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Iridium-based oxides: Recent advances in coloration mechanism, structural and morphological characterization
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
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2008 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 92, no 2, 91-96 p.Article in journal (Refereed) Published
Abstract [en]

Films of iridium-tantalum oxide and iridium oxide have been prepared by sputtering and studied regarding their structure and electrochemical properties. X-ray diffraction and transmission electron microscopy showed an average grain size of 3-4 nm for both films. Point energy dispersive X-ray spectrometry showed an inhomogeneous distribution of iridium and tantalum indicating that the iridium-tantalum oxide may be a mixture of small IrO2 and Ta2O5 grains, which is consistent with the determined composition IrTa1.4O5.6. X-ray photoelectron spectroscopy gave valuable information on the stabilization process of the as-deposited films involving an uptake of oxygen, and on a coloration mechanism only including protons.

Place, publisher, year, edition, pages
2008. Vol. 92, no 2, 91-96 p.
National Category
Physical Sciences Engineering and Technology
URN: urn:nbn:se:uu:diva-96832DOI: 10.1016/j.solmat.2007.03.029ISI: 000251829800002OAI: oai:DiVA.org:uu-96832DiVA: diva2:171539
Available from: 2008-03-14 Created: 2008-03-14 Last updated: 2016-04-12Bibliographically approved
In thesis
1. Electrochromic Properties of Iridium Oxide Based Thin Films
Open this publication in new window or tab >>Electrochromic Properties of Iridium Oxide Based Thin Films
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electrochromic iridium oxide (IrOx) and iridium-tantalum oxide (IrTaOx) thin films were prepared by reactive magnetron sputtering. Composition, density, and structure were determined using Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy. The electronic density of states (DOS) and the solid phase chemical diffusion coefficient (D) were determined for hydrogen in IrOx and IrTaOx by potentiostatic intermittent titration technique (PITT), and electrochemical impedance spectroscopy (EIS). The complex refractive indices were determined for colored and bleached IrOx and IrTaOx by inverting transmission and reflectance, measured using spectrophotometry in the 300-2500 nm wavelength range.

A very porous structure, with a stoichiometry of IrO2.2, was found for IrOx. It contained ~4 nm sized grains. The IrTaOx had a denser structure built up by ~4 nm sized grains. The composition of IrTaOx was found to vary on a nanometer scale, with an average composition of IrTa1.4O5.6.

It was found that DOS can be measured using PITT and EIS in the presence of spontaneous side reactions, even for systems influenced by non-negligible charge transfer kinetics and Ohmic drops. It was found that the measured DOS is 30-50% of the theoretically calculated DOS and that D is in the 10-10 – 10-11 cm2/s range for both materials. The hydrogen diffusion mechanism was described by an anomalous diffusion model, possibly indicating percolation or diffusion paths described by a fractal network.

The refractive indices were found to be ~1.3 and ~2 for IrOx and IrTaOx, respectively, and independent of coloration state, whereas the extinction coefficients were found to modulate by ~30% for IrOx and ~50% for IrTaOx, making IrTaOx more favorable for electrochromic applications. A modulation peak was found at ~660 nm for both IrOx and IrTaOx associated with the removal of intraband transitions within the Ir t2g band.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 65 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 403
Engineering physics, Electrochromism, iridium oxide, hydrogen intercalation, chemical diffusion coefficient, density of states, optical modulation, Teknisk fysik
urn:nbn:se:uu:diva-8505 (URN)978-91-554-7116-3 (ISBN)
Public defence
2008-04-04, Häggsalen, The Ångström laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Available from: 2008-03-14 Created: 2008-03-14 Last updated: 2009-03-27Bibliographically approved

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Coronel, ErnestoNiklasson, Gunnar A.Granqvist, Claes-Göran
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