David Gordon Billing

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Verified

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• PhD
• Professor (Full) & Assistant Dean : Operations and Infrastructure at University of the Witwatersrand

This paper investigates the thermal decomposition of bismuth citrate sol–gel precursors using thermogravimetry, derivative thermogravimetry and differential thermal analysis, as well as Fourier transform infrared spectroscopy and powder X-ray diffraction with Rietveld refinement analysis. Citric acid effectively complexes Bi3+ to form bismuth citra...

In this work, Chemical Vapour Deposition (CVD) has been used to synthesize boron nitride (BN) nanostructures, particularly nanotubes, and selectively introduce defects into the lattice of the synthesized BN nanostructures through ion implantation. Scanning electron microscopy (SEM) images show clear evidence of BN nanostructures and BN nanotubes (B...

Extensive investigations have been carried out on spinel mixed transition metal oxide-based materials for high-performance electrochemical energy storage applications. In this study, mesoporous Mn-substituted MnxZn1−xCo2O4 (ZMC) ternary oxide microspheres (x = 0, 0.3, 0.5, 0.7, and 1) were fabricated as electrode materials for supercapacitors throu...

Efforts to lower the operating temperature of solid oxide fuel cells include producing electrolytes that are sufficiently conductive and stable below 600 °C. Doped ceria is one such electrolyte being considered. During this study, codoped ceria powders (Ce0.8Sm0.2-xMxO2-δ, M = Bi3+, Zn2+ and x = 0, 0.05, 0.1, 0.15, 0.2) were prepared via coprecipit...

Spin coaters offer an invaluable method of thin film fabrication. Various implementations, both proprietary and open-source exist, offering vacuum and gravity samples chucks. These implementations vary in their reliability, ease-of-use, cost, and versatility. Here we present a novel easy-to-use open-source gravity-chuck type spin coater with minima...

The in situ δ-phase formation for a series of yttrium-doped Bi2O3 materials was studied by Raman spectroscopy and high resolution X-ray diffraction under variable temperature conditions. Contrary to previous reports, for dopant concentrations less than 25%, the cubic ô-phase was not fully stabilized at room temperature - tetragonal phase content wa...

A hydrothermal method was used to synthesize LiFePO4 to explore the effect of the rate of addition of the Li+ precursor to a mixture of the Fe2+ and PO43- precursors. Both the average and local structures were investigated using powder X-ray diffraction, Mössbauer spectroscopy and X-ray absorption spectroscopy. Slower addition rates led to increase...

A prototype application for machine-readable literature is investigated. The program is called pyDataRecognition and serves as an example of a data-driven literature search, where the literature search query is an experimental data set provided by the user. The user uploads a powder pattern together with the radiation wavelength. The program compar...

We investigate a prototype application for machine-readable literature. The program is called "pyDataRecognition" and serves as an example of a data-driven literature search, where the literature search query is an experimental data-set provided by the user. The user uploads a powder pattern together with the radiation wavelength. The program compa...

A structure made of a very thin Pd metal layer at the surface, followed by a SiC layer of varied thickness were deposited onto a c-Si substrate by e-beam evaporation at room temperature. Solid state dewetting of the top metal layer is achieved at near eutectic temperature of Pd/Si phase at 800 °C and we study its effect on the sandwiched SiC semico...

We report on the elastic and magnetic properties of multiferroic Tb0.3Mn20.9O78.8 thin films. The films were deposited on (0 0 1) Si using radio frequency magnetron (RF) sputtering at 50 W and ambient temperature. The elastic properties have been established by surface Brillouin scattering (SBS) after fitting the discrete phonon dispersion in the k...

Diamond-like carbon (DLC) thin films are deposited by unbalanced RF magnetron sputtering at substrate bias voltages to tune the ratio of the sp³ to sp² bonds and hydrogen composition in optimized Ar: CH4 ambient. The effect of substrate bias voltage on the sp² and sp³ bonding ratios and hydrogen concentration is correlated to the physical and elast...

Fundamentally, organic solar cells (OSCs) with a bulk-heterojunction active layer are made of at least two electronically dissimilar molecules, in which photoabsorption in one (donor) generates Frenkel excitons. The formation of free charge carriers emerge after exciton dissociation at the donor:acceptor interface. In the past decade, most of the p...

This study reports on the elastic properties and the lattice thermal conductivity of amorphous Ge2Sb2Te5 and GeTe thin films using surface Brillouin scattering. It is demonstrated that this method allows for the determination of the isotropic elastic constants from the measured surface acoustic phonon frequencies. We found elastic constants of C 11...

Equilibrium phases of the Bi2O3-WO3 system, synthesized using the citrate-gel method with slow cooling, have been systematically investigated for samples with 22–27 mol% WO3. Annealing temperature and content of WO3 were shown to play a significant role in the phases present. Both powder X-ray diffraction and Raman spectroscopy revealed that the ro...

