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Title: Nanoscale {alpha}-structural domains in the phonon-glass thermoelectric material {beta}-Zn{sub 4}Sb{sub 3}

Abstract

A study of the local atomic structure of the promising thermoelectric material {beta}-Zn{sub 4}Sb{sub 3}, using atomic pair distribution function (PDF) analysis of x-ray- and neutron-diffraction data, suggests that the material is nanostructured. The local structure of the {beta} phase closely resembles that of the low-temperature {alpha} phase. The {alpha} structure contains ordered zinc interstitial atoms which are not long range ordered in the {beta} phase. A rough estimate of the domain size from a visual inspection of the PDF is < or approx. 10 nm. It is probable that the nanoscale domains found in this study play an important role in the exceptionally low thermal conductivity of {beta}-Zn{sub 4}Sb{sub 3}.

Authors:
; ;  [1]; ;  [2]
  1. Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1116 (United States)
  2. Department of Materials Science, California Institute of Technology, Pasadena, California 91125 (United States)
Publication Date:
OSTI Identifier:
20957785
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 13; Other Information: DOI: 10.1103/PhysRevB.75.134103; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANTIMONY COMPOUNDS; DISTRIBUTION FUNCTIONS; GLASS; INTERSTITIALS; NANOSTRUCTURES; NEUTRON DIFFRACTION; PHONONS; TEMPERATURE RANGE 0065-0273 K; THERMAL CONDUCTIVITY; THERMOELECTRIC MATERIALS; THERMOELECTRICITY; X-RAY DIFFRACTION; ZINC; ZINC COMPOUNDS

