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- 1. Formation of Bismuth-Lead Telluride Widmansttten
Precipitates in Thermoelectric PbTe Marcus B. Toussaint1Teruyuki
Ikeda2, G. Jeffrey Snyder2 1Mechanical Engineering, Louisiana State
University, Baton Rouge, LA 708032Materials Science, California
Institute of Technology, 1200 E. California Blvd., Pasadena, CA
91125
- 2. Background Schematic of aThermoelectric Devicethermoelectric
generator Apply T, obtain V or vice versa dVSeebeck coefficient:S
dT Energy provided to the loadEfficiency: =Heat energy absorbed at
hot junctionf (zT ) 2 S Reduce lattice component byzT T
introduction of nanostructureThermal Conductivity given by: l
e
- 3. InspirationPbTe + Sb2Te3Lamellar Structure
- 4. MotivationPhase DiagramWidmanstatten precipitants formedin
5.5 at.% PbTe-Sb2Te3 system.
- 5. GoalsObtaining Precipitation PbTe-Bi2Te3 System
WidmanstttenBi-Pb-Te Phase Diagram (2002 Karpinskii O.G.)ASM Alloy
Phase Diagrams Center, P. Villars, editor-in-chief; H. Okamotoand
K. Cenzual, section
editors;http://www.asminternational.org/AsmEnterprise/APD, ASM
International,Materials Park, OH, USA, 2007Bi-Pb-Te Phase Diagram
(1967 Hirai T.)ASM Alloy Phase Diagrams Center, P. Villars,
editor-in-chief; H. Okamoto and K. Cenzual, section
editors;http://www.asminternational.org/AsmEnterprise/APD, ASM
International, Materials Park, OH, USA, 2007
- 6. Procedures (Bridgman Method): ampoule0.373mm/hrPeritectic
hot zone Eutectic (800C)L crystal cold zone 14% Pb in
PbTe-Bi2Te3FurnaceAnalysis done by SEM and EDS
- 7. Effect of Bi Concentration (Bridgman)35.00PbTe phase
1-2-430.0025.00 WidmanstaettenBi conc.
(at.%)20.0015.00PbBi2Te410.00 5.00 0.000 2 4 6810 12Distance from
the bottom / mmNo PrecipitationPrecipitationPbBi2Te4 phase
- 8. Widmansttten PrecipitationPbTeStructureMatrix (Bright):
PbTePrecipitates (Dark): PbBi2Te4
Pb(red)Te(blue)Bi2Te3StructureBi(green) 4 m Te(blue)4 directions:
crystallographicplanes
- 9. Phase Boundary and SolubilityBi-Pb-Te Phase Diagram (2002
Karpinskii O.G.) Bi-Pb-Te Phase Diagram (1983 Chami R.) Bi-Pb-Te
Phase Diagram (1967 Hirai T.) Examine by diffusion couple
- 10. Procedures (Diffusion Couple)Synthesize Pure PbTe and pure
Bi2Te3Homogenization PbTe : 550C for 1d Bi2Te3: 400C for
1dConditions Bi2Te3 3mm Bonding: 520C for 30 mins6mm Annealing:
550C for 15 hours PbTe Annealing: 450C for 9 days
- 11. Isothermal Annealing8 at.% Bi in
PbTe-Bi2Te3HomogenizedAnnealed
- 12. Analysis of Size ScaleMeasure Ferrets diameter of all
platesSum lengths of all platesMeasure area of photoComparison of
Bi system to Sb system1.5Length per area (m-1) 1.25 5.5 at.% SB8
at.% Bi 1 0.750.5 0.25 0600 650 700 750 800Temperature (K)
- 13. ConclusionsWidmansttten precipitants were obtained in bulk
forthe PbTe-Bi2Te3 based system.Solubility decrease as a function
of temperature forPbBi2Te4 in PbTe
- 14. AcknowledgmentsDr. Jeff SnyderDr. Teruyuki Ikeda Nathan J.
Marolf Kristin BergumNick A. Heinz Thermoelectrics group at Caltech
MURF program
- 15. Formation of Bismuth-Lead Telluride Widmansttten
Precipitates in Thermoelectric PbTe Marcus B. Toussaint1Teruyuki
Ikeda2, G. Jeffrey Snyder2 1Mechanical Engineering, Louisiana State
University, Baton Rouge, LA 708032Materials Science, California
Institute of Technology, 1200 E. California Blvd., Pasadena, CA
91125