Oxidische Materialien: ZrO 2

1. Oxidische Materialien: ZrO2 Jürgen Janek Carsten Korte, Ilia Valov, Robert Klein, Andreas Peters Bjoern Luerßen, Holger Fischer, Eva Mutoro Marcus Rohnke, Sebastian Meiss Funding: DFG, FCI, BASF AG DFG-Schwerpunktprogramm 1136 www.chemie.uni-giessen.de/home/janek

2. ZrO2 als elektrokeramisches Material • Die Elektrolytmembran (Energietechnologie) HT-Brennstoffzellen (SOFC) . . . . . Grenzflächenchemie. . . . . unkonventionelle Brennstoffe • Das Sensormaterial (Sensortechnologie) Elektrochemische Sensoren Ionische Langmuir-Sonden . . . . . . . . Plasmaanalytik • Die Ionenpumpe (Oberflächenchemie/Plasmachemie) Elektrochemische Promotion . . . . . . smart surfacesIonenpumpen für Plasmen . . . . . . . . Plasmatechnologie • Neue Materalien (und Funktionen…) Substitution/Dotierung . . . . . . . . . . . Stickstoffionenleiter . . . . . . . . . . Lumineszenz . . . . . . . . . . Nanoskalige Multischichten

3. ZrO2(+Y2O3) – Die „Nernstmasse“

4. ZrO2(+Y2O3) – Die Nernstlampe

5. Chemistry Physics Engineering Solid State Ionics – Open questions? • Bulk properties/phenomena: - Equilibrium defect structures - Non-equilibrium defects (low-T) - New electrolytes - Optimisation of functional materials • Interfacial phenomena: - surfaces of ionic solids - solid/solid electrodes - kinetics of inner boundaries - interfaces plasma/ionic material • Galvanic cells: - new sensors - new fuel cells/batteries - thermovoltaics • Methods: - in situ spectroscopy/microscopy - microelectrodes - micro- and nano-ionics

6. Electrochemical surface control Electrochemical generation of „spillover“ species • e. g. oxygen on platinum • e.g. sodium on platinum many studies - but no in situ studies on microscopic details Electrochemical „Switching“ of catalysts MeOx on YSZ - thin films of oxides (PLD) - e. g., Fe2O3→ Fe3O4→ Fe1-xO → Fe no investigations yet (to our knowledge…)

7. 350 µm Electrochemical surface control 0 s T = 400 °C p(O2) = 10-5 mbar 18,0 s Pt surface YSZ surface 18,8 s 19,6 s 20,4 s 21,2 s 22,0 s 22,8 s 24,0 s diffusion coefficient corresponding to work function front: D[Pt(111), 400°C]  5·105 cm2/s diffusion coefficient of atomic oxygen: DO[Pt(111), 200°C] = 5.2·106 cm2/s

8. Ionic transport in boundary regions s sGr 2d (sGr–sVol) sVol 1/d 1/d Ionic conductivity vs. layer periodicity insulator d interface sGr bulk d electrolyte sVol interface 2d (sGr–sVol) ≈ 2dsGrifsGr>>sVol electrolyte bulk

9. Ionic transport in boundary regions Overlap of space charge regions,strong increase in conductivity s c( ) sGr d < δ d = δ d > δ d [1] Sata, Eberman, Eberl und Maier, Nature 408, 946-949 (2000) [2] Sata, Jin-Philipp, Eberl und Maier, Solid State Ionics 154-155, 497-502 (2002) 2d (sGr–sVol) sVol (in the case of CaF2/BaF2 für d > 50 nm) 1/d 1/d c( ) structural disorder,small change of σGrwith periodicity d < δ d = δ d > δ d or

10. Ionic transport in boundary regions U porousPt-electrode jO2- porousPt-electrode SEM images 500 nm ½ O2 + 2 e– = O2– O2– = ½ O2 + 2 e– substrate 500 nm Al2O3 ZrO2/Al2O3 ZrO2 I Al2O3 Al2O3 500 nm 2 µm Pulsed Laser Deposition: systems: ZrO2(+ 12 mol% CaO) / Al2O3 • high concentration of mobileoxygen vacancies • small Debye length, lD ≈ 10 nm

11. Ionic transport in boundary regions 200 nm 100 nm 67 nm 50 nm 40 nm 33 nm conductivity increases with 1/d by 2 orders of magnitude Interface: 2δσGr ≈ 2,4 · 10-9 S (600 °C) δ < 10-9 m(TEM results) σGr ≈ 1,2 · 10-2 S/cm (600 °C) cf. σVol ≈ 6,0 · 10-6S/cm about 4 orders of magnitude conductivity reciprocal thickness ZrO2 (+ 12 mol% CaO) / Al2O3

12. Ion emission from YSZ Y. Torimoto et al., Jpn. J. Appl. Phys. 36 (1997) L238 Y. Fujiwara at al., J. Electrochem. Soc. 150 (2003) E117

13. Ion pumping into plasmas

14. Ion pumping into plasmas Parallelplattenentladung: - kapazitiv, asymmetrisch - f = 13,56 MHz max. Ueff ~ 600 V Arbeitsgas : Sauerstoff - p = 5 - 100Pa - Gasfluß= 3 - 10 sccm Optisches System: - Nd:YAG gepumter Farbstofflaser (10 Hz / 355 nm) - Farbstoff : 1:1 Mischung Coumarin 47/ 120 - Filter : (846 + 3) nm Electrodes: - radius r = 40 mm, - distance d = 15 - 100 mm Resolution: axial: - max. shift 100 mm, - min. step size 0,3 mm, - min. distance beam-electrodes 0,5 mm radial: - max. shift 76 mm, - min. sep size 1 mm Institut für Physik Universität Greifswald TALIF-Experiment

15. Ion pumping into plasmas oxygen atom density YSZ electrode steel electrode M. Rohnke, S. Peters, J. Janek and J. Meichsnersubmitted to J. Appl. Phys. (2004)

16. (Zr,Y)(N,O)2 – A nitrogen electrolyte annealed at 700 °C for 15 min 15 min at 700 °C applied voltage U = -2.2V 1 cm as-deposited as-deposited films show dark violet color SIMS analysis proofs that nitrogen remains in YSZ after annealing (i.e. the violet color is related to reduction of YSZ)

17. (Zr,Y)(N,O)2 – A nitrogen electrolyte as-deposited (500 °C deposition temperature) 18O / (16O + 18O) YSZ/Al2O3 Multilayers 100nm/layer YSZ YSZ/Al2O3 Multilayers 100nm/layer

18. (Zr,Y)(N,O)2 – A nitrogen electrolyte thermally annealed 700 °C, 15 min 18O / (16O + 18O)

19. (Zr,Y)(N,O)2 – A nitrogen electrolyte field experiment 700 °C for 15 min U = -2.2 V oxygen is much faster than nitrogen The applied electric field influences the nitrogen profile… 18O / (16O + 18O)

20. Dr. Bjoern Luerssen Dr. Marcus Rohnke Bernhard Franz Ilia Valov Robert Klein Boris Mogwitz Dr. Carsten Korte Prof. Jürgen Janek Klaus Peppler Eva Mutoro Claus C. Fischer Sebastian Meiß Andreas Peters Holger Fischer Dr. Doh-Kwon Lee

21. www.chemie.uni-giessen.de/home/janek