Spinodal decomposition is of great practical interest because it allows to obtain a finely dispersed microstructure, which in many cases makes it possible to significantly improve physical properties of materials. In particular, in modern chemistry of materials for the fabrication of multilayer thin-film systems, which are basic to most electrical, optical, biomedical, sensing, and many other functional devices, increasingly wide use is being made of self-organization through special thermodynamic conditions without resorting to complex or energy-consuming techniques. This review presents existing theories, experimental approaches and technologies of thin-film materials using analysis of the literature over the past 60 years with examples of decomposition of solid solutions in ceramics and glasses.

Epitaxial VO2 films on r-sapphire substrates with ideal composition, dense structure and superior functional properties were obtained by water-assisted MOCVD from vanadyl hexafluoroacetylacetonate followed by the annealing under optimized conditions. The obtained films exhibit both intense optical switch properties in IR region and unique MIT characteristics: change in resistance by 4.6 orders in the temperature range 40-80 degrees C, hysteresis width less 0.7 degrees C and transition width 1.5 degrees C. The proposed synthetic approach opens new opportunities to fabricate highly sensitive and ultrafast switches for optical, electronic and biomedical devices. (C) 2020 Elsevier B.V. All rights reserved.

We report a feasible and high-throughput method for high-quality W-doped VO2 nanostructured epitaxial films on r-sapphire substrate fabrication. Single-phase, smooth vanadium dioxide thin films with uniform distribution of tungsten (up to 2.3%) are formed using the solvothermal process from ethylene glycol/water V4+ and W6+ solutions. Compositional analysis by X-ray photoelectron and energy-dispersive X-ray spectroscopy (XPS and EDX, respectively); structural analysis (X-ray diffraction, Raman spectroscopy, selected area electron diffraction (SAED)); and detailed analysis of the surface morphology and substrate-film interface using scanning electron microscopy, atomic force microscopy, and high-resolution transmission electron microscopy (SEM, AFM, HRTEM, respectively) confirm the formation of nanoscale (50-60 nm) epitaxial W:VO2 (M-1) on r-sapphire with epitaxial relationships (100)VO2 parallel to(1012)Al2O3 and [010]VO2 parallel to[0110]Al2O3. The nanostructured films demonstrate excellent terahertz (THz) transmission properties: a phase transition temperature of 31 degrees C, a huge THz modulation depth of over 60%, and broad bandwidth (>= 2 THz) operation. Hence, they can be efficiently used as active material for tunable THz manipulation devices.

Titania mesocrystals were produced in the presence of polyethylene glycol 400. The doping of the mesocrystals with a small amount of vanadium was shown to increase the photocatalytic activity in comparison with undoped anatase mesocrystals. It was experimentally determined for the first time, using mild ultrasonication of the material, that the photocatalytic reaction of the decomposition of crystal violet occurs throughout the surface of the titania mesocrystals.

The present study reports the fast synthesis of VO2 (М1) oriented films on the r-Al2O3(012) substrates by the hydrothermal method using citric acid and vanadium (V) oxide as precursors with post deposition annealing in inert atmosphere. The effects of synthesis parameters (solution concentration and autoclave filling factor) on the films composition, morphology and electric properties are considered using XRD, Raman spectroscopy, AFM and SEM. The obtaining VO2(M1)/r-Al2O3 films show a metal-insulator transition with resistivity change of ~3.5 orders of magnitude and excellent thermochromic properties in the long-wavelength IR region. This work demonstrates a promising technique to promote the commercial implementation of VO2 as material for design of infrared (IR) switch devices.

Hydrothermal synthesis has been used to prepare textured Ti 1 – x V x O 2 coatings on the surface of r-Al 2 O 3 single-crystal substrates using ammonium hexafluorotitanate and vanadyl oxalate complex as precursors. The obtained samples have been characterized by X-ray diffraction, scanning electron microscopy, and X-ray spectral microanalysis.

