1. 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. 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. 3. InspirationPbTe + Sb2Te3Lamellar Structure
4. 4. MotivationPhase DiagramWidmanstatten precipitants formedin 5.5 at.% PbTe-Sb2Te3 system.
5. 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. 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. 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. 8. Widmansttten PrecipitationPbTeStructureMatrix (Bright): PbTePrecipitates (Dark): PbBi2Te4 Pb(red)Te(blue)Bi2Te3StructureBi(green) 4 m Te(blue)4 directions: crystallographicplanes
9. 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. 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. 11. Isothermal Annealing8 at.% Bi in PbTe-Bi2Te3HomogenizedAnnealed
12. 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. 13. ConclusionsWidmansttten precipitants were obtained in bulk forthe PbTe-Bi2Te3 based system.Solubility decrease as a function of temperature forPbBi2Te4 in PbTe
14. 14. AcknowledgmentsDr. Jeff SnyderDr. Teruyuki Ikeda Nathan J. Marolf Kristin BergumNick A. Heinz Thermoelectrics group at Caltech MURF program
15. 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