4 research outputs found
Defect Engineering for High-Performance n‑Type PbSe Thermoelectrics
Introducing
structural defects such as vacancies, nanoprecipitates,
and dislocations is a proven means of reducing lattice thermal conductivity.
However, these defects tend to be detrimental to carrier mobility.
Consequently, the overall effects for enhancing ZT are often compromised.
Indeed, developing strategies allowing for strong phonon scattering
and high carrier mobility at the same time is a prime task in thermoelectrics.
Here we present a high-performance thermoelectric system of Pb<sub>0.95</sub>(Sb<sub>0.033</sub>□<sub>0.017</sub>)Se<sub>1–<i>y</i></sub>Te<sub><i>y</i></sub> (□ = vacancy; <i>y</i> = 0–0.4) embedded with unique defect architecture.
Given the mean free paths of phonons and electrons, we rationally
integrate multiple defects that involve point defects, vacancy-driven
dense dislocations, and Te-induced nanoprecipitates with different
sizes and mass fluctuations. They collectively scatter thermal phonons
in a wide range of frequencies to give lattice thermal conductivity
of ∼0.4 W m<sup>–1</sup> K<sup>–1</sup>, which
approaches to the amorphous limit. Remarkably, Te alloying increases
a density of nanoprecipitates that affect mobility negligibly and
impede phonons significantly, and it also decreases a density of dislocations
that scatter both electrons and phonons heavily. As <i>y</i> is increased to 0.4, electron mobility is enhanced and lattice thermal
conductivity is decreased simultaneously. As a result, Pb<sub>0.95</sub>(Sb<sub>0.033</sub>□<sub>0.017</sub>)Se<sub>0.6</sub>Te<sub>0.4</sub> exhibits the highest ZT ∼ 1.5 at 823 K, which is
attributed to the markedly enhanced power factor and reduced lattice
thermal conductivity, in comparison with a ZT ∼ 0.9 for Pb<sub>0.95</sub>(Sb<sub>0.033</sub>□<sub>0.017</sub>)Se that contains
heavy dislocations only. These results highlight the potential of
defect engineering to modulate electrical and thermal transport properties
independently. We also reveal the defect formation mechanisms for
dislocations and nanoprecipitates embedded in Pb<sub>0.95</sub>(Sb<sub>0.033</sub>□<sub>0.017</sub>)Se<sub>0.6</sub>Te<sub>0.4</sub> by atomic resolution spherical aberration-corrected scanning transmission
electron microscopy
High-Power-Density Skutterudite-Based Thermoelectric Modules with Ultralow Contact Resistivity Using Fe–Ni Metallization Layers
Most reported thermoelectric modules
suffer from considerable power loss due to high electrical and thermal
resistivity arising at the interface between thermoelectric legs and
metallic contacts. Despite increasing complaints on this critical
problem, it has been scarcely tackled. Here we report the metallization
layer of Fe–Ni alloy seamlessly securing skutterudite materials
and metallic electrodes, allowing for a minimal loss of energy transferred
from the former. It is applied to an 8-couple thermoelectric module
that consists of n-type (Mm,Sm)<sub><i>y</i></sub>Co<sub>4</sub>Sb<sub>12</sub> (ZT<sub>max</sub> = 0.9) and p-type DD<sub><i>y</i></sub>Fe<sub>3</sub>CoSb<sub>12</sub> (ZT<sub>max</sub> = 0.7) skutterudite materials. It performs as a diffusion barrier
suppressing chemical reactions to produce a secondary phase at the
interface. Consequent high thermal stability of the module results
in the lowest reported electrical contact resistivity of 2.2–2.5
μΩ cm<sup>2</sup> and one of the highest thermoelectric
power density of 2.1 W cm<sup>–2</sup> for a temperature difference
of 570 K. Employing a scanning transmission electron microscope equipped
with an energy-dispersive X-ray spectroscope detector, we confirmed
that it is negligible for atomic diffusion across the interface and
resulting formation of a detrimental secondary phase to energy transfer
and thermal stability of the thermoelectric module
Extraordinary Off-Stoichiometric Bismuth Telluride for Enhanced n‑Type Thermoelectric Power Factor
Thermoelectrics
directly converts waste heat into electricity and
is considered a promising means of sustainable energy generation.
While most of the recent advances in the enhancement of the thermoelectric
figure of merit (<i>ZT</i>) resulted from a decrease in
lattice thermal conductivity by nanostructuring, there have been very
few attempts to enhance electrical transport properties, i.e., the
power factor. Here we use nanochemistry to stabilize bulk bismuth
telluride (Bi<sub>2</sub>Te<sub>3</sub>) that violates phase equilibrium,
namely, phase-pure n-type K<sub>0.06</sub>Bi<sub>2</sub>Te<sub>3.18</sub>. Incorporated potassium and tellurium in Bi<sub>2</sub>Te<sub>3</sub> far exceed their solubility limit, inducing simultaneous increase
in the electrical conductivity and the Seebeck coefficient along with
decrease in the thermal conductivity. Consequently, a high power factor
of ∼43 μW cm<sup>–1</sup> K<sup>–2</sup> and a high <i>ZT</i> > 1.1 at 323 K are achieved. Our
current synthetic method can be used to produce a new family of materials
with novel physical and chemical characteristics for various applications
Enhancing p‑Type 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 ∼1.2 at 773 K as well as average <i>ZT</i> of ∼0.5 from RT to 773 K is achieved for Na<sub>0.01</sub>(Sn<sub>1–<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>1–<i>x</i></sub>Pb<sub><i>x</i></sub>Se (0 < <i>x</i> ≤ 0.2; <i>y</i> = 0, 0.01) alloys spontaneously form nanoscale particles
with a typical size of ∼5–10 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