The hydrothermal method is an effective approach for the synthesis of VO2 films with unique crystallites morphology and sharp electrical and optical switch properties.

Hydrothermal synthesis has been used to prepare textured Ti1– xVxO2 coatings on the surface of r-Al2O3 single-crystal substrates using ammonium hexafluorotitanate and vanadyl oxalate complex as precursors. The obtained samples have been characterized by X-ray diffraction, scanning electron microscopy, and X-ray spectral microanalysis.

hydrothermal synthesis of oriented six-pointed VO2(M1) caramboles

Temperature dependence of insulator-to-metal phase transition in VO2 epitaxial thin films was studied in the microwave range. Biaxially textured VO2 thin films were obtained on 3-inch sapphire substrates by the method of chemical vapour deposition (MCVD). The change in the electrical resistance with temperature reached approximately 3 orders of magnitude for the obtained films, measured in the metal-insulator phase transition region. Using a high-temperature quasi-optical setup, the microwave features of the phase transition in VO2 thin films were studied at temperature. The hysteresis of microwave properties of the studied samples was observed in the temperature range of VO2 phase transition.

In this paper, we propose a switchable focuser device based on a Fresnel zone plate (FZP) structure for terahertz (THz) applications. Each FZP contains seven rings, etched in thin VO2 film with the designed focal lengths of 50 and 100 mm for 3.7-THz frequency. Temperature-induced VO2 phase transition leads to the change in dielectric susceptibility of the material, which allows one to switch on and off the focusing properties of the device. The devices were tested with radiation of 3.1 and 3.7 THz emitted by quantum cascade lasers. Experimental results were compared with numerical simulations. In this article, we compare the FZP based on VO2 films with different properties and show that a thicker VO2 film reveals higher focusing efficiency, while a thinner one reveals a higher modulation ratio for the peak intensity at the focal point of FZP. We demonstrate experimentally the near-diffraction-limited size of the beam in the focal point of the device. Switching between two phase states of the VO2 films results in up to the 38-fold change of intensity in the focal point.

Superconducting wires are not perfectly homogeneous in term of critical current as well as stabilization. In resistive fault current limiter applications this could lead to hot spots if the fault current is only slightly above the nominal current of the device. Increasing stabilization by using thicker silver coating for example may prevent this problem but this method implies longer wire length to maintain the same impedance during a fault. Very efficient cooling in another way to prevent hot spots, this can be achieved in nucleate boiling regime. Optimal insulation can be used to prevent film boiling regime, staying in nucleate boiling regime in a much broader temperature range. In this work a novel technique is used to monitor in real time the temperature of the wire during the quench. Using this method several increasing insulation thicknesses are tested, measuring for each the heat exchange rate to the nitrogen bath. Exchange rate measurements are made in quasistatic regime and during the re-cooling of the wire. SuperOx wires provided with different insulation thicknesses exhibit an excellent stability, far above a bare wire. On the other side, for very thick insulations the stability gain is lost. Re-cooling speeds dependency on insulation thicknesses is measured too.

The crystal structures were determined for four novel and two earlier reported mixed ligand complexes of Ca, Sr and Ba hexafluoroacetylacetonates with two tetradentate polyglymes – triethyleneglycol dimethyl and monomethyl ethers (triglyme and trigmo respectively). The new compounds [M(hfa)2(trigmo)]2 have identical compositions and similar dimeric structures for M=Ca, Sr and Ba, while the volatile mixed ligand complexes with triglyme demonstrate a variety of compositions and structures depending on central ion. Among the Ba complexes, the novel volatile ionic supramolecular extraordinary crystal [Ba(hfa)(triglyme)2]2[Ba(hfa)4] was revealed. The thermal behavior in the gas phase for the full set of mixed ligand AEE hexafluoroacetylacetonates with tetraglyme, triglyme, trigmo and diglyme was discussed on the base of mass spectrometry and DFT calculations.