Citation Formats

Kim, H. J., Bozin, E. S., Billinge, S. J. L., Haile, S. M., and Snyder, G. J. Nanoscale {alpha}-structural domains in the phonon-glass thermoelectric material {beta}-Zn{sub 4}Sb{sub 3}. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.134103.
Kim, H. J., Bozin, E. S., Billinge, S. J. L., Haile, S. M., & Snyder, G. J. Nanoscale {alpha}-structural domains in the phonon-glass thermoelectric material {beta}-Zn{sub 4}Sb{sub 3}. United States. doi:10.1103/PHYSREVB.75.134103.
Kim, H. J., Bozin, E. S., Billinge, S. J. L., Haile, S. M., and Snyder, G. J. Sun . "Nanoscale {alpha}-structural domains in the phonon-glass thermoelectric material {beta}-Zn{sub 4}Sb{sub 3}". United States. doi:10.1103/PHYSREVB.75.134103.
@article{osti_20957785,
title = {Nanoscale {alpha}-structural domains in the phonon-glass thermoelectric material {beta}-Zn{sub 4}Sb{sub 3}},
author = {Kim, H. J. and Bozin, E. S. and Billinge, S. J. L. and Haile, S. M. and Snyder, G. J.},
abstractNote = {A study of the local atomic structure of the promising thermoelectric material {beta}-Zn{sub 4}Sb{sub 3}, using atomic pair distribution function (PDF) analysis of x-ray- and neutron-diffraction data, suggests that the material is nanostructured. The local structure of the {beta} phase closely resembles that of the low-temperature {alpha} phase. The {alpha} structure contains ordered zinc interstitial atoms which are not long range ordered in the {beta} phase. A rough estimate of the domain size from a visual inspection of the PDF is < or approx. 10 nm. It is probable that the nanoscale domains found in this study play an important role in the exceptionally low thermal conductivity of {beta}-Zn{sub 4}Sb{sub 3}.},
doi = {10.1103/PHYSREVB.75.134103},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 13,
volume = 75,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}
  • The low-temperature structural phase transitions of Bi, Pb, In and Sn-doped samples of thermoelectric Zn{sub 4}Sb{sub 3} have been characterized on crystals grown from molten metal fluxes, using electrical resistance and single crystal X-ray diffraction measurements. Room temperature stable, disordered, {beta}-Zn{sub 4}Sb{sub 3} undergoes two phase transitions at 254 and 235 K to the consecutively higher ordered phases {alpha} and {alpha}', respectively. The ideal crystallographic composition of {alpha}-Zn{sub 4}Sb{sub 3} is Zn{sub 13}Sb{sub 10}. The {alpha}-{alpha}' transformation is triggered by a slight and homogenous Zn deficiency with respect to this composition and introduces a compositional modulation in the {alpha}-Zn{sub 4}Sb{submore » 3} structure. When preparing {beta}-Zn{sub 4}Sb{sub 3} in the presence of metals with low melting points (Bi, Sn, In, Pb) the additional metal atoms are unavoidably incorporated in small concentrations (0.04-1.3 at%) and act as dopants. This incorporation alters the subtle balance between Zn disorder and Zn deficiency in Zn{sub 4}Sb{sub 3} and has dramatic consequences for its low-temperature structural behavior. From molten metal flux synthesis it is possible to obtain (doped) Zn{sub 4}Sb{sub 3} samples which (1) only display a {beta}-{alpha} transition, (2) only display a {beta}-{alpha}' transition, or (3) do not display any low-temperature phase transition at all. Case (2) provided diffraction data with a sufficient quality to obtain a structural model for highly complex, compositionally modulated, {alpha}'-Zn{sub 4}Sb{sub 3}. The crystallographic composition of this phase is Zn{sub 84}Sb{sub 65}. - Graphical abstract: The thermoelectric material Zn{sub 4}Sb{sub 3} displays complex temperature polymorphism. Room temperature stable, disordered, {beta}-Zn{sub 4}Sb{sub 3} undergoes two phase transitions at 254 and 235 K to the consecutively higher ordered phases {alpha} and {alpha}', respectively. The {alpha}-{alpha}' transformation is triggered by a slight and homogenous Zn deficiency and introduces a compositional modulation in the {alpha}-Zn{sub 4}Sb{sub 3} structure.« less
  • The phase homogeneity of spark plasma sintered thermoelectric Zn{sub 4}Sb{sub 3} pellets along the pressing direction has been studied by potential Seebeck microprobe scanning and spatially resolved x-ray diffraction. Significant variations in the Seebeck coefficient reflect presence of different crystalline phases. The emergence of the ZnSb phase at the bottom of the pellet and metallic Zn impurity at the top explains the variation in the Seebeck coefficients. Quantitative phase distributions along the pressing axis were determined from the Rietveld refinements of spatially resolved x-ray diffraction patterns. These reveal a migration of highly mobilized Zn atoms under the direct current appliedmore » during spark plasma sintering.« less
  • The influence of Zn vacancy on lattice thermal conductivity of {beta}-Zn{sub 4}Sb{sub 3} is studied by non-equilibrium molecular dynamics approach. The lattice thermal conductivity of single-crystal bulk {beta}-Zn{sub 4}Sb{sub 3} decreases rapidly when there is Zn vacancy, and then when the vacancy grows, the lattice thermal conductivity decreases further but rather slowly, which suggests a scaling law of k{sub v}{approx}n{sub v}{sup -{alpha}} of Zn atom vacancy (n{sub v}) to lattice thermal conductivity (k{sub vac}). This phenomenon is attributed to the fact that the existence of vacancy scattering can significantly decrease the mean free path. When the Zn atom vacant proportionmore » reaches 10%, that is the vacancy model of {beta}-Zn{sub 4}Sb{sub 3}, the lattice thermal conductivity is 1.32 W/mk along the x-axis and 1.62 W/mk along the z-axis, respectively, which drops by {approx}90% that of its full occupancy model. Therefore, our calculations show that the 10% Zn atom vacancy in {beta}-Zn{sub 4}Sb{sub 3} is the main reason for its exceptionally low thermal conductivity, and the interstitial Zn atoms have little effect on the thermal conductivity of single-crystal {beta}-Zn{sub 4}Sb{sub 3}. - Graphical abstract: The bulk thermal conductivity (k{sub pure}) is 11.88 W/mk along the x-axis and 20.00 W/mk the z-axis. When it is 10% vacancy, namely the vacancy model of {beta}-Zn{sub 4}Sb{sub 3}, the thermal conductivity of {beta}-Zn{sub 4}Sb{sub 3} is 1.32 W/mk along the x-axis and 1.62 W/mk along the z-axis, respectively, which reduces by {approx}90% that of its full occupancy model. Our calculations show that the 10% Zn atom vacancy in the crystal structure of {beta}-Zn{sub 4}Sb{sub 3} is the main reason for its exceptionally low thermal conductivity, and the interstitial Zn atoms have little effect on the thermal conductivity of single-crystal {beta}-Zn{sub 4}Sb{sub 3}. Highlights: Black-Right-Pointing-Pointer The lattice stability of {beta}-Zn{sub 4}Sb{sub 3} decreases remarkably with the growing vacancy. Black-Right-Pointing-Pointer 10% Zn vacancy leads to its low thermal conductivity and structural instability. Black-Right-Pointing-Pointer Interstitial Zn atoms in {beta}-Zn{sub 4}Sb{sub 3} mainly stabilize the crystal structure.« less
  • Single-phase Zn{sub 4}Sb{sub 3} and ZnSb-containing samples were prepared by Plasma Activated Sintering. An abrupt decrease of thermal conductivity was found at about 400 K, which is attributed to the microstructure change of Zn{sub 4}Sb{sub 3}. Nanoscale inclusions and compositional inhomogeneities were found in Zn{sub 4}Sb{sub 3} sample at 473 K by high-resolution transmission electron microscopy. The phonon scattering is enhanced by increasing grain boundaries and chaotic structure, which reduces the thermal conductivity and increases the thermoelectric performance of Zn{sub 4}Sb{sub 3} at elevated temperature. The Rietveld refinement results show that large ZnSb grains in ZnSb-containing samples will accommodate excessmore » Zn atoms, and then reduce thermoelectric performance.« less
  • We demonstrate the control of phase composition in Bridgman-grown β-Zn{sub 4}Sb{sub 3} crystals by indium doping, an effective way to overcome the difficulty of growing very pure β-Zn{sub 4}Sb{sub 3} thermoelectric material. The crystal structures are characterized by Rietveld refinement with synchrotron X-ray diffraction data. The results show an anisotropic lattice expansion in In-doped β-Zn{sub 4}Sb{sub 3} wherein the zinc atoms are partially substituted by indium ones at 36f site of R-3c symmetry. Through the elimination of ZnSb phase, all the three individual thermoelectric properties are simultaneously improved, i.e., increasing electrical conductivity and Seebeck coefficient while reducing thermal conductivity. Undermore » an optimal In concentration (x = 0.05), pure phase β-Zn{sub 4}Sb{sub 3} crystal can be obtained, which possesses a high figure of merit (ZT) of 1.4 at 700 K.« less