Troy D. Manning

Intelligent window coatings: atmospheric pressure chemical vapour deposition of vanadium oxides

Thin films of the vanadium oxides, V2O5, VO2, VOx (x = 2.00–2.50) and V6O13 were prepared on glass substrates by atmospheric pressure chemical vapour deposition (APCVD) of vanadium tetrachloride and water at 400–550 °C. The specific phase deposited was found to be dependent on the substrate temperature and the reagent concentrations. The films were characterised by Raman microscopy, X-ray diffraction (XRD), Rutherford backscattering (RBS), scanning electron microscopy (SEM), energy dispersive analysis by X-rays (EDX), reflectance/transmittance and UV absorption spectroscopy. The VO2 films show by Raman microscopy and reflectance/transmittance spectroscopy, reversible switching behaviour at 68 °C associated with a phase change from monoclinic (MoO2 structure) to tetragonal (TiO2, rutile structure).

Atmospheric pressure chemical vapour deposition of tungsten doped vanadium(IV) oxide from VOCl3, water and WCl6

Thin films of thermochromic tungsten doped VO2 on glass substrates were prepared from the atmospheric pressure chemical vapour deposition (APCVD) reaction of VOCl3,·H2O and WCl6. X-Ray diffraction (XRD) and Raman spectroscopy indicated a solid solution V1−xWxO2 (x = 0.003–0.032). XPS studies indicated the tungsten was present as W4+. The thermochromic properties of the films were investigated by Raman, XRD and reflectance/transmission measurements. These indicated that incorporation of tungsten caused a reduction in the VO2 thermochromic switching temperature of 19 °C per W atom%. The thermochromic properties of the thin films show great potential for use as an intelligent window coating.

APCVD of thermochromic vanadium dioxide thin films—solid solutions V2−xMxO2 (M = Mo, Nb) or composites VO2 : SnO2

Atmospheric pressure chemical vapour deposition of V2−xMxO2 (M = Mo, Nb; X = 0.01–0.003) thin films was achieved on glass substrates from the reaction of VOCl3, H2O and MCl5. Comparable reactions with SnCl4 formed SnO2 : VO2 composites. The ease with which solid solutions or composite films formed was related to the relative reaction rates. The films were characterised by X-ray diffraction, Raman, X-ray photoelectron spectroscopy and scanning electron microscopy. Doping of the VO2 phase was shown to affect both the growth morphology and the thermochromic properties of the films. The Mo-doped VO2 films showed a thermochromic switch of 47 °C with a narrow hysteresis (4–6 °C).

Improved electrical mobility in highly epitaxial La:BaSnO3 films on SmScO3(110) substrates

Heteroepitaxial growth of BaSnO3 and Ba1−xLaxSnO3 (x = 7%) lanthanum doped barium stannate thin films on different perovskite single crystal (SrTiO3 (001) and SmScO3 (110)) substrates has been achieved by pulsed laser deposition under optimized deposition conditions. X-ray diffraction measurements indicate that the films on either of these substrates are relaxed due to the large mismatch and present a high degree of crystallinity with narrow rocking curves and smooth surface morphology while analytical quantification by proton induced X-ray emission confirms the stoichiometric La transfer from a polyphasic target, producing films with measured La contents above the bulk solubility limit. The films show degenerate semiconducting behavior on both substrates, with the observed room temperature resistivities, Hall mobilities, and carrier concentrations of 4.4 mΩ cm, 10.11 cm2 V−1 s−1, and 1.38 × 1020 cm−3 on SmScO3 and 7.8 mΩ cm, 5.8 cm2 V−1 s−1, and 1.36 × 1020 cm−3 on SrTiO3 ruling out any extrinsic contribution from the substrate. The superior electrical properties observed on the SmScO3 substrate are attributed to reduction in dislocation density from the lower lattice mismatch.

