Multi-phase Nanocrystalline Thermoelectric Materials
In a multi component nanocrystalline material, crystallites and interfacial
nanostructures form a disordered morphology. In such a disordered nanostructured
material, the energy disruption for both electrons and phonons can happen in a
time scale that is smaller or comparable to the energy relaxation time.
Therefore, the charge and heat carriers can maintain an energetically
non-equilibrium distribution that can result in fundamentally different
electrical and thermal properties than in the crystalline materials.
The concept of multi-phase nanocrystalline (or nanocomposite) bulk alloys
represents a radical alternative to conventional homogeneous bulk materials.
Nanocomposites are considered new materials different from their parent
materials. Although they consist of similar atomic structures as the constituent
elements, using size as a parameter effectively provides “new” materials in
terms of their physical properties. The ability to tune the property of the
multi-phase nanocrystalline material by controlling the material composition,
crystallite sizes and distribution as well as manipulating the interface
potential barrier height by alloying without deteriorating the nanocrystalline
quality offers extra degrees of freedom for creating material structures with
novel electrical properties.
Such new characteristics offer a landscape for discovering new material systems
for engineering applications. For instance, maintaining the energy of hot
electrons has been a long standing challenge in low band-gap photovoltaics (PV).
A low band-gap PV material can harvest a larger part of the solar spectra;
however, the electrons excited by high energy photons relax to the band edge
giving up their extra energy to phonons. Therefore, the extra energy is wasted
as heat.
A similar motivation exists for enhancing the power factor in thermoelectric
materials. Instead of focusing on semiconducting materials with a highly
asymmetric density of states close to the Fermi level to increase the average
energy of charge carriers (hence the Seebeck coefficient), the multi-phase
nanocrystalline approach can offer a new way via the non-equilibrium transport
of charge carriers.
This method alleviates the fundamental trade-off between the electrical
conductivity and the Seebeck coefficient. The high electron density in the metal
(>1022/cm-3) compensates for the negligible contribution
to the conductivity from the majority of the electrons in the metal that have
energies below the top of the interface potential barrier.
Achievements
Over the last several years we
have grown and tested over a thousand of nanostructured thermoelectric material
samples. These materials often with different morphologies or alloy composition
ratios have been characterized and provided us with valuable information. For
examples, in order to enhance the TE properties of β-FeSi2, we
developed nanocomposite of FeSi2 with SiGe in different composition
ratios. Our materials have shown two fold enhancement in ZT of this material
structure. For high temperature applications, we focused on several materials
including higher manganese silicide (HMS), and SiGe. We also performed an
extensive research on nanocomposite of Mg2Si-SiGe, which showed
promising ZT enhancement. On another direction we worked on finding optimum
electrical contact to HMS. We investigated several materials including Co, Ni,
Cr, Ti, Mo, MnSi, MoSi2, and TiSi2 in search of the best
contact material to HMS.
Our experimental data has shown that the nanocomposite of these metal silicides
and SiGe can significantly enhance the thermoelectric power factor of SiGe by
enhancing the Seebeck coefficient and/or reducing the thermal conductivity.
Figure 1
plots the ZT of some of our recent samples showing the enhancement of
figure-of-merit in both the p-type and n-type materials. Nanocomposite of (Bi,Sb)2Te3,
α-FeSi2/SiGe, Mg2Si/SiGe, and nanocrystalline (NC) SiGe
compared with that of RTG SiGe used in NASA space crafts are shown. The data
shows that in all nanocomposite samples ZT is enhanced.
We have also observed
a significant improvement in ZT of p-type SiGe nanocomposite materials
accounting for ~80% improvement in SiGe compared to its single crystalline bulk
structures. For close to room temperature applications, we also worked on
nanocomposite of BiTe-SbTe and achieved the highest reported ZT of this material
structure (ZT=1.6). This research was funded by Air Force Office of Scientific
Research and National Science Foundation.
Selected Representative Publications
1.
Enhancement of thermoelectric power factor of silicon germanium films grown by
electrophoresis deposition,
Amin Nozariasbmarza, Armin Tahmasbi Rad, Zahra Zamanipourb, Jerzy S. Krasinskib,
Lobat Tayebia, Daryoosh Vashaee, Scripta Materialia, ISSN 1359-6462,
http://dx.doi.org/10.1016/j.scriptamat.2013.06.025 (2013).
2.
The effect of phase heterogeneity on thermoelectric properties of nanostructured
silicon germanium alloy,
Zahra Zamanipour, Payam Norouzzadeh, Jerzy S. Krasinski, Lobat Tayebi, Daryoosh
Vashaee, J. Appl. Phys. 114, 023705 (2013); http://dx.doi.org/10.1063/1.4813474.
3.
