Abstract
A variety of crystals contain quasi-one-dimensional substructures, which yield distinctive electronic, spintronic, optical and thermoelectric properties. There is a lack of understanding of the lattice dynamics that influences the properties of such complex crystals. Here we employ inelastic neutron scatting measurements and density functional theory calculations to show that numerous low-energy optical vibrational modes exist in higher manganese silicides, an example of such crystals. These optical modes, including unusually low-frequency twisting motions of the Si ladders inside the Mn chimneys, provide a large phase space for scattering acoustic phonons. A hybrid phonon and diffuson model is proposed to explain the low and anisotropic thermal conductivity of higher manganese silicides and to evaluate nanostructuring as an approach to further suppress the thermal conductivity and enhance the thermoelectric energy conversion efficiency. This discovery offers new insights into the structure-property relationships of a broad class of materials with quasi-one-dimensional substructures for various applications.
| Original language | English |
|---|---|
| Article number | 6723 |
| Journal | Nature Communications |
| Volume | 6 |
| DOIs | |
| State | Published - Apr 15 2015 |
Funding
The work is primarily supported by the US National Science Foundation (NSF), Department of Energy (DOE) Joint Thermoelectric Partnership (NSF award numbers: CBET-1048767 and CBET-1048625). A.W. is supported by a NSF Graduate Research Fellowship. O.D. acknowledges support by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, through the Office of Science Early Career Research Program. J.Y. was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. Part of the research conducted at Oak Ridge National Laboratory’s Spallation Neutron Source (SNS) and High Flux Isotope Reactor (HFIR) was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. S.N.G. gratefully acknowledges support from the NSF SEES Postdoctoral Fellowship (NSF award number EEC-1313968). D.A.S. acknowledges support from the National Science Foundation under Grant No. CBET-1066406. J.C. and N.M. acknowledge support from project Carnot SIEVE. A portion of the simulations for this work were performed on the Intel Cluster at the Cornell Nanoscale Facility, part of the National Nanotechnology Infrastructure Network (NNIN) funded by NSF. Additional simulations were made possible through Texas Advanced Computing Center (TACC) at The University of Texas at Austin and Research Services at Boston College. D.P.S. acknowledges support from the NSERC Postdoctoral Fellowship. The far infrared measurements were carried out with the help of Dr Mikhail Belkin and Feng Lu at the University of Texas at Austin. L.S. thanks David Broido for pointing out anisotropic phonon life time in Si and PbTe, and Ray Orbach for sharing insights on vibrational hoping in disordered systems.
| Funders | Funder number |
|---|---|
| High Flux Isotope Reactor | |
| Office of Basic Energy Sciences | |
| Scientific User Facilities Division | |
| US Department of Energy | EEC-1313968 |
| US National Science Foundation | |
| National Science Foundation | 1048767, 1313968, 1066406 |
| U.S. Department of Energy | CBET-1048767, CBET-1048625 |
| Office of Science | |
| Basic Energy Sciences | |
| Division of Materials Sciences and Engineering | |
| Natural Sciences and Engineering Research Council of Canada |