1 research outputs found
Enhancing pโType Thermoelectric Performances of Polycrystalline SnSe via Tuning Phase Transition Temperature
SnSe
emerges as a new class of thermoelectric materials since the
recent discovery of an ultrahigh thermoelectric figure of merit in
its single crystals. Achieving such performance in the polycrystalline
counterpart is still challenging and requires fundamental understandings
of its electrical and thermal transport properties as well as structural
chemistry. Here we demonstrate a new strategy of improving conversion
efficiency of bulk polycrystalline SnSe thermoelectrics. We show that
PbSe alloying decreases the transition temperature between <i>Pnma</i> and <i>Cmcm</i> phases and thereby can serve
as a means of controlling its onset temperature. Along with 1% Na
doping, delicate control of the alloying fraction markedly enhances
electrical conductivity by earlier initiation of bipolar conduction
while reducing lattice thermal conductivity by alloy and point defect
scattering simultaneously. As a result, a remarkably high peak <i>ZT</i> of โผ1.2 at 773 K as well as average <i>ZT</i> of โผ0.5 from RT to 773 K is achieved for Na<sub>0.01</sub>(Sn<sub>1โ<i>x</i></sub>Pb<sub><i>x</i></sub>)<sub>0.99</sub>Se. Surprisingly, spherical-aberration corrected
scanning transmission electron microscopic studies reveal that Na<sub><i>y</i></sub>Sn<sub>1โ<i>x</i></sub>Pb<sub><i>x</i></sub>Se (0 < <i>x</i> โค 0.2; <i>y</i> = 0, 0.01) alloys spontaneously form nanoscale particles
with a typical size of โผ5โ10 nm embedded inside the
bulk matrix, rather than solid solutions as previously believed. This
unexpected feature results in further reduction in their lattice thermal
conductivity