Comparison of boron precipitation in p-type bulk nanostructured and
polycrystalline silicon germanium alloy,
Zahra Zamanipour, Jerzy S. Krasinski, and Daryoosh Vashaee, J. Appl. Phys. 113,
143715 (2013); doi: 10.1063/1.4801388
4.
The effect of synthesis parameters on transport properties of nanostructured
bulk thermoelectric p-type silicon germanium alloy,
Zahra Zamanipour, Xinghua Shi, Arash M. Dehkordi, Jerzy S. Krasinski, Daryoosh
Vashaee, Physica Status Solidi (b), DOI: 10.1002/pssa.201228102 (2012)
5.
An investigation of electrical contacts for higher manganese silicide,
Xinghua She, Zahra Zamanipour, Jerzy S. Krasinski, Alan Tree and Daryoosh
Vashaee, Journal of Electronic Materials, Volume 41, Number 9 (2012), 2331-2337
6.
Enhancement in thermoelectric power factor of polycrystalline Bi0.5Sb1.5Te3
by crystallite alignment,
Arash Mehdizadeh Dehkordi, Daryoosh Vashaee, Physica Status Solidi (a), DOI:
10.1002/pssa.201228147 (2012)
7.
Comparison of thermoelectric properties of p-type nanostructured bulk Si0.8Ge0.2
alloy with Si0.8Ge0.2 composites embedded with CrSi2
nano-inclusisons,
Zahra Zamanipour and Daryoosh Vashaee, J. Appl. Phys. 112,
093714 (2012) http://dx.doi.org/10.1063/1.4764919
8.
Synthesis, characterization, and thermoelectric properties of nanostructured
bulk p-type MnSi1.73, MnSi1.75, and MnSi1.77,
Z. Zamanipour, X. Shi, M. Mozafari , J. S. Krasinski, L. Tayebi, D.
Vashaee, Ceramics International, (In press-2012 Available online 5 September
2012, ISSN 0272-8842, 10.1016/j.ceramint.2012.08.086. )
9.
The effect of nanostructuring on thermoelectric transport properties of p-type
higher manganese silicide MnSi1.73,
Payam Norouzzadeh, Zahra Zamanipour, Jerzy Krasinski, Daryoosh Vashaee, J. of
Applied Physics, 112, 124308 (2012); doi: 10.1063/1.4769884
10.
Increased Phonon Scattering by Nanograins and Point Defects in Nanostructured
Silicon with a Low Concentration of Germanium,
Chen, G. , Zhu, G.H. , Lee, H. , Lan, Y.C. , Wang, X.W. , Joshi, G. , Wang,
D.Z., Yang, J., Vashaee, D., Guilbert, H., Pillitteri, A., Dresselhaus, M.S.,
Ren, Z.F., Physical Review Letters, Volume 102, Issue 19, 14 May 2009, Article
number 196803
11.
High Thermoelectric Performance of Nanostructured Bismuth Antimony Telluride
Bulk Alloys,
Bed Poudel, Qing Hao, Yi Ma, Yucheng Lan, Xiao Yan, Dezhi Wang, D. Vashaee, M.
Dresselhaus, Gang Chen, and Z. F. Ren, , Science Express Research Articles, 20
March 2008, 10.1126/science.1156446.
12.
Thermionic Power Generation at High Temperatures Using SiGe/Si Superlattices,
Daryoosh Vashaee, Ali Shakouri, J. Appl. Phys. 101, 053719 (2007).
13.
Enhancement of Thermoelectric Power Factor in SiGe-CrSi2 Composite
Alloy,
Zahra Zamanipour, Daryoosh Vashaee, IEEE Green Technologies Conference 2012 -
Energy Generation & Storage Technologies, Tulsa, Oklahoma, April 19-20, 2012
14.
Economical FeSi2-SiGe Composites for Thermoelectric Power Generation,
Yin Liu, Daryoosh Vashaee, IEEE Green Technologies Conference 2012 - Energy
Generation & Storage Technologies, Tulsa, Oklahoma, April 19-20, 2012
15.
Thermal and Thermoelectric Properties of Nanostructured Versus Crystalline SiGe,
Lobat Tayebi, Zahra Zamanipour, Masoud Mozafari, Payam Norouzzadeh, Jerzy S.
Krasinski, Kenneth F. Ede, Daryoosh Vashaee, IEEE Green Technologies Conference
2012 - Energy Generation & Storage Technologies, Tulsa, Oklahoma, April 19-20,
2012
16.
Thermoelectric Properties of Mg2Si Doped with Bi and Al with
Conductive Glass Inclusion,
Nikhil Satyala, Jerzy S. Krasinski, Daryoosh Vashaee, IEEE Green Technologies
Conference 2012 - Energy Generation & Storage Technologies, Tulsa, Oklahoma,
April 19-20, 2012
17.
