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Study of Thermoelectric Properties of Lead Telluride Based Alloys and Two-Phase Compounds

Electronic Theses of Indian Institute of Science

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Title Study of Thermoelectric Properties of Lead Telluride Based Alloys and Two-Phase Compounds
 
Creator Bali, Ashoka
 
Subject Lead Telluride Alloys
Lead Telluride Alloy Thermoelectrics
Thermoelectric Materials
Two-Phase Compounds
Thermoelectric Figure of Merit
Thermoelectric Devices
Thermoelectric Power Generation
Thermoelectrics
Thermal Conductivity
Electrical Resistivity
Seebeck Coefficient
Lead Telluride-Bismuth Thermoelectrics
Lead Telluride-Indium Thermoelectrics
PbTe
Pb1−ySnyTe Alloys
PbTe1−ySey Alloys
Pb0.75−xMnxSn0.25Te
Materials Science
 
Description The growing need of energy worldwide has lead to an increasing demand for alternative sources of power generation. Thermoelectric materials are one of the ‘green energy sources’ which convert directly heat into electricity, and vice–versa. The efficiency of this conversion is dependent on ‘figure of merit’ (z T), which depends on the material’s Seebeck coefficient (S), electrical resistivity (ρ) and thermal conductivity (κ) through the relation z T=S2T/ρκ, where T is the temperature. High values of z T lead to high efficiency, and therefore, z T must be maximized. Lead telluride is well–established thermoelectric material in the temperature range 350 K and 850 K. The aim of this thesis is to improve the z T of the material by adopting two different approaches – (i) doping/alloying and (ii) introducing additional interfaces in bulk i.e. having two phase PbTe.
In this thesis, first an introduction about the thermoelectric phenomenon is given, along with the material parameters on which z T depends. A survey of literature associated with PbTe is done and the current status of thermoelectric devices is summarized briefly. This is followed by a description of the synthesis procedure and the measurement techniques adopted in this work.
The first approach is the conventional alloying and doping of the material by which carrier concentration of the material is controlled so that maximum power factor Sρ2 is achieved and a simultaneous reduction of thermal conductivity takes place by mass fluctuation scattering. Under this, two systems have been studied. The first system is PbTe1−ySey alloys doped with In (nominal composition: Pb0.999In0.001Te1−ySey, y=0.01, 0.05, 0.10, 0.20, 0.25, 0.30). The compounds were single phase and polycrystalline. Lattice constants obtained from Rietveld refinement of X–ray diffraction (XRD) data showed that Vegard’s law was followed, indicating solid solution formation between PbTe and PbSe. Compositional analysis showed lower indium content than the nominal composition. Temperature dependent Seebeck coefficient showed all the samples to be n–type while Pisarenko plots showed that indium did not act as a resonant dopant. Electrical resistivity increased with temperature, while mobility vs T fitting showed a mixed scattering mechanism of acoustic phonon and ionized impurity scattering. Thermal conductivity followed a T1 dependence, which indicated acoustic phonon scattering. At high temperature, slight bipolar effect was observed, which showed the importance of control-ling carrier concentration for good thermoelectric properties. A z T of 0.66 was achieved at 800 K.
The second alloy studied under this approach was Mn doped Pb1−ySnyTe alloy (nominal composition Pb0.96−yMn0.04SnyTe (y=0.56, 0.64, 0.72, 0.80)). All the samples followed Vegard’s law, showing formation of complete solid solution between PbTe and SnTe. Microstructure analysis showed grain size distribution of
 
Contributor Mallik, Ramesh Chandra
 
Date 2018-01-02T20:03:33Z
2018-01-02T20:03:33Z
2018-01-03
2014
 
Type Thesis
 
Identifier http://hdl.handle.net/2005/2950
http://etd.ncsi.iisc.ernet.in/abstracts/3812/G26672-Abs.pdf
 
Language en_US
 
Relation G26672