Characterization and modeling of nanocomposite thermoelectric materials system bismuth antimony telluride ((Biy̳Sb1̳-̳y̳)2̳Te3̳) as a function of temperature and magnetic field

This thesis looks at (BiySb1-y)2Te3 nanocomposites as an example of the currently available nano systems. In this thesis, (BiySb-y)2Te3 nanocomposites are characterized from ~325K down to ~3K. Advantages of this low temperature regime include the minimization of lattice vibrations and the decreasing of ke with decreasing temperature. As a result, nano effects on IL could be better observed and characterized in this low temperature regime. We are also interested in studying the effect of an applied magnetic field on the conduction carriers in this low temperature regime. We like to find out whether an applied magnetic field could impede the carriers' heat conducting ability more than their current conducting ability. Therefore, a magnetic field effect study is also carried out to see whether any improvement in ZT could be achieved by the applying of a magnetic field. The measurement system used in this thesis is QD PPMS. Only the ACT and TTO options of the QD PPMS apparatus are used for measurements in this thesis. Under the ACT option, Hall and 4-pt p measurements on the same sample are performed. On the other hand, Kti, S, and 2-pt p measurements are performed simultaneously on the same sample under the TTO option. Both the ACT and TTO options use an AC current instead of a DC current during p measurement to eliminate any unwanted Seebeck voltage. Since the ability to perform correct measurements on thermoelectric samples is not a trivial task, benchmarking with known results is a must. In this thesis, I calibrate our QD PPMS against both the manufacturer's results and the published data, and demonstrate that our measurement system gives accurate results. I also benchmark our nt, results under a magnetic field using a pyrex sample. Our results confirm that the QD PPMS apparatus does not introduce artifacts under an applied magnetic field. Thus, any changes observed under the QD PPMS apparatus measurements in an applied magnetic field would be expected to be solely due to the sample. Lastly, no measurable difference is found between our 2-pt p (TTO) and 4-pt p (ACT) measurements. A total of eight (BiySb1-y) 2Te3 samples are measured in this thesis. The sample set includes: (a) one bulk ingot sample manufactured by Marlow (Ingot), (b) four nanocomposite samples (XY21, XY146, XY144, and GJ99) made by collaborators from Boston College (BC) where the letters simply indicate the sample maker's initials, and (c) three nanocomposite samples (0%, 40%, and 100%) made by collaborators from Nanyang Technological University (NTU) in Singapore, where the % denotes the weight % of the nanoinclusions prepared via melt spinning [1] in the sample. All the nanocomposite samples in this thesis are made solely for research uses and are purposely fabricated under conditions different than those used for the best samples previously reported [2, 1]. Although BC and NTU use different starting materials, different fabrication machines, and different fabrication parameters, the resulting densities of the nanocomposites from the ball-milled nanopowders alone (XY21, XY146, XY144, GJ99, and 0%) are almost identical. Moreover, the addition of nanoinclusions prepared via melt spinning decreases the sample mass density somewhat.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2011

Author dc:creator

• Tang, Ming Y., 1979-

Advisor dc:contributor.advisor

• Mildred S. Dresselhaus.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/68496

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/68496