Exploration and Optimization of Tellurium‐Based Thermoelectrics

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The power factor (PF) measurements for both doped trials can be examined in the following diagram. The first noticeable trait of the plots is that the largest power factor in both cases belongs to SnBi2Te4; a maximum value of 7.8 W∙cm ‐1 K ‐2 is obtained at 412 K. Any form of doping attempted lowers the magnitude of the PF similarly for both Ga and In trials. The doped magnitudes display no logical order. Though the Ga trials show no additional trends, one notices that the In trials shift their S max towards lower temperatures with increasing [In]. With x = 0.01, a maximum value is reached around 380 K (5.05 W∙cm ‐1 K ‐2 ), but x = 0.05, 0.07 reach maxima around 300 K (263/453 W∙cm ‐1 K ‐2 respectively). Figure 8.6 Power factor data for Ga‐doped (left) and In‐doped (right) samples of [Tr] xSn 1‐xBi 2Te 4. Measurements on selected thermal conductivity pellets reveal that there is little change in the behaviour of the doped samples. The magnitudes of the measurements, slopes of the curves and initiation of the bipolar conductivity are all seemingly unaffected by Ga‐ or In‐doping. The one exception to this evidence is In0.07Sn0.93Bi2Te4 which shows values between 0.5 and 1 W∙m ‐1 K ‐1 . This abnormality is found in three out of eighteen similar measurements on SnBi2Te4 and is likely experimental error due to a malfunction in the IR detector. 92
Figure 8.7 Thermal conductivity (left) and dimensionless ZT (right) for [Tr] xSn 1‐xBi 2Te 4. The highest ZT value belongs to the initial ternary compound, SnBi2Te4. Its maximum value of ~0.34 is found around 420 K, which is also the ZT max temperature for all the doped samples. With the minute changes observed in the DOS (bottom left of Figure 8.3) however, these physical property results are not entirely unexpected – the extra states from Ga for example, blend with the other orbitals and the band gap remains similar to that of the ternary. Ignoring 0.07 In which possess abnormally low thermal conductivity, the Ga‐based samples display a better on average than the In samples; these maximum values can be as low as 0.1 in the case of 0.05 In. 8.3.3.2. Substitution Samples Substitution reactions were also synthesized according to [Tr]xSnBi2‐xTe4, Tr = Ga, In, Tl and [V]xSnBi2‐xTe4, V = Nb, Ta. Samples were prepared as the reactions above. Substitution of the Bi atoms allows for potential atom size differences whist maintaining the compound’s initial electron counts. Ideally, the procedure would lower the thermal conductivity properties whilst keeping the power factor reasonably high. The ZEM results for selected sample measurements are contained below in Figure 8.8 with the heavy elements displayed in separate graphs for ease of data‐interpretation. The lighter substitution elements Ga and In are displayed in the bottom half of the figure with SnBi2Te4 for comparison. Unlike the previously discussed doped materials, almost all Seebeck coefficients were measured as smaller than SnBi2Te4. The lowest S values are found with x = 0.05 Tr, each of which has essentially the same magnitude at room temperature: ~65 V∙K ‐1 . It is quite clear from the diagrams that all measurements show very similar shapes and that there is no logical order in the Seebeck coefficients for any of the trials. The same can be said for σ values which also show the same curve shape as the ternary, albeit a 93
Page 1 and 2:
Exploration and Optimization of Tel
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Abstract Thermoelectric materials a
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Acknowledgements To begin, I would
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Table of Contents List of Figures..
