 W m-1K-1from the measured Cp) leading to the highestzTvalue among the reviewed compounds (zT700K= 0.8). The existence of a glassy-like state for the Ag+cations above 475 K is believed to be responsible for this result. This result demonstrates that the phonon engineering in open frameworks is a very interesting way to generate efficient thermoelectric materials.
authors.affiliation: Laboratoire CRISMAT, UMR 6508 CNRS/ENSICAEN, 6 bd du Maréchal Juin F-14050 CAEN Cedex 4, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Maignan
authors.affiliation: Laboratoire CRISMAT, UMR 6508 CNRS/ENSICAEN, 6 bd du Maréchal Juin F-14050 CAEN Cedex 4, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Guilmeau
authors.affiliation: Laboratoire CRISMAT, UMR 6508 CNRS/ENSICAEN, 6 bd du Maréchal Juin F-14050 CAEN Cedex 4, France.
authors.forename: Franck
authors.initials: F
authors.lastname: Gascoin
authors.affiliation: Laboratoire CRISMAT, UMR 6508 CNRS/ENSICAEN, 6 bd du Maréchal Juin F-14050 CAEN Cedex 4, France.
authors.forename: Yohann
authors.initials: Y
authors.lastname: Bréard
authors.affiliation: Laboratoire CRISMAT, UMR 6508 CNRS/ENSICAEN, 6 bd du Maréchal Juin F-14050 CAEN Cedex 4, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Hardy
keywords: chromium selenide; chromium sulfide; thermoelectricity; titanium sulfide