The O-V (Oxygen-Vanadium) system

Wriedt, H. A.

doi:10.1007/bf02877512

Cited by 139 publications

(68 citation statements)

References 45 publications

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“…The exposures were harsh, and 80-nm-thick VO 2 films rapidly converted to non-TC V 2 O 5 under the chosen conditions. The oxidation mechanism may be inferred, schematically, from the equilibrium phase diagram of the oxygen-vanadium system [19,20]. Thus tetragonal VO 2 (β-phase, space group P4 2 /mnm, at τ > 68 °C ) is expected to transform progressively into monoclinic V 6 O 13 (C2/m at τ > -124 °C) and V 3 O 7 (C2/c) until ultimately reaching orthorhombic V 2 O 5 (Pmnm).…”

Section: Conclusion and Remarksmentioning

confidence: 99%

“…However, there has been substantial progress towards the alleviation of all of these obstacles, and it is well known that tungsten doping can decrease τ c to room temperature [11,12], that luminous absorptance can be lowered by magnesium doping [13][14][15][16], and that solar energy modulation can be boosted by invoking VO 2 -based nanoparticles rather than thin films [16][17][18]. Another obvious requirement for practical implementation of TC VO 2 -based films and nanoparticles is that they must maintain their desirable properties during extended periods of time, which is far from obvious since V 2 O 5 , not VO 2 , is the thermodynamically stable oxide [19,20].…”

Section: Introductionmentioning

confidence: 99%

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Durability of thermochromic VO2 thin films under heating and humidity: Effect of Al oxide top coatings

Niklasson

et al. 2014

Thin Solid Films

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An explorative study was performed on sputter-deposited thermochromic (TC) VO 2 films exposed to heat treatment under dry and humid conditions. The ambient conditions were harsh and 80-nm-thick VO 2 films rapidly converted to non-TC V 2 O 5 . It was found that a 30-nm-thick sputter-deposited Al oxide top coating provided good protection and delayed the oxidation for more than one day upon heating in dry air at 300 °C and that protection occurred for several days at 95 % relative humidity and 60 °C. The thickness of the Al oxide was important and, expectedly, increased thickness yielded enhanced protection. Our results are important for TC fenestration as well as for other technical applications.

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Section: Conclusion and Remarksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Durability of thermochromic VO2 thin films under heating and humidity: Effect of Al oxide top coatings

Niklasson

et al. 2014

Thin Solid Films

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“…While some perovskite oxides retain their phase irrespective of huge P(O 2 ) variation, 22,23 it is quite expectable that the phases of vanadium oxides are very sensitive to a slight change in P(O 2 ) since the equilibrium solid-phase diagram for the V-O system is quite complex. 24 Here, we report the growth control of the valence state in vanadium oxides by systematically controlling P(O 2 ) during pulsed laser deposition, followed subsequently by postannealing under highly oxidizing conditions. We found that the room temperature MIT could be 5 observed only in VO 2 thin films grown in a very narrow window of P(O 2 ).…”

