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2012 ; 13
(5
): 053003
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Revisiting some chalcogenides for thermoelectricity
#MMPMID27877513
Maignan A
; Guilmeau E
; Gascoin F
; Bréard Y
; Hardy V
Sci Technol Adv Mater
2012[Oct]; 13
(5
): 053003
PMID27877513
show ga
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(-4) W m(-1) K(-2)) to yield a satisfactory figure of merit zT. Changing the
anions from O(2-) to S(2-) and then to Se(2-) is a way to increase the covalency.
In this review, some examples of sulfides (binary Cr-S or derived from layered
TiS(2)) and an example of selenides, AgCrSe(2), 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 AgCrSe(2)
selenide 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 TiS(2) and Cu(0.1)TiS(2) are higher, reaching ?10(-3) W m(-1) K(-2).
Apparently the magnetism related to the Cr-S network is detrimental for the PF
when compared to the d(0) character of the Ti(4+) based sulfides. Finally, the
very low PF in AgCrSe(2) (PF = 2.25 × 10(-4) W m(1) K(-2) at 700 K) is
compensated by a very low thermal conductivity (? = 0.2 W m(-1) K(-1) from the
measured C(p)) leading to the highest zT value among the reviewed compounds
(zT(700K) = 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.