Thermoelectric performance of nanostructured p-type Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb_1–xSn_xhalf-Heusler alloys

Journal Article · Sat Jun 01 00:00:00 EDT 2013 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2013.03.024· OSTI ID:22306316

Maji, Pramathesh; Makongo, Julien P.A. ^[1]; Zhou, Xiaoyuan; Chi, Hang; Uher, Ctirad ^[2]

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1. Laboratory for Emerging Energy and Electronic Materials, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109 (United States)
2. Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States)

Several compositions of the p-type half-Heusler alloys Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb_1–xSn_x (0≤x≤0.4) were synthesized by mechanically alloying high purity elemental powders using hardened steel jars and balls on a high energy shaker mill. Powder X-ray diffraction (XRD) investigations of several aliquots taken after regularly spaced milling time suggested that single phase products with half-Heusler (HH) structure can be obtained after 10 h. However, XRD and transmission electron microscopy (TEM) studies of several specimens obtained from compacted polycrystalline powders of Z₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb_1–xSn_x alloys using a uniaxial hot press (HP) revealed the presence of CoSb inclusions with various sizes embedded inside the HH matrix. Hall effect, electrical conductivity, and thermopower data collected between 300 K and 775 K on several compositions suggested that electronic transport in the synthesized Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb_1–xSn_x/CoSb composites strongly depends on the average size and/or mole fraction of the embedded CoSb inclusions rather than the fraction (x) of Sn substituting for Sb. Among the samples investigated, the nanocomposite with x=0.2, which contains nanometer-scale CoSb inclusions, showed the largest power factor (800 μW/K² m at 775 K) and the lowest lattice thermal conductivity (~2.2 W/m K at 775 K) leading to a six-fold enhancement in the figure of merit when compared to the Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb₀.₉₉Sn₀.₀₁ bulk matrix. - Graphical abstract: CoSb nanoinclusions embedded into a p-type Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb_1–xSn_x half-Heusler matrix simultaneously boost the thermopower and carrier mobility leading to a drastic enhancement of the power factor of the resulting bulk nanostructured materials. Highlights: • The phase composition of half-Heusler (HH) alloy is very sensitive to the synthesis method. • Mechanical alloying (MA) of elements results in bulk HH matrix with CoSb inclusions. • CoSb nanoinclusions simultaneously boost the thermopower and carrier mobility with the HH matrix. • The MA process reduces lattice thermal conductivity due to high density of grain boundaries.

• OSTI ID: 22306316
• Journal Information: Journal of Solid State Chemistry, Vol. 202; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
77 NANOSCIENCE AND NANOTECHNOLOGY
CARRIER MOBILITY
DENSITY
ELECTRIC CONDUCTIVITY
GRAIN BOUNDARIES
HALL EFFECT
HEUSLER ALLOYS
INCLUSIONS
NANOSTRUCTURES
POLYCRYSTALS
POWDERS
STEELS
SYNTHESIS
THERMAL CONDUCTIVITY
THERMOELECTRIC PROPERTIES
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION