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Enhanced Thermoelectric properties via oxygen non- stoichiometry and strain of La 2 NiO 4+ δ

Enhanced Thermoelectric properties via oxygen non- stoichiometry and strain of La 2 NiO 4+ δ. Financial support from :. Project MAT 2009-08165 Ramón y Cajal Program. Víctor Pardo, Antía S. Botana, Daniel Baldomir , PRB 86, 165114 (2012).

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Enhanced Thermoelectric properties via oxygen non- stoichiometry and strain of La 2 NiO 4+ δ

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  1. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Financialsupportfrom: Project MAT 2009-08165 Ramón y Cajal Program Víctor Pardo, Antía S. Botana, Daniel Baldomir, PRB 86, 165114 (2012). Víctor Pardo, Antía S. Botana, Daniel Baldomir, PRB 87, 125148 (2013). Víctor Pardo March Meeting, Baltimore 2013

  2. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Daniel Baldomir Antía S. Botana Francisco Rivadulla’sgroup: Paul L. Bach J.M. Vila-Fungueiriño V. Leborán Víctor Pardo March Meeting, Baltimore 2013

  3. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Thermoelectric figure of merit (dimensionlessquantity): zT= σS2T/κ zT= σS2T/κ - Goodelectrical conductor - Poorheat conductor - Largethermopower zT > 1 forapplications σT/κ ~ constantformetals → S= 160 μV/K toreachzT= 1. S > 100 μV/K for a high-performance thermoelectric material Picture takenfrom: Sensors and Actuators A: Physical 145-146, 423 (2008). Víctor Pardo March Meeting, Baltimore 2013

  4. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Methods • - Ab initio electronicstructurecalculations (DFT-based) • WIEN2k package. • Full-potential, all-electroncalculations. • Comparison of threeexchange-correlationpotentials: GGA, LDA+U, Tran-Blahamodifiedversion of theBecke-Jonssonpotential. • TransportpropertiescalculatedusingBoltzTrap. • Weusedthevirtual crystalapproximationtosimulatedopingeffects. • Structuraldetailstakenfromexperiment. Víctor Pardo March Meeting, Baltimore 2013

  5. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Misfitlayeredcobaltates: NaxCoO2 Highthermoelectric performance Existence of twoelectronicsystems Víctor Pardo March Meeting, Baltimore 2013

  6. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ dz2 La2NiO4layeredcompound Ni2+: d8 S=1 dx2-y2 dxy dxz,yz Víctor Pardo March Meeting, Baltimore 2013

  7. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ dz2 dx2-y2 dxy dxz,yz J.B. Goodenough et al., Mat. Res. Bull. 17, 383 (1982). Víctor Pardo March Meeting, Baltimore 2013

  8. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 zT= σS2T/κ σ/κconstantformetals S2enoughtoanalyzetrends T= 400 K La2NiO4+δ Seebeck vs. hole-doping concentrationδ Peaks at aboutδ= 0.05 Negativethermopower at higher doping Víctor Pardo March Meeting, Baltimore 2013

  9. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 Sr6Co5O15: A.S. Botana et al., PRB 83, 184420 (2011) CrN: A.S. Botana et al., PRB 85, 235118 (2012) Víctor Pardo March Meeting, Baltimore 2013

  10. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ At smallhole-doping concentration, thereis a peak in thermoelectric figure of merit Figure of merit: zT= σS2T/κ Víctor Pardo March Meeting, Baltimore 2013

  11. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Promisinghigh-temperaturebehaviorwith S > 100 μV/K forδ~ 0.05. VCA calculations Víctor Pardo March Meeting, Baltimore 2013

  12. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ zT= σS2T/κ Calculatedelectronic-only figure of merit shows promisingvalues at high T forδ~ 0.05. Calculations do notincludethermalconductivityduetophonons (largestcontribution !!) Víctor Pardo March Meeting, Baltimore 2013

  13. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 Comparisonwithavailableexperiments: difficultduetolack of systematics vs. δ - Largethermpower at low-doping - Crossingtowardsnegativevalues at higher-doping levels - S increases at high T and intermediatedopings Víctor Pardo March Meeting, Baltimore 2013

  14. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 zT= σS2T/κ Usingσ/κconstantfrom experimental values and S calculated. Weestimate a figure of meritzT ~ 0.1 at high T and δ~ 0.05, can thisbeimproved? Víctor Pardo March Meeting, Baltimore 2013

  15. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Can tensilestrainimprovezT ? Try tolowertheenergy of the x2-y2 band and utilizethelocalized z2 band (large S) Valencebandsgetclosertogetherwhen a isincreased Víctor Pardo March Meeting, Baltimore 2013

  16. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Values of thelatticeparameter a= 3.95 – 4.00 A (tensilestrain: LNO’s a= 3.86 A) leads toenlargedthermopower zT= σS2T/κ Víctor Pardo March Meeting, Baltimore 2013

  17. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Values of thelatticeparameter a= 3.95 – 4.00 A (tensilestrain) lead tolargeelectronic-only figure of merit, forδ~ 0.05 – 0.10 Víctor Pardo March Meeting, Baltimore 2013

  18. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ Experimentsconfirmthattensilestrainin thin films of differentthicknesses (differentstrains) drives thesystemtowards a largerthermopowerwithoutcompromisingtheconductivity (in fact, decouplingthem) [Paul L. Bach’stalkonWednesday N12.12] Víctor Pardo March Meeting, Baltimore 2013

  19. Enhanced Thermoelectric properties via oxygen non-stoichiometry and strain of La2NiO4+δ • Summary: • La2NiO4+δ can be a possiblecandidateforhigh-performance thermoelectric at high T if doping and strain are optimized. • Seebeckcoefficients up to 200 μV/K can beobtainedaboveroomtemperaturefortheappropriatetensilestrain. • Conductivity and thermopower can bedecoupledviastrainengineering ! • Control of thestoichiometryis a new pathtoimprovethermoelectricefficiency in oxides in general. Víctor Pardo March Meeting, Baltimore 2013

  20. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3-δ Theagreementisreasonablygoodforthedopantconcentrationsanalyzed (experimentallyobtainedvia Hall effectmeasurements) Verylargethermopowerisobtained in thatvery light electrondopedregion (as aneffect in thebulk) Víctor Pardo March Meeting, Baltimore 2013

  21. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3-δ Verylargethermopower in STO-2DEG, really a 2D effect? Víctor Pardo March Meeting, Baltimore 2013

  22. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3-δ STO substratestreated in orderto tune theoxygencontent VerylargeSeebeckisobserved in pure SrTiO3-δ Theeffectis in a bulk (0.5 mm substrate) See: P.L. Bach et al., arxiv/1211.1615 Víctor Pardo March Meeting, Baltimore 2013

  23. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3-δ Westudy a very light doping case, only 1 oxygenvacancy per 106sites We explore thevery light electron-dopedbulk STO via ab initio calculations Víctor Pardo March Meeting, Baltimore 2013

  24. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3-δ Thermalconductivityisstronglysuppressedbytheintroduction of scattering centers throughoxygenvacancies Similar reductionduetooxygenexcesscouldbe active for La2NiO4+δ Víctor Pardo March Meeting, Baltimore 2013

  25. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3-δ SrTiO3-δ La2NiO4+δ Víctor Pardo March Meeting, Baltimore 2013

  26. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 • i) Thin film geometry: • largeconductivityincreaseduetothelarger in-planeconductivity • expectedreduction of thethermalconductivity • willtheSeebeckcoefficient of thin films bedifferent? Furthercalculationsneeded in 2D. Víctor Pardo March Meeting, Baltimore 2013

  27. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 Víctor Pardo March Meeting, Baltimore 2013

  28. Thermoelectric properties of La2NiO4+δ from ab initio techniques S increases as σdecresases, so weneedtoanalyzethemcombined, e.g. in theform of thepower factor S2σ. Highestvalues at thelowerlatticeparameter (weneedtoanalyzecompressivestrain). Víctor Pardo Davis, June 2012

  29. Thermoelectric properties of La2NiO4+δ from ab initio techniques Thank you for your attention Víctor Pardo Davis, June 2012

  30. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 Seebeckcoefficientsgetlarger (as conductivitydecreases) Bandsbecome more closertogether and thepeak in S vs. p startstobesmearedout Víctor Pardo March Meeting, Baltimore 2013

  31. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 For a sufficientlylarge, bandsget so closetogetherthatthebehavioristhat of a standard semiconductor, similar towhatwouldbeobtainedforCrN Lack of intermediate-doping high S values Víctor Pardo March Meeting, Baltimore 2013

  32. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 Víctor Pardo March Meeting, Baltimore 2013

  33. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 Víctor Pardo March Meeting, Baltimore 2013

  34. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 Víctor Pardo March Meeting, Baltimore 2013

  35. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 S increases as σdecresases, so weneedtoanalyzethemcombined, e.g. in theform of thepower factor S2σ. Highestvalues at thelowerlatticeparameter (weneedtoanalyzecompressivestrain). Víctor Pardo March Meeting, Baltimore 2013

  36. Enhanced Thermoelectric properties via oxygen non-stoichiometry of La2NiO4+δand SrTiO3 a= 3.90 Å= 10.44 a.u. a= 3.85 Å= 10.29 a.u. a= 4.00 Å= 10.69 a.u. a= 3.8 0Å= 10.16 a.u. a= 4.11 A= 11.0 a.u. aexptal = 3.89 Å Víctor Pardo March Meeting, Baltimore 2013

  37. x2 -y2 ↓ z2 ↓ x2 -y2 ↑ xy ↑ z2 ↑ xy ↓ xz,yz

  38. Thermoelectric properties of La2NiO4+δ from ab initio techniques Na cobaltates: NaxCoO2, misfits, etc … Twotypes of electronswithdifferentbandwidths: goodconductivities and largethermpower G. Khaliullin and J. Chaloupka Víctor Pardo Davis, June 2012

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