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Electrochromic Nickel – Tungsten Oxides: Optical, Electrochemical and Structural Characterization of Sputter-deposited Thin Films in the Whole Composition Range
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates the electrochromic NixW1-x oxide thin film system, where 0 < x < 1. The thin films were deposited by reactive DC magnetron co-sputtering from one Ni and one W metal target. In addition, Ni oxide was deposited with water vapor added to the sputtering gas. The different compositions were structurally characterized by X-ray diffraction, X-ray photoelectron-, Rutherford backscattering- and Raman spectroscopy. Possible nanostructures were studied by ellipsometry together with effective medium theory. Optical and electrochemical properties were investigated by spectrophotometry and cyclic voltammetry in 1 M lithium perchlorate in propylene carbonate (Li-PC). Li-PC electrolyte was used as it is being compatible with both W and Ni oxides. Few studies have previously been made on Ni oxides in Li-PC.

Films with high Ni content, 0.85 < x < 1, were polycrystalline and all other films were amorphous. W-rich films, x < 0.5, consisted of a mixture of W oxide and NiWO4 -phases, and the Ni-rich samples, x > 0.5, probably consisted of hydrated Ni oxide and NiWO4 -phases. Films with 0 < x < 0.3 showed electrochromic properties similar to W oxide, and films with 0.7 < x < 1 behaved as Ni oxide. For 0.4 < x < 0.7 no optical change was seen. At the border of cathodic electrochromic and non-electrochromic behavior, i.e. x ~ 0.4, the sample behaved as an optically passive intercalation material. The transmittance change was 0.45 and 0.15 for the W-rich and Ni-rich films, respectively. Ni addition to W oxide improved the coloration efficiency. For the Ni-rich films the charge insertion/extraction and optical modulation was low and an aging effect resulted in strong bleaching of the samples. The advantage of W addition to Ni oxide was that the transparency at the bleached state was enhanced. Moreover, it was found that the hydrous character of the Ni oxide had a large impact on the electrochromic performance, both when electrochemically cycled in KOH and in the non-aqueous Li-PC.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , 116 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 963
Keyword [en]
Electrochromism, Nickel oxide, Tungsten oxide, Lithium intercalation, Sputtering, Thin films, Nanostructures, Optical properties
National Category
Materials Engineering
Research subject
Solid State Physics
Identifiers
URN: urn:nbn:se:uu:diva-179764ISBN: 978-91-554-8444-6 (print)OAI: oai:DiVA.org:uu-179764DiVA: diva2:546180
Public defence
2012-10-12, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2012-09-21 Created: 2012-08-22 Last updated: 2013-01-22Bibliographically approved
List of papers
1. Electrochromism in Nickel Oxide and Tungsten Oxide Thin Films: Ion Intercalation from Different Electrolytes
Open this publication in new window or tab >>Electrochromism in Nickel Oxide and Tungsten Oxide Thin Films: Ion Intercalation from Different Electrolytes
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2009 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 93, no 12, 2050-2055 p.Article in journal (Refereed) Published
Abstract [en]

Electrochromic (EC) NiOz and WOy thin films were prepared by sputtering   and were used in a feasibility study aimed at investigating mixtures of   these two oxides. The object was to identify a suitable electrolyte,   compatible with both NiOz and WOy. To that end we carried out cyclic   voltammetry (CV) in potassium hydroxide (KOH), propionic acid, and   lithium perchlorate in propylene carbonate (Li-PC). WOy could be   coloured in propionic acid and Li-PC, while NiOz could be coloured only   in KOH. Both films showed best stability in Li-PC, which hence is well   suited for further studies of mixed NiOz and WOy.

Keyword
Electrochromism, Nickel oxide, Tungsten oxide, Cyclic voltammetry, Spectrophotometry
National Category
Physical Sciences Engineering and Technology
Research subject
Solid State Physics
Identifiers
urn:nbn:se:uu:diva-122131 (URN)10.1016/j.solmat.2009.05.009 (DOI)000271792200005 ()
Available from: 2011-09-21 Created: 2010-04-06 Last updated: 2017-12-12Bibliographically approved
2. Structure and composition of sputter-deposited nickel-tungsten oxide films
Open this publication in new window or tab >>Structure and composition of sputter-deposited nickel-tungsten oxide films
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2011 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 7, 2062-2066 p.Article in journal (Refereed) Published
Abstract [en]

Films of mixed nickel-tungsten oxide, denoted NixW1−x oxide, were prepared by reactive DC magnetron cosputtering from metallic targets and were characterized by Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffractometry and Raman spectroscopy. A consistent picture of the structure and composition emerged, and at x<0.50 the films comprised a mixture of amorphous WO3 and nanosized NiWO4, at x=0.50 the nanosized NiWO4 phase was dominating, and at x>0.50 the films contained nanosized NiO and NiWO4.