Atmospheric pressure chemical vapour deposition of VO2 and VO2/TiO2 films from the reaction of VOCl3, TiCl4 and water

Vanadium dioxide films were deposited on glass from the APCVD reaction of VOCl3 and water at 650 degreesC. Introduction of a second precursor TiCl4 affected the growth morphology of the VO2 films but did not incorporate any detectable titanium. The films were characterised by XPS, XRD, Raman, EDAX and SEM. Interestingly the VO2 films formed in the presence of TiCl4 showed a reduction in the thermochromic switching temperature from 69 degreesC in bulk VO2 to 49 degreesC. APCVD of TiCl4/ VOCl3 at a substrate temperature of 600 and 550 degreesC afforded composite TiO2/VO2 films. These films exhibited photoinduced hydrophilicity, photocatalysis and a thermochromic switching temperature of 51 degreesC.

Shape Selectivity by Guest‐Driven Restructuring of a Porous Material

A flexible metal-organic framework selectively sorbs para- (pX) over meta-xylene (mX) by synergic restructuring around pX coupled with generation of unused void space upon mX loading. The nature of the structural change suggests more generally that flexible structures which are initially mismatched in terms of fit and capacity to the preferred guest are strong candidates for effective molecular separations.

Thermochromic Coatings for Intelligent Architectural Glazing

Thermochromic glazing is a type of intelligent glazing; one where the properties of the glazing change according to some external stimulus. More particularly a thermochromic window is a device that changes its transmission and reflectance properties at a critical temperature (Tc). Atthis specific temperature the material undergoes a semi-conductor to metal transition. At temperatures lower than Tc the window lets all of the solar energy that hits it through. At emperatures above Tc the window reflects the infra-red portion of solar energy. In such a way thermochromic windows may help reduce air conditioning and heating costs leading to more energy efficient buildings. This review details the nature of the semi-conductor to metal transition and indicates how substitutional doping within a crystal lattice can be used to manipulate and fine tune the critical temperature. Also detailed is the underlying science and methodologies so far employed in the production of thermochromic thin films.

Catalytic Response and Stability of Nickel/Alumina for the Hydrogenation of 5-Hydroxymethylfurfural in Water.

The catalytic response of Ni on Al2O3 obtained from Ni-Al layered double hydroxides was studied for the liquid-phase hydrogenation of hydroxymethyl furfural to tetrahydrofuran-2,5-diyldimethanol (THFDM) in water. The successive calcination and reduction of the precursors caused the removal of interlayer hydroxyl and carbonate groups and the reduction of Ni(2+) to Ni(0). Four reduced mixed oxide catalysts were obtained, consisting of different amount of Ni metal contents (47-68 wt%) on an Al-rich amorphous component. The catalytic activity was linked to Ni content whereas selectivity was mainly affected by reaction temperature. THFDM was formed in a stepwise manner at low temperature (353 K) whereas 3-hydroxymethyl cyclopentanone was generated at higher temperature. Coke formation caused deactivation; however, the catalytic activity can be regenerated using heat treatment. The results establish Ni on Al2O3 as a promising catalyst for the production of THFDM in water.

Interface control by chemical and dimensional matching in an oxide heterostructure

Interfaces between different materials underpin both new scientific phenomena, such as the emergent behaviour at oxide interfaces, and key technologies, such as that of the transistor. Control of the interfaces between materials with the same crystal structures but different chemical compositions is possible in many materials classes, but less progress has been made for oxide materials with different crystal structures. We show that dynamical self-organization during growth can create a coherent interface between the perovskite and fluorite oxide structures, which are based on different structural motifs, if an appropriate choice of cations is made to enable this restructuring. The integration of calculation with experimental observation reveals that the interface differs from both the bulk components and identifies the chemical bonding requirements to connect distinct oxide structures.

Photocatalytic Water Oxidation by a Pyrochlore Oxide upon Irradiation with Visible Light: Rhodium Substitution Into Yttrium Titanate†

A stable visible-light-driven photocatalyst (λ≥450 nm) for water oxidation is reported. Rhodium substitution into the pyrochlore Y2 Ti2 O7 is demonstrated by monitoring Vegards law evolution of the unit-cell parameters with changing rhodium content, to a maximum content of 3 % dopant. Substitution renders the solid solutions visible-light active. The overall rate of oxygen evolution is comparable to WO3 but with superior light-harvesting and surface-area-normalized turnover rates, making Y2 Ti1.94 Rh0.06 O7 an excellent candidate for use in a Z-scheme water-splitting system.