Papers by Keyword: Vanadium Dioxide

Abstract: A significant influence of temperature width found on the vanadium oxide properties, it plays a major role in highlighting the thermal limits of the three phases (metallic, semiconductor, and dielectric). Two values of the temperature width , and , had taken and studied their effect on both the dielectric constant and its two parts; refractive index, and extinction coefficient, and. It found that: as the temperature width is greater, the more the properties of the three phases for . In addition to increasing the thermal range for phases which can be reached to when , while it's at . Our results have achieved great compatibility with the published results globally. In addition to the effect of both ultraviolet, visible, and infrared radiation on vanadium oxide, according to the different phases of the metal, semiconductor, and dielectric, where the behavior of any of them differs according to the effect of the radiation affecting it. It is noted that the behavior is almost identical to both the extinction coefficient, and refractive at the visible region, on the contrary other two regions where the behavior of the three phases is evident in it.

Abstract: Vanadium oxide films have been fabricated by the acetylacetonate and triethoxy vanadyl sol-gel methods on silicon substrates, as well as by magnetron sputtering on glass-ceramic substrates. Additional annealing in reducing atmosphere results in formation of vanadium dioxide or mixed phases with a VO₂ predominance. The obtained films demonstrate the metal-insulator transition and electrical switching. In the films produced from triethoxy vanadyl, the peculiarities of electrical properties are related to the size effect, heterophase character of vanadium oxide films, and different types of charge carriers in the bulk of nanocrystallites and on their surfaces. Also, the effect of doping with hydrogen by means of plasma-immersion ion implantation on the properties of vanadium dioxide is explored. It is shown that the transition parameters in VO₂ thin films depend on the hydrogen implantation dose. At doses exceeding a certain threshold value, the films are metallized, and the phase transition no longer occurs.

Abstract: Mo-doped vanadium dioxide particles were produced by simple solution-based, rapid microwave assisted, and calcination in an inert gas method respectively. The precursors and the heat-treated final powders were characterized by X-ray diffractometer (XRD), differential scanning calorimeter (DSC), scanning electron microscope (SEM), and transmission electron microscope (TEM). The Mo dopant influenced the crystal structure and phase transition of VO₂ (M) particles. The XRD pattern indicated that all Mo-doped VO₂ particles were monoclinic crystal. The DSC results showed that phase transformation temperature of VO₂ from monoclinic to tetragonal or rutile, which normally occurred at 67-68 oC was reduced to 43.18 oC, whereas over doping of Mo led to the increased transition temperature. The results suggested a significant effect of Mo doping content on the transition temperature of VO₂. Doping with an optimum amount of Mo into VO₂ structure can achieve the lowest phase transformation temperature of VO₂ powders.

Abstract: Thermochromic nano-pigments of ZnO and WO₃ co-doped VO₂ for mixing in paint were prepared by chemical method. The samples were successfully synthesized after annealing at 700°C for 1 h in nitrogen atmosphere. ZnO concentrations of 0.1, 0.3 and 0.5 at% were co-doped with WO₃ in VO₂. The 0.1 at% ZnO doping exhibited an amorphous phase, while 0.3 and 0.5 at% ZnO doping showed monoclinic phase having thermochromic transition temperatures of 59.43 and 52.60°C, respectively. The crystallite size of 0.5 at% ZnO doped monoclinic phase was 42 nm. The coating paints on glass substrates were prepared by mixing white colour paint with 0.1, 0.3 and 0.5 wt% of the 0.5 at% ZnO and WO₃ co-doped VO₂ nano-pigment. It was found that the paint with 0.5 wt% loading exhibited self-cleaning properties and 99.99% antibacterial against under UV irradiation for 40 min.

Abstract: The exploration of efficient preparation methods of VO₂(M) powders, especially the controls of particle sizes, is a challenge. In this article VO₂(M) powders were prepared by a liquid phase precipitation and post annealing method. The structure and morphology of the VO₂(M) powders were characterized by XRD and SEM. The effects of annealing temperature and the amounts of additive SiO₂ aerogels on the particle size controlling were studied .The thermal phase transition properties were characterized by DSC analysis. The results reveal that the transformation of crystal phases from V₆O₁₃ to VO₂(M) takes place in the annealing process and the additive of SiO₂ aerogels can control the particle size and promote the particle size to be smaller effectively.

Abstract: Vanadium dioxide (VO₂) has attracted much interest in material field due to its unique semiconductor-metal phase transition properties. And now, the problem of stability has been highlighted and concerned for the practical application in VO₂. In order to establish a relatively complete guide of stability study on VO₂ which would contribute to deeply and systematically researches, the article made a review of the stability study on VO2 from thermal excitation, photo-excitation and electro-excitation. Moreover, the key aspects for future research on the stability study of VO₂ was proposed.

Abstract: A new process was developed for synthesizing tungsten-doped vanadium dioxide VO₂(M) from ammonium metavanadate. The process includes obtaining V₂O₅ by pyrolysing NH₄VO₃, doping tungsten in V₂O₅ by sol-gel method, and reducing V₂O₅ to VO₂(M) with hydrazine by hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were applied to characterizing the product. The experimental results indicated that tungsten doped VO₂ (M) nanoparticles were successfully synthesized. The product VO₂ (M) presents mainly rod-like and block-like morphology. The phase transition temperature decreases with tungsten doped amount increasing, the phase transition takes place over the range from 36.23°C to 62.16°C and the largest enthalpy of the phase transition is 16.24J/g.

Abstract: Vanadium dioxide (VO₂) films were grown on c-and m-plane sapphire substrates by pulsed laser deposition (PLD) technique with VO₂ ceramic target. The VO₂ films with preferred growth orientation and uniform dense distribution have been achieved on both substrates, as confirmed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The terahertz (THz) transmission properties of VO₂ thin films were studied by terahertz time-domain spectroscopy (THz-TDS). The results indicate that the THz transmission properties of VO₂ films are strongly influenced by the sapphire substrate orientation, suggesting that VO₂ films are ideal material candidates for THz modulation.

Abstract: The VO₂ thin film is a kind of functional material with phase transition properties, and has broad application prospects. In this paper, the main VO₂ thin film preparation methods of sputtering, chemical vapor deposition, sol-gel method and the research status of electrical properties, optical properties , phase change properties and the calculation theory study were summarized. The main application fields and application progress of the VO₂ thin films in the smart windows, the infrared pulse laser protective films, the photonic crystal, the dielectric material of CD, the material of optical and electrical switch were introduced.

Abstract: Optical properties of thin films of vanadium thermally oxidized at air were studied by ellipsometric method using wavelength of He-Ne laser. Multipart composition of these films was revealed and method of optimization of technological conditions based on dynamic of changing optical constants near 68°C was developed.