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9.3.1. Heating, XRD, and Structural
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List of Figures Figure 1.1 (a) Pelt
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Figure 9.2 Selected DOS calculation
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List of Equations Equation 1.1 Dime
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Table B.1 Atomic positions, isotrop
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Section I: Fundamentals Background
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Opposing the Peltier Effect is the
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Hence it follows that a good thermo
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a b ∗ Equation 1.4 (a) Ele
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Historically, thermoelectric materi
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1.3.2. Advantages and Disadvantages
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common stoichiometry studied with c
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Figure 1.8 (a) Ge Quantum Dots [74]
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Chapter 2. Background of the Solid
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2.2. Defects, Non‐Stoichiometry a
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electric field draws electrons towa
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∑ known as a Bloch function, w
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orbital Hamilton population [96] i
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2.5.1. Doping and Substitution: Tun
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The major problem with exclusively
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Chapter 3. Synthesis Techniques All
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Since reactions are driven by both
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Table 3.1 Commonly used fluxes. [12
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The procedure is carried‐out on a
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Chapter 4. X‐Ray Diffraction Anal
Page 59 and 60: The closely related electron densit
Page 61 and 62: The majority of samples emerge from
Page 63 and 64: int ∑ mean ∑ | | Equat
Page 65 and 66: 4.3.1. Rietveld Method In 1967, Hug
Page 67 and 68: Chapter 5. Physical Property Measur
Page 69 and 70: The electrical conductivity, σ, is
Page 71 and 72: a p b 0.1388 53 c Equati
Page 73 and 74: measurement implies that there was
Page 75 and 76: Figure 5.6 Home‐made electrical c
Page 77 and 78: The SEM is constructed from an elec
Page 79 and 80: The EDX measurement system utilized
Page 81 and 82: 2 4 ext Equation 6.2 Ma
Page 83 and 84: Section III - Layered Bi2Te3 Compou
Page 85 and 86: aforementioned studies address the
Page 87 and 88: Pb‐based compound (~‐60 V∙K
Page 89 and 90: also differ in 2 there, while the r
Page 91 and 92: Table 7.2 LeBail data for phase‐p
Page 93 and 94: The physical properties, as mention
Page 95 and 96: Upon examination of the power facto
Page 97 and 98: Sn2Bi2Te5 was eventually found pure
Page 99 and 100: From the understanding of this comp
Page 101 and 102: Table 8.1 Rietveld refinements on S
Page 103 and 104: Although there is evidence here of
Page 105 and 106: Figure 8.3 DOS calculation comparis
Page 107 and 108: In order to better determine if the
Page 109: 8.3.3. Physical Property Measuremen
Page 113 and 114: the thermal conductivity slope that
Page 115 and 116: 8.4. Conclusions and Future Work A
Page 117 and 118: in Chapter 3 (except Arc Melting) w
Page 119 and 120: Table 9.2 LeBail refinements on var
Page 121 and 122: 9.2.3.1. Doping Trials: [Tr]xSn1‐
Page 123 and 124: 9.2.3.2. Substitution Trials: [Tr]x
Page 125 and 126: One can observe a variety of grain
Page 127 and 128: 9.2.5. Conclusions Drawn from SnBi4
Page 129 and 130: SnBi4Te7, but suggest similar albei
Page 131 and 132: 9.4. Project Summary and Future Wor
Page 133 and 134: Chapter 10. Introduction to Tl5Te3
Page 135 and 136: Figure 10.2 DOS calculations for Tl
Page 137 and 138: Thallium‐based chalcogenides clea
Page 139 and 140: : 36.3 (expected: 48.8 : 13.8 : 37.
Page 141 and 142: sintering of these pellets. A cold
Page 143 and 144: Figure 11.2 Thermoelectric properti
Page 145 and 146: at 319 K, increasing smoothly to 0.
Page 147 and 148: purity upon the first heating with
Page 149 and 150: Tl/Sn/Bi present in the 4c Wyckoff
Page 151 and 152: V∙K ‐1 at 592 K. As the bismuth
Page 153 and 154: Electrical conductivity values are
Page 155 and 156: Chapter 13. Modifications of Tl9SbT
Page 157 and 158: Table 13.1 Rietveld refinements for
Page 159 and 160: make an observable trend despite th
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The electrical conductivity values
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Section V - Ba Late‐Transition‐
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Obviously, compounds possessing the
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Table 14.1 Known Ba‐Cg‐Q compou
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All samples were analyzed by means
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crystal structure study of the Se
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As emphasized in Figure 15.2 (b), t
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The Cu-Cu COHP curve, cumulated ove
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Chapter 16. Ba3Cu17‐x(S,Te)11 and
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the selenide‐telluride before, th
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surrounded by three Q1 atoms. Besid
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Figure 16.3 The three‐dimensional
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Figure 16.5 Seebeck coefficient (le
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Chapter 17. Ba2Cu7‐xTe6 17.1. Int
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Table 17.1 Crystallographic Data fo
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Table 17.2 Atomic coordinates, Ueq
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17.3.2. Electronic Structure Calcul
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Figure 17.6 Crystal orbital Hamilto
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Section VI - Supplementary Informat
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[33] Rowe, D. M.; Kuznetsov, V. L.;
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[90] Albright, T. A.; Burdett, J. K
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[156] Cottenier, S., Density Functi
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[219] Toure, A. A.; Kra, G.; Eholie
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[294] Kanno, R.; Ohno, K.; Kawamoto
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Table A.3 Atomic positions and Ueq
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Table B.2 Selected interatomic dist
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Table B.5 Atomic coordinates and Ue
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Table B.7 Selected interatomic dist
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Exploration and Optimization of Tellurium‐Based Thermoelectrics

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