A Method to Measure the Thermal Conductivity of Thermoelectric Nanowires,
Nahida Akhter, Daryoosh Vashaee, IEEE Green Technologies Conference 2012 -
Energy Generation & Storage Technologies, Tulsa, Oklahoma, April 19-20, 2012
18.
Enhancement of Thermoelectric Efficiency of MnSi1.75 with the
Addition of Externally Processed Nanostructured MnSi,
Xinghua Shi, Zahra Zamanipour, Kenneth F. Ede, Jerzy S. Krasinski, Daryoosh
Vashaee, IEEE Green Technologies Conference 2012 - Energy Generation & Storage
Technologies, Tulsa, Oklahoma, April 19-20, 2012
19.
Cost Effective Synthesis of Bulk Thermoelectric Higher Manganese Silicide for
Waste Heat Recovery and Environmental Protection,
Xinghua Shi, Zahra Zamanipour, Kenneth F. Ede, Jerzy S. Krasinski, Daryoosh
Vashaee, IEEE Green Technologies Conference 2012 - Energy Generation & Storage
Technologies, Tulsa, Oklahoma, April 19-20, 2012
20.
Anomalous Thermoelectric Behavior of BiSeTe Doped with SiGe:As,
Oonnittan Jacob Panachaveettil, Ranji Vaidyanathan, Jerzy S. Krasinski, Daryoosh
Vashaee, IEEE Green Technologies Conference 2012 - Energy Generation & Storage
Technologies, Tulsa, Oklahoma, April 19-20, 2012
21.
Differential Thermal Analysis of Nanostructured Si0.8Ge0.2
Thermoelectric Material,
Lobat Tayebi, Zahra Zamanipour, Masoud Mozafari, Payam Norouzzadeh, Kenneth F.
Ede, Jerzy S. Krasinski, Daryoosh Vashaee, IEEE Green Technologies Conference
2012 - Energy Generation & Storage Technologies, Tulsa, Oklahoma, April 19-20,
2012
22.
Economical Preparation of Nanostructured Bulk (BixSb1-x)2Te3
Thermoelectrics,
Arash Mehdizadeh Dehkordi, Daryoosh Vashaee, IEEE Green Technologies Conference
2012 - Energy Generation & Storage Technologies, Tulsa, Oklahoma, April 19-20,
2012
23.
Increase of Boron Precipitation in Nanostructured P-type Silicon Germanium
Thermoelectric Alloys,
Zhaihui Gao, Zahra Zamanipour, Daryoosh Vashaee, IEEE Green Technologies
Conference 2012 - Energy Generation & Storage Technologies, Tulsa, Oklahoma,
April 19-20, 2012
24.
Enhancement of Doping Concentration in P-Type SiGe Thermoelectric Alloy with the
Addition of CrSi2,
Parvaneh Rouhani, Zahra Zamanipour, Jerzy S. Krasinski, Daryoosh Vashaee, Lobat
Tayebi, IEEE Green Technologies Conference 2012 - Energy Generation & Storage
Technologies, Tulsa, Oklahoma, April 19-20, 2012
25.
Enhancement of Thermoelectric Figure-of-Merit by a Nanostructure Approach,
Zhifeng Ren, Bed Poudel, Yi Ma, Yucheng Lan, Xiaowei Wang, Giri Joshi, Gaohua
Zhu, Jian Yang, Bo Yu, Xiao Yan, Hui Wang, Dezhi Wang, Qing Hao, Hohyun Lee,
Austin Minnich, Andrew Muto, Daryoosh Vashaee, Mildred Dresselhaus, Gang Chen,
Annual American Physical Society Meeting, March 16-20, 2009, Pittsburgh, PA.
26.
Mechanism of Enhancement of Thermoelectric Figure-of-Merit in Nanocrystalline
Materials,
Daryoosh Vashaee, Austin Minnich, Qiang Hao, Andrew Muto, Xiaoyuan Chen, Bed
Poudel, Yi Ma, Yucheng Lan, Bo Yu, Xiao Yan, Dezhi Wang, Z. F. Ren, Junming Liu,
Mildred S. Dresselhaus, Gang Chen, Japan-U.S. nanotechnology symposium, July
2008, Boston, Massachusetts.
27.
Thermoelectric Transport In Silicon Germanium Nanocomposite,
Hohyun Lee, Daryoosh Vashaee, Xiaowei Wang, Giri Joshi, Gaohua Zhu, Dezhi Wang,
Zhifeng Ren, Sabah Bux, Richard Blair, Pawan Gogna, Jean-Pierre Fleurial, Ming
Y. Tang, Mildred S. Dresselhaus, Gang Chen, ASME International Mechanical
Engineering Congress and Exposition IMECE October 31 – November 6, 2008, Boston,
Massachusetts.