Role of structures on thermal conductivity in thermoelectric materials C. Godart, A.P. Gonçalves, E.B. Lopes, B. Villeroy, E. Alleno, O. Rouleau CNRS UMR7182- ICMPE / CMTR- Thiais, France Dep. Química, I.T.N.- Sacavém, Portugal Thanks to Velijko Acknowledgments: Franco-Portuguese Program GRICE N° 20157 (2007-2008) 1 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart Recent evolutions 2007: CNRS GDR TE (founding labs: Bordeaux, Caen, Montpellier, Nancy, Thiais) LOCIE (building) Industrials join the meetings program "Energie 2" (CNRS) Hope it will help to include "thermoelectric" word in 7 th PCRD 2008: 140 participants in European TE Conf. publications on line: (http://ect2008.icmpe.cnrs.fr/) 2 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart
Properties and Applications Applications Applications Applications OUTLINE of Therm oelectric Materials * Crystallography bonding, distances, cages HVAR 2 0 0 8 ZT, σ , S, semiconductor λ Thermal conductivity: electronic λ él lattice λ latt , * Classical TE materials (semiconductor) * Various effects of structure to decrease λ latt ADP - few cage like structures Few complex structures * Conducting glass (Gonçalves) Micro composites new Nano Nano materials (1, 2D) Sales Nano composites * Shaping (SPS) - applications 3 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart NaCl F (225) CsCl P (221) Structure - bonding FCC compact CC non compact a= 5.64 a=6.17 Cl Cl Cl Cl Cl Cl Na Na Cl Cl Na Na Cl Cl Na Na Cl Cl Cl Cl Cl Cl Na Na Cl Cl Na Na Cl Cl Na Na Coordinence Cl Cl Na Na Cl Cl Cs Cs 8 Na Na Cl Cl Na Na 6 Cl Cl Na Na Cl Cl Cl Cl Cl Cl Na Na Cl Cl Na Na b b Cl Cl Na Na Cl Cl Cl Cl Cl Cl a a c c PowderCell 2.0 PowderCell 2.0 PowderCell 2.0 PowderCell 2.0 No atom1 atom2 distance No atom1 atom2 distance -------------------------------------- -------------------------------------- 1 Cl Na 2.8200 1 Cl Cs 3.5707 2 Na Na 3.9881 Distances between atoms - (distance (A1-A2)- radius A2) >> radius A1 : possibility of cage around A1 - different distances around atom A on sites 1 , 2 : possibility of cage 4 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart
Atomic Displacement Parameters (ADP) atom A (T ≠ 0) moves atomic displacement parameter : mean square displacement amplitudes / equilibrium generally non isotropic U ij (ellipsoids of movement of the atoms) mean value in all directions U iso (check atoms with strong vibrations) U iso (T) ↑ si T ↑ if U iso (T->0) ≠ 0: possibility of static disorder 5 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart Peltier ( Π ) Seebeck (S) 2 TE effects (1822 à 1850) ∆ T=T c -T f T c ∆ T => ∆ V I => Q T f ∆ V = S. ∆ T Q = Π . I XXX electricity generation cooling thermocouple S: Seebeck coefficient = entropy per charge carrier / charge, N(E F ) Thompson (Lord Kelvin) Π = S . ∆ T = Q / I 6 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart
Hot zone T h Cold T c Heat Flux h+ h+ e- e- I I Heat sink T c Hot zone T h Load Cooling Generation TE Couple 2 materials: type p & type n Device: chemically loving materials 7 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart FIGURE of MERIT ZT ) maximum of ZT = S 2 σ T / λ GOOD electric conductor BAD thermal conductor!! Optimize transport properties of materials Cooling: electricity generation : ( )( ) − γ − 1 γ − T T = η T T h c = ( )( ) COP c h γ = (1+ZT) 1/2 + γ max − + γ 1 T T T T c h c h σ S 1- increase the power factor : S 2 σ S 2 σ Isolant Métal S decreases ~ log (n, p) σ increases ~ (n,p) Semiconducteur Semiconductor 14 1016 1018 20 22 10 10 10 Carrier content 2- decrease the thermal conductivity : λ λ = λ él + λ latt Play on phonons DO NOT affect σ 8 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart
Effects on phonons Materials Complex Increase the optical phonons modes Clathrate structure (heat carried by 3 acoustic modes & Chevrel (SC) less by 3(N-1) optical modes Intermet.Yb 14 MnSb 11 Skutterudite Weakly bound Increase disorder Skutterudite atoms (or out of Clathrate positions ) Penta-telluride Solid solutions, Increase mass fluctuations + half Heusler vacancies Impurities, Increase diffusion Bi 2 Te 3 +Te+CuBr inclusions Zn 4 Sb 3 PbTe -TAGS composites Grains Reduce the mean free path of Nano-materials boundaries phonons (PbTe+TAGS), low dimensionality G. Slack, TE handbook 1995 see A.P. Gonçalves, Conducting glass- Hvar 2008 9 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart Thermoelectric materials (from inefficient to better..) Known Systems in 1960 …& in 1990 !!! Semicond. Bi-Sb (Bi,Sb) 2 (Te,Se) 3 PbTe TeAgGeSb Si-Ge T use (K) 200 ~300 /GAP/ 700 750 ~1000 ZT at T use 1.1 (H) 0.9 0.8 1.1 0.6 Cooling electricity generation ZT=3.5 35 Efficacité Maximum η (%) ZT=3 Materials: 30 ZT=2.5 ZT=2 25 1-better ZT ZT=1.5 20 ZT=1 2-stable at T ↑ 15 10 3-ZT ↑ in [T] ↑ 5 ZT ∆ T 0 0 200 400 600 800 1000 1200 Température chaude (K) 10 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart
Thermoelectric materials (1960-90.. ) & ZT ≈ 1 2.2 2.0 T gap 1.8 1.6 1.4 (Bi,Sb) 2 (Se,Te) 3 1.2 ZT TeAgGeSb (Si,Ge) 1.0 0.8 PbTe 0.6 0.4 0.2 -200 0 200 400 600 800 1000 1200 T (°C) 11 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart New: Zn4Sb3 skutterudites complex clathrates Chevrel Oxides 2008 Thermoelectric materials: p- type 1.6 Zn 4 -x Cd x Sb 3 CeFe 3.5 Co 0.5 Sb 12 Zn 4 Sb 3 1.4 1.2 Ba 8 Ga 18 Ge 28 Bi 2-x Sb x Te 3 Yb 14 MnSb 11 1.0 Pb 1-x Sn x Te 1-y Se y 0.8 ZT Mo 3 Sb 7 +Te, Ru,Fe CuMo 6 Se 8 Si 0.80 Ge 0.20 0.6 0.4 Na x CoO 2 Borures β -FeSi 2 0.2 Godart- CNRS- 2008 Ca 3 -x Na x Co 4 O 9 0.0 0 200 400 600 800 1000 1200 1400 Temperature (K) 12 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart
New: skutterudites clathrates chalcogenides semi Heusler oxides 2008 Thermoelectric materials : n- type 1.6 In 0.2 Ce 0.2 Co 4 Sb 12 Ti 0.5 (Zr 0.5 Hf 0.5 ) 0.5 NiSn 0.998 Sb 0.002 Ba 8 Ga 16 Ge 30 LaTe 1.45 1.4 In 0.2 Co 4 Sb 12 Ba 0.3 Co 3.95 Ni 0.05 Sb 12 1.2 Bi 2-x Sb x Te 3 Pb 1-x Sn x Te 1-y Se y CoSb 3 1.0 Si 0.80 Ge 0.20 ZT 0.8 (Zn 0.98 Al 0.02 )O - UFP Bi 2 (Sb,Te) 3 0.6 In 2 0 3 +Ge 0.4 SrPbO 3 0.2 β -FeSi 2 0.0 0 200 400 600 800 1000 1200 1400 Temperature (K) 13 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart Cage compounds Specific heat LaB 6 : ADP (300K) => T Einstein of La & T Debye of B LaB 6 : La Einstein oscillator in Debye solid of B Used with success in various series of materials 14 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart
Lattice thermal conductivity, specific heat, T Debye , T Einstein Possible minimum value of lattice thermal conductivity ~ λ L =1/3C v v S d → 3 = C v specific heat estimated from Dulong & Petit law ( ) 3 C R N k A B → ∞ T v s speed of sound in the material d mean free path of phonons (sometimes chosen equal to lattice parameter) effects of T f = fraction lattice atoms (B), (1-f) fraction (La) C v = f C Debye + (1-f) C Einstein C Einstein contribution Ln to the molar specific heat C v C Debye contribution of lattice to C v ( ) θ 3 θ / T 2 ∫ = T D x e ⎛ θ ⎞ E 9 4 C N k x dx e T ( ) θ D B = ⎜ ⎟ 2 3 A − E 1 0 C N k ⎜ ⎟ e D E B x A 2 T ⎛ − ⎞ ⎝ ⎠ θ ⎜ E ⎟ 1 e T ⎝ ⎠ π 12 θ π 4 2 → → 0 : 0 k < θ T T C false : ~ ( ) B 3 D T C N k = E ( ) 5 θ v D D A B sound π 1 / 3 6 2 h n D → ∞ → : 3 → ∞ → T C N k : 3 T C N k D A B E A B 15 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart Skutterudites Sb Sb Sb Sb La La Sb Sb Sb Sb La La Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Co Co Co Co Physical Prop. Co Co Co Co Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Brian Maple Sb Sb Sb Sb Sb Sb La Sb Sb Sb Sb Sb Sb Sb Sb Co Co Co Co Sb Sb Sb Sb Sb Sb Peritectic => Sb Sb Sb Sb Sb Sb Co Co Co Co Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Preparation CoSb 3 - Im3 b La La Sb Sb Sb Sb La La c a PowderC Crystals LaFe 4 Sb 12 - Im3 Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Co Co Co Co Co Co Co Co Co Sb Sb Sb Sb Sb Sb Sb Sb Sb La La Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Co Co Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Co Co Co Co Co Co Co Co Co Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Co Co Sb Sb Sb Sb Sb La Sb Sb Sb Sb Sb Sb Co Sb Sb Sb Sb Sb Sb Co Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Co Co Co Co Co Sb Sb Co Co Co Co Co Co Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb Sb b b Sb Sb Sb Sb Sb Sb c La a c Powde Sb Sb Sb La a PowderCell 2.0 PowderCell 2.0 Ce-8Fe Ce-12Sb CoSb 3 cage 16 NATO ARW workshop Thermoelectrics- Hvar Sept. 2008- C. Godart
Recommend
More recommend
