Google Search

A2: Medium temperature materials

Oxides and sulfides:  is there an impact of magnetism on the thermoelectric properties?

A. Maignan*, E. Guilmeau, D. Berthebaud, F. Gascoin, R. Daou and S. Hébert 
Laboratoire CRISMAT, UMR 6508 CNRS ENSICAEN - 6 Bd du Maréchal Juin - 14050 CAEN FRANCE

In the recent years, the strongly correlated systems have attracted much attention for thermoelectricity (TE). Magnetic transition metals in p-type oxides are responsible for unexpected large Seebeck (S) values together with quasi T-independent over broad T ranges. A comparison between layered cobaltites and perovskite ruthenates emphasizes the role of the spins on both S and electrical resistivity (ρ). Nonetheless, according to their ionocovalent character, the power factor of these oxides (PF=S2/ρ) remains too small for applications in TE (at 300K, »0.1mW.K-2.m-1). In that respect, sulfides are more covalent and larger PF values (300K, »1mW.K-2.m-1) were evidenced in the CoS2 itinerant ferromagnet [2]. But the rather 3D structural type of this pyrite and others such as Cr2S3 and Cr5S6 [3] is responsible for their too high thermal conductivity (κ300K remains too high ~ 10W.K-1.m-1).

Consequently, CdI2 derived structures have been revisited. They offer several possibilities to control the doping level and engineer the lattice part of κ, as for TiS2 with the series of SPS ceramics or crystals with intercalated species, M=Cu or Co in MxTiS2 [4, 5], with cation or anion substitutions as for Ti1-xTaxS2 [6] or TiS2-xSex [7], respectively. Strong κlatt reductions were demonstrated by comparing CoxTiS2 crystals, with Co cation intercalation, and (CoS2)xTiS2 composite crystals, with CoS2 dots [5] even if for the latter, the presence of ferromagnetic CoS2 does not impact the TE properties. On the other hand, for AgCrS2 and AgCrSe2 with (Cr3+, S=3/2), a clear link is found between S, κ and the antiferromagnetism [8]. Considering these results, several routes will be proposed to take benefit of magnetism for TE properties enhancement.

References:

[1] For a review, S. Hébert, W. Kobayashi, H. Muguerra, Y. Bréard, N. Ragavendra, F. Gascoin, E. Guilmeau and A. Maignan, Phys. Status Solidi A 210 (2013) 69.

[2]  S. Hébert, E. Guilmeau, D. Berthebaud, O.I. Lebedev, V. Roddatis and A. Maignan,
J. of Appl. Phys. 114 (2013) 103703.

[3]  A. Maignan,  E. Guilmeau, F. Gascoin, Y. Bréard and V. Hardy, Sci. Technol. Adv. Mater 13 (2012) 053003.

[4]  E. Guilmeau, Y. Bréard and A. Maignan, Appl. Phys. Lett. 99 (2011) 052107.

[5]  R. Daou, H. Takahashi, S. Hébert, M. Beaumale, E. Guilmeau and A. Maignan (submitted).

[6]  M. Beaumale, T. Barbier, Y. Bréard, S. Hébert, Y. Kinemuchi and E. Guilmeau,
J. of Appl. Phys. 115 (2014) 043704.

[7]  F. Gascoin, N. Raghavendra, E. Guilmeau and Y. Bréard, J. Alloys. Compd. 521 (2012) 21.

[8]   To be published.