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Oxidische Materialien: ZrO2

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Presentation on theme: "Oxidische Materialien: ZrO2"— Presentation transcript:

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

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 surfaces Ionenpumpen für Plasmen Plasmatechnologie Neue Materalien (und Funktionen…) Substitution/Dotierung Stickstoffionenleiter Lumineszenz Nanoskalige Multischichten

3 ZrO2(+Y2O3) – Die „Nernstmasse“

4 ZrO2(+Y2O3) – Die Nernstlampe

5 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 Chemistry Physics Engineering

6 Projects Surface chemistry Bulk transport and reaction
Plasma electrochemistry Electrochemical promotion of catalysis Electrochemical deposition of ceramic films Bulk transport and reaction Electromigration Field-driven reactions Ionic thermoelectricity Thermodiffusion Magnetoresistance nanoscale effects Interfacial chemistry metal deposition metal dissolution nonlinear effects whisker growth Solid state kinetics Defect chemistry Solid state electrochemistry

7 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…)

8 Electrochemical surface control
T = 400 °C p(O2) = 10-5 mbar 350 µm 0 s 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

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

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

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

12 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 · 10-6 S/cm about 4 orders of magnitude conductivity reciprocal thickness ZrO2 (+ 12 mol% CaO) / Al2O3

13 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

14 Ion pumping into plasmas
At the end of my talk I will present one of our newest experimental ideas. We want to influence the plasma composition by using an ion-conducting reactor wall. In this case we are using the oxygen ion-conductor YSZ for manipulating a capacitively coupled oxygen discharge. The electrodes for the generation of the plasma are here. We have an additional electrode and a YSZ-sample in contact with the plasma. Now we are applying an additional electric potential. We have two possibilities. First, we can pump oxygen through the membrane into the plasma. Secondly, we can pump oxygen from the plasma to the outer side. In the literature we can find relatively new papers reporting on a comparable setup without a plasma. There are two japanese groups which build oxygen-ion sources by applying an electric field to an ion-conductor surface. They measured an emission of negative oxygen ions from the surface. If it would be possible to combine this experiment with an oxygen plasma, it may be possible to increase the negative ion density in the plasma.

15 Ion pumping into plasmas
Institut für Physik Universität Greifswald TALIF-Experiment Optisches System: - Nd:YAG gepumter Farbstofflaser (10 Hz / 355 nm) - Farbstoff : 1:1 Mischung Coumarin 47/ 120 - Filter : ( ) nm Parallelplattenentladung: - kapazitiv, asymmetrisch - f = 13,56 MHz max. Ueff ~ 600 V Arbeitsgas : Sauerstoff - p = Pa - Gasfluß = sccm Electrodes: - radius r = 40 mm, - distance d = 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

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

17 (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)

18 (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

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

20 (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)

21 24.06.2005 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

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