National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-178364 (URN)10.1016/j.tsf.2010.10.033 (DOI)
Available from: 2012-07-31 Created: 2012-07-31 Last updated: 2017-12-07Bibliographically approved
3. Ellipsometrically determined optical properties of nickel-containing tungsten oxide thin films: Nanostructure inferred from effective medium theory
Open this publication in new window or tab >>Ellipsometrically determined optical properties of nickel-containing tungsten oxide thin films: Nanostructure inferred from effective medium theory
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2012 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 4, 044308- p.Article in journal (Refereed) Published
Abstract [en]

Films of NixW1−x oxide with 0.05 ≤ x ≤ 0.53 were produced by reactive dc magnetron co-sputtering onto Si. Such films have documented electrochromism. Spectroscopic ellipsometry was used to extract accurate data on the dielectric function in the photon range 0.062 to 5.62 eV. The results for 0.62 to 5.62 eV were compared with computations from the Bruggeman effective medium theory applied to two nanostructural models: one representing a random mixture of structural entities characterized by the dielectric functions of WO3 and NiWO4 and the other describing a random mixture of WO3 and NiO. Unambiguous evidence was found in favor of the former model, and hence the films are composed of nanosized tungsten oxide and nickel tungstate. This agrees excellently with an earlier investigation of ours on NixW1−x oxide films, where nanostructure was inferred from Raman spectroscopy, x-ray photoelectron spectroscopy, and x-ray diffraction.

National Category
Materials Engineering
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-179762 (URN)10.1063/1.4748166 (DOI)000308410100079 ()
Available from: 2012-08-22 Created: 2012-08-22 Last updated: 2017-12-07Bibliographically approved
4. Electrochromism in sputter deposited nickel-containing tungsten oxide films
Open this publication in new window or tab >>Electrochromism in sputter deposited nickel-containing tungsten oxide films
2012 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 99, 339-344 p.Article in journal (Refereed) Published
Abstract [en]

Thin films of NixW1-x oxide were prepared by reactive DC magnetron co-sputtering and were investigated by optical and electrochemical measurements. Electrochromism was found only for 0<x<0.3 but not for 0.3<x<0.6, though films with x~0.4 could still sustain reversible charge insertion. The coloration efficiency was largest for 0.10<x<0.15. The charge capacity of the NixW1-x oxide films decreased upon increasing the value of x as a consequence of a decreasing ion diffusion coefficient leading to slower kinetics.

National Category
Materials Engineering
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-178580 (URN)10.1016/j.solmat.2011.12.025 (DOI)000301167200048 ()
Funder
Swedish Research CouncilEU, FP7, Seventh Framework Programme, 211948Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning
Available from: 2012-07-31 Created: 2012-07-31 Last updated: 2017-12-07Bibliographically approved
5. Structure and optical properties of electrochromic tungsten-containing nickel oxide films
Open this publication in new window or tab >>Structure and optical properties of electrochromic tungsten-containing nickel oxide films
2014 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 126, 248-259 p.Article in journal (Refereed) Published
Abstract [en]

Electrochromic NixW1-x oxide thin films with 0.5 < x < 1, were deposited by co-sputtering from one Ni and one W metal target. The different compositions were structurally characterized by X-ray diffraction, X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. The optical and electrochemical properties were investigated by spectrophotometry and cyclic voltammetry in LiClO4 dissolved in propylene carbonate. It was found that the samples turned amorphous upon W addition and that the NixW1-x oxides probably consisted of hydrated Ni oxides and NiWO4. The charge insertion/extraction and optical modulation was unfortunately very modest. Moreover, an aging effect, resulting in a strong bleaching process of the samples was observed. Nevertheless, it was found that, for electrochromic applications, the advantage of W addition was that the transparency at the bleached state was enhanced for all compositions and for wavelengths of 400 nm up to NIR.

National Category
Materials Engineering
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-179763 (URN)10.1016/j.solmat.2013.04.001 (DOI)000338395100036 ()
Conference
10th International Meeting on Electrochromism (IME), Holland, MI, August 12-16, 2012
Available from: 2012-08-22 Created: 2012-08-22 Last updated: 2017-12-07Bibliographically approved
6. Electrochromic properties of nickel oxide based thin films sputter deposited in the presence of water vapor
Open this publication in new window or tab >>Electrochromic properties of nickel oxide based thin films sputter deposited in the presence of water vapor
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2012 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 10, 3839-3842 p.Article in journal (Refereed) Published
Abstract [en]

Electrochromic nickel oxide based thin films were prepared by reactive RF magnetron sputtering from metallic nickel in the presence of Ar, O-2 and H2O. The water vapor led to enhanced optical modulation and charge capacity. At a wavelength of 550 nm the bleached state transmittance was 0.73 and the transmittance for the colored state was 0.28 and 0.15 for water partial pressures of p(H2O)<10(-3) Pa and p(H2O) similar to 7 x 10(-2) Pa, respectively. The charge densities were 14 and 25 mC/cm(2) for p(H2O)<10(-3) Pa and P-H2O similar to 7 x 10(-2) Pa, respectively. The coloration efficiency was decreased with increased water partial pressure, from about 0.07 to 0.06 cm(2)/mC. Preliminary results show that the H2O promotes an amorphous structure and makes the films increasingly hydrous. 

Keyword
Nickel oxide, Electrochromism, RF magnetron sputtering, Water vapor, Thin film, Optical properties, Charge capacity
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-174595 (URN)10.1016/j.tsf.2011.08.030 (DOI)000302973400027 ()
Available from: 2012-05-24 Created: 2012-05-22 Last updated: 2017-12-07Bibliographically approved

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