a1 Department of Physics, University of Virginia, Charlottesville, Virginia 22904-4714
a2 Department of Physics & Astronomy, Clemson University, Clemson, South Carolina 29634
a3 Center for Solid State Energetics, RTI International, Research Triangle Park, North Carolina 27709
Half-Heusler (HH) phases, a versatile class of alloys with promising functional properties, have recently gained attention as emerging thermoelectric materials. These materials are investigated from the perspective of thermal and electronic transport properties for enhancing the dimensionless figure of merit (ZT) at 800–1000 K. The electronic origin of thermopower enhancement is reviewed. Grain refinement and embedment of nanoparticles in HH alloy hosts were used to produce fine-grained as well as nanocomposites and monolithic nanostructured materials. Present experiments indicated that n-type Hf0.6Zr0.4NiSn0.995Sb0.005 HH alloys and p-type Hf0.3Zr0.7CoSn0.3Sb0.7/nano-ZrO2 composites can attain ZT = 1.05 and 0.8 near 900–1000 K, respectively. The observed ZT enhancements could be attributed to multiple origins; in particular, the electronic origin was identified. The prospect for higher ZT was investigated in light of a recently developed nanostructure model of lattice thermal conductivity. Tests performed on p–n couple devices from the newly developed HH materials showed good power generation efficiencies—achieving 8.7% efficiency for hot-side temperatures of about 700 °C.
(Received August 02 2011)
(Accepted September 20 2011)
b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs.org/jmr-editor-manuscripts/.
This paper has been selected as an Invited Feature Paper.