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confidence: 99%

Growth control of the oxidation state in vanadium oxide thin films

Lee

Meyer

Park

et al. 2014

Applied Physics Letters

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Precise control of the chemical valence or oxidation state of vanadium in vanadium oxide thin films is highly desirable for not only fundamental research, but also technological applications that utilize the subtle change in the physical properties originating from the metalinsulator transition (MIT) near room temperature. However, due to the multivalent nature of vanadium and the lack of a good understanding on growth control of the oxidation state, stabilization of phase pure vanadium oxides with a single oxidation state is extremely challenging. Here, we systematically varied the growth conditions to clearly map out the growth window for preparing phase pure epitaxial vanadium oxides by pulsed laser deposition for providing a guideline to grow high quality thin films with well-defined oxidation states ofA well pronounced MIT was only observed in VO 2 films grown in a very narrow range of oxygen partial pressure P(O 2 ). The films grown either in lower (< 10 mTorr) or higher P(O 2 ) (> 25 mTorr) result in V 2 O 3 and V 2 O 5 phases, respectively, thereby suppressing the MIT for both cases. We have also found that the resistivity ratio before and after the MIT of VO 2 thin films can be further enhanced by one order of magnitude when the films are further oxidized by post-annealing at a well-controlled oxidizing ambient. This result indicates that stabilizing vanadium into a single valence state has to compromise with insufficient oxidation of an as grown thin film and, thereby, a subsequent oxidation is required for an 3 improved MIT behavior. TextVanadium oxides are one of few binary oxides exhibiting intriguing strong correlation effects that are critically dependent upon the oxidation state of vanadium. . [6][7][8][9] In particular, the MIT near room temperature makes this phase most attractive. (3) V 2 O 5 (3d 0 , V +5 ) that is an insulator and has an orthorhombic layered structure (a = 11.54 Å, b = 3.57 Å, c = 4.38 Å). Its structure makes it attractive for electrode applications in, e.g., Li-ion batteries 10,11 and actuators. 12 As was found for perovskite oxides, [13][14][15] it is tempting to consider these vanadium oxides as oxygen sponges, by which one can obtain a strong contrast in the physical properties by reversibly transitioning between the phases. Moreover, the redox process Here, we report the growth control of the valence state in vanadium oxides by systematically controlling P(O 2 ) during pulsed laser deposition, followed subsequently by postannealing under highly oxidizing conditions. We found that the room temperature MIT could be 5 observed only in VO 2 thin films grown in a very narrow window of P(O 2 ). Moreover, interestingly, the MIT behavior could be further enhanced by post-annealing in high-pressure oxygen, implying that the optimal growth pressure to obtain phase pure films with high crystallinity was not enough to fully oxidize the films. This result ultimately stresses the importance of oxygen content in VO 2 that plays a critical role in the sharpness and resistivity r...

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“…Vanadium has high oxygen affinity and is able to form compounds with the metal in oxidation states being +5, +4, +3 and +2. Therefore, it is hardly surprising that the vanadium-oxygen phase diagram, shown in Figure 4, is complex and includes almost 20 different phases, frequently with only minor compositional differences [55][56][57][58]. The challenges for the synthesis of VO2 are related to the co-existence of these various oxide forms and also with the existence of various polymorphs.…”

Section: On the Preparation Of Vanadium Dioxide (Vo2) Thin Films And mentioning

confidence: 99%

Thermochromic Oxide-Based Thin Films and Nanoparticle Composites for Energy-Efficient Glazings

Granqvist

Niklasson

2016

Buildings

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Today's advances in materials science and technology can lead to better buildings with improved energy efficiency and indoor conditions. Particular attention should be directed towards windows and glass facades-jointly known as "glazings"-since current practices often lead to huge energy expenditures related to excessive inflow or outflow of energy which need to be balanced by energy-intensive cooling or heating. This review article outlines recent progress in thermochromics, i.e., it deals with materials whose optical properties are strongly dependent on temperature. In particular, we discuss oxide-based thin surface coatings (thin films) and nanoparticle composites which can be deposited onto glass and are able to regulate the throughput of solar energy while the luminous (visible) properties remain more or less unaltered. Another implementation embodies lamination materials incorporating thermochromic (TC) nanoparticles. The thin films and nanocomposites are based on vanadium dioxide (VO 2 ), which is able to change its properties within a narrow temperature range in the vicinity of room temperature and either reflects or absorbs infrared light at elevated temperatures, whereas the reflectance or absorptance is much smaller at lower temperatures. The review outlines the state of the art for these thin films and nanocomposites with particular attention to recent developments that have taken place in laboratories worldwide. Specifically, we first set the scene by discussing environmental challenges and their relationship with TC glazings. Then enters VO 2 and we present its key properties in thin-film form and as nanoparticles. The next part of the article gives perspectives on the manufacturing of these films and particles. We point out that the properties of pure VO 2 may not be fully adequate for buildings and we elaborate how additives, antireflection layers, nanostructuring and protective over-coatings can be employed to yield improved performance and durability that make TC glazings of considerable interest for building-related applications. Finally, we briefly describe recent developments towards TC light scattering and draw some final conclusions.

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The O-V (Oxygen-Vanadium) system

Cited by 139 publications

References 45 publications

Durability of thermochromic VO2 thin films under heating and humidity: Effect of Al oxide top coatings

Durability of thermochromic VO2 thin films under heating and humidity: Effect of Al oxide top coatings

Growth control of the oxidation state in vanadium oxide thin films

Thermochromic Oxide-Based Thin Films and Nanoparticle Composites for Energy-Efficient Glazings

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