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surface:research:zirconia [2014-06-30 09:46]
surface:research:zirconia [2014-06-30 09:52] (current)
Michael Schmid subscripts fixed
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 +====== Zirconia – In Your Mouth and Your Car? ======
 +Zirconia (ZrO<sub>2</sub>) is one of the most common ceramic materials. Zirconia is used in engineering and in dentistry (tooth crowns), and it has a unique property that makes it ideal for many applications: At high temperatures, doped zirconia is a good conductor for oxygen ions, but it remains an insulator for electrons. Thus, any electric current through zirconia means oxygen transport, and oxygen transport is accompanied by a an electric current and voltage. Therefore, zirconia is used for [[wp>Solid oxide fuel cell|solid oxide fuel cells]] and oxygen sensors (e.g., [[wp>Lambda_sensor|lambda sensor]] for exhaust gas of cars).
 +
 +{{ :surface:research:zro2_on_pt3zr.jpg?200|Ultrathin ZrO2 film on Pt3Zr}}
 +Having a perfect insulator for electrons (but an ionic conductor) is a blessing for applications, but a curse if we want to study its surface by scanning tunneling microscopy (STM) or many other techniques. The way out is studying very thin zirconia films on metals; such films are still sufficiently conductive for STM. We have developed a technique to create well-ordered ultrathin ZrO<sub>2</sub> films by oxidation of alloys containing Zr, Pt<sub>3</sub>Zr or Pd<sub>3</sub>Zr. These ZrO<sub>2</sub> films are very thin indeed, they consist only of two oxygen layers and one Zr layer in between! Nevertheless, they are very similar to the "real" material, thick (bulk) ZrO<sub>2</sub>: Their structure is essentially the same, and both possess a similar [[wp>Band gap|band gap]].
 +
 +STM shows us the Zr atoms, perfectly well ordered on this surface. Density functional theory calculations (done in the Computational Materials Science group at our institute) tell us how the film binds to the substrate and much more.
 +
 +Recently, we have found that water bonding at these surfaces (both ultrathin films and "thick" ZrO<sub>2</sub>) is unusually strong for such an oxide. While we nicely see the H<sub>2</sub>O molecules by STM, they are almost hidden for some spectroscopy techniques that are usually applied to detect adsorbed water! Read more about this in a while...
 +
 +===== References =====
 +
 +
 +  - **Pt<sub>3</sub>Zr(0001): A substrate for growing well-ordered ultrathin zirconia films by oxidation**\\ M. Antlanger, W. Mayr-Schmölzer, J. Pavelec, F. Mittendorfer, J. Redinger, P. Varga, U. Diebold, and M. Schmid\\ [[doi>10.1103/PhysRevB.86.035451|Phys. Rev. B 86, 035451 (2012)]] ⋅ {{http://www.iap.tuwien.ac.at/www-surface/pdf/A/A2012E10.pdf|full text}}
 +  - **The growth of ultra-thin zirconia films on Pd<sub>3</sub>Zr(0001)**\\ J. I. J. Choi, W. Mayr-Schmölzer, F. Mittendorfer, J. Redinger, U. Diebold, and M. Schmid\\ [[doi>10.1088/0953-8984/26/22/225003|J. Phys.: Condens. Matter 26, 225003 (2014)]] ⋅ {{http://www.iap.tuwien.ac.at/www-surface/pdf/F/A2014E05.pdf|full text}}
 +
 +<small>The zirconia project was financed by the Austrian Science Fund as part of the [[http://foxsi.tuwien.ac.at/|SFB Functional Oxide Surfaces and Interfaces]]</small>