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Polyoxoniobates as molecular building blocks in thin films
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0003-1054-221x
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0002-2298-8844
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0003-3927-6197
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0002-3804-6421
2021 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 50, no 44, p. 16030-16038Article in journal (Refereed) Published
Abstract [en]

Niobium oxide thin films have been prepared by spin-coating aqueous solutions of tetramethylammonium salts of the isostructural polyoxometalate clusters [Nb10O28]6−, [TiNb9O28]7− and [Ti2Nb8O28]8− onto silicon wafers, and annealing them. The [Nb10O28]6− cluster yields films of Nb2O5 in the orthorhombic and monoclinic crystal phases when annealed at 800 °C and 1000 °C, respectively, whereas the [TiNb9O28]7− and [Ti2Nb8O28]8− clusters yield the monoclinic crystal phases of Ti2Nb12O29 and TiNb2O7 (titanium–niobium oxides) in different ratios. We also demonstrate a protocol for depositing successive layers of metal oxide films. Finally, we explore factors affecting the roughness of the films.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2021. Vol. 50, no 44, p. 16030-16038
National Category
Inorganic Chemistry
Research subject
Materials Science; Inorganic Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-188370DOI: 10.1039/D1DT03116CISI: 000704490900001PubMedID: 34613326Scopus ID: 2-s2.0-85119868258OAI: oai:DiVA.org:umu-188370DiVA, id: diva2:1601109
Available from: 2021-10-06 Created: 2021-10-06 Last updated: 2022-08-25Bibliographically approved
In thesis
1. Tunable surfaces: using polyoxoniobates and -tantalates as molecular building blocks
Open this publication in new window or tab >>Tunable surfaces: using polyoxoniobates and -tantalates as molecular building blocks
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Avstämbara ytor : användning av polyoxoniobater och -tantalater som molekylära byggstenar
Abstract [en]

This thesis describes and explains the use of aqueous polyoxometalates (POMs), as molecular building blocks in the fabrication of tunable solid-state materials, such as thin films.  Microwave irradiation in the synthesis of Nb10, Nb6 and Ta6 is a rapid and efficient alternative to conventional hydrothermal methods, while offering equal – if not greater yields – of product. Through microwave irradiation, the concept of an activation pH of anhydrous Nb2O5, niobic and tantalic acids has been devised to explain what products are accessible from each oxide and under what conditions.

The controlled deposition of metal oxide thin films is possible via an iterative spin coating and annealing process of POMs. This approach facilitates deposition of alkali-free, metal oxide thin films with varying crystallinity, thickness and roughness. The ability to deposit successive layers of these polyoxometalate films was a new approach to create thicker and layered metal oxide films. This approach offers an efficient and reproducible means of creating tunable metal oxide thin films or other solid-state structures, which exemplifies the use of POMs as molecular building blocks.

Transition metal niobate thin films can be deposited onto silicon wafers via the aqueous deposition of transition metal-hexaniobate mixtures. This facilitates assessment of the electrochemical properties of these materials, without a need for coin cells or inert conditions. This allows for characterisation of the pseudocapacitive properties of these materials, which abodes well for developing electrochemical energy storage devices.

The viability of using aqueous polyoxoniobate-alkali nitrate mixtures was leveraged as a means of depositing alkali niobate (LiNbO3, NaNbO3, KNbO3) thin films, plus Rb and Cs doped Nb2O5 films and powders. Synthesising solid-state niobates that can incorporate all the alkali cations, entirely from aqueous polyoxoniobate solutions, confers the ability to develop lead-free piezoelectric, ferroelectric and antiferroelectric materials without the use of expensive or energy intensive methods.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2022. p. 224
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-198826 (URN)978-91-7855-850-6 (ISBN)978-91-7855-851-3 (ISBN)
Public defence
2022-09-23, Lilla Hörsalen, Department of Chemistry, KBC-Building, Umeå, 10:15 (English)
Opponent
Supervisors
Available from: 2022-09-02 Created: 2022-08-24 Last updated: 2022-09-02Bibliographically approved

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Rambaran, MarkGorzsás, AndrásHolmboe, MichaelOhlin, C. André

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