10-01 :: January 2010
nanotimes
33
News in Brief
Thermoelectrics //
Mismatched Alloys Are a Good Match
C
omputations performed on “Franklin,” a Cray
XT4 massively parallel processing system ope-
rated by the National Energy Research Scientific
Computing Center (NERSC), showed that the intro-
duction of oxygen impurities into a unique class of
semiconductors known as highly mismatched alloys
(HMAs) can substantially enhance the thermoelec-
Image: Contour plots showing electronic density of states
tric performance of materials without the customa-
in HMAs created from zinc selenide by the addition of (a)
ry degradation in electric conductivity
3.125-percent oxygen atoms, and (b) 6.25 percent oxy-
gen. The zinc and selenium atoms are shown in light blue
“We are predicting a range of inexpensive, abun-
and orange. Oxygen atoms (dark blue) are surrounded by
dant, non-toxic materials in which the band structure
high electronic density regions.© Junqiao Wu / LBL
can be widely tuned for maximal thermoelectric
efficiency,” says Junqiao Wu, a physicist with Berke-
ley Lab’s Materials Sciences Division and a professor
with UC Berkeley’s Department of Materials Sci- this conundrum, Wu and his colleagues turned to
ence and Engineering who led this research. “Speci- HMAs, an unusual new class of materials whose
fically, we’ve shown that the hybridization of elec- development has been led by another physicist with
tronic wave functions of alloy constituents in HMAs Berkeley Lab’s Materials Sciences Division, Wlady-
makes it possible to enhance thermopower without slaw Walukiewicz.
much reduction of electric conductivity, which is not
the case for conventional thermoelectric materials,” Joo-Hyoung Lee, Junqiao Wu, Jeffrey C. Grossman: Enhan-
he says. “Good thermoelectric materials should have cing the Thermoelectric Power Factor with Highly Mismat-
high thermopower, high electric conductivity, and ched Isoelectronic Doping, In: Physical Review Letters, Vol.
low thermal conductivity,” says Wu. “Enhancement 104(2010), Article 016602 (2010), DOI:10.1103/PhysRev-
in thermoelectric performance can be achieved by Lett.104.016602:
reducing thermal conductivity through nanostructu-

http://dx.doi.org/10.1103/PhysRevLett.104.016602
ring. However, increasing performance by increasing
thermopower has proven difficult because an incre-

http://www.mse.berkeley.edu/~jwu/
ase in thermopower has typically come at the cost of
a decrease in electric conductivity.” To get around