A major noble way to realizing high-efficiency organic solar cell device is the use of ternary blends with non-fullerene acceptors. Although offset in the band gap (E-gap) of the donor/acceptor material is negligible, it still exhibits ultra-fast and efficient charge separation. Regardless of the progress made, device optimization and fundamental u...

Phase-change materials are chalcogenide alloys used for nonvolatile memory applications due to their rapid and reversible structural transformation. ${{\rm In}_3}{{\rm SbTe}_2}$ is a promising candidate that exhibits transitions dependent on thermal conductivity. The minimum lattice thermal conductivity of amorphous ${{\rm In}_3}{{\rm SbTe}_2}$ is...

Ternary transition metal oxides are promising advanced materials for use as electrode components in electrochemical energy storage systems. However, low electronic/ionic conductivity hinder practical applications. In this study, ternary Mn‐Ni‐Co oxide nanoparticles were encapsulated in carbon nanosheets, to improve the electrical conductivity and s...

Elastic properties of TaN films on (001)Si are investigated by surface Brillouin scattering (SBS). The velocity dispersion is obtained from Brillouin frequency shifts and surface acoustic wave phase velocities derived from measured SBS spectra. The observed Rayleigh surface acoustic and Sezawa waves indicate a soft on hard configuration. The elasti...

Li 4 Ti 5 O 12 (LTO) and its doped analogues Li 4 Ti 4.95 M 0.05 O 12 (M = Al ³⁺ , Co ³⁺ , Ni ²⁺ , and Mg ²⁺ ) were synthesized and characterized using in situ PXRD to monitor the phase transitions during the sol–gel synthesis of the spinel material. These results are complimented by thermogravimetric analysis, which illustrates the decomposition o...

Eu-doped ZnO (ZnO:Eu³⁺) thin films deposited by RF magnetron sputtering have been investigated to establish the effect of annealing on the red photoluminescence. PL spectra analysis reveal a correlation between the characteristics of the red photoluminescence and the annealing temperature, suggesting efficient energy transfer from the ZnO host to t...

This paper highlights materials development strategies of single-, double-, and triple-doped oxides involving bismuth and rare-earth elements. The work presented focused on crystalline phase manipulation and low temperature stabilization of pertinent oxide ion conductive phases. Synthetic routes have utilized mixed metal sol-gel precursors, thermal...

Mixed cation perovskites currently achieve very promising efficiency and operational stability when used as the active semiconductor in thin‐film photovoltaic devices. However, an in‐depth understanding of the structural and photophysical properties that drive this enhanced performance is still lacking. Here the prototypical mixed‐cation mixed‐hali...

We report an investigation on the effect of oxygen flow rate on the structural and optical properties of zinc oxide thin films prepared by RF magnetron sputtering. The structural measurements were carried using grazing incidence X-ray diffraction, atomic force microscopy and Raman spectroscopy. The role of oxygen partial pressure on the crystallini...

The influence of sputtered Pt40Pd57Al3 thin films of varying thickness, in the as-deposited (AD) and annealed (AN) state, was investigated for the electro-oxidation of aqueous SO2. From physical characterisation (scanning electron microscopy (SEM) and grazing incidence X-ray diffraction (GIXRD)), significant differences were found in the morphology...

The synthesis and thermoresponsive behaviour of high purity CuTi2(PO4)3 (CTP) was examined while heating in air and nitrogen at atmospheric pressure. It is known that a spontaneous redox reaction involving the Cu⁺ cations that are contained in the Ti2(PO4)3⁻ crystal structure converts the CTP phase to the related Cu0.5Ti2(PO4)3 (CTP2) phase when he...

The effects of implantation of Samarium ions (Sm⁺), a rare earth ion (RE) on the properties of ZnO films grown on Si (001) substrate by RF sputtering system are presented. The structural properties of the virgin and Sm–implanted ZnO thin films were investigated by Atomic force microscopy, Rutherford backscattering spectroscopy and Raman spectroscop...

Mn substituted MnxZn1−xCo2O4 (x = 0, 0.3, 0.5, 0.7, 1) oxides were synthesized by a facile co-precipitation method followed by calcination at 600 °C. The presence of manganese ions causes appreciable changes in the structural and magnetic properties of the Mn-substituted ZnCo2O4. The morphologies, structures, and electronic properties of Mn-Zn-Co o...

Down conversion has been applied to minimize thermalization losses in photovoltaic devices. In this study, terbium-doped ZnO (ZnO:Tb³⁺) thin films were deposited on ITO-coated glass, quartz and silicon substrates using the RF magnetron sputtering technique fitted with a high-purity (99.99%) Tb³⁺-doped ZnO target (97% ZnO, 3% Tb) for use in organic...

Mixed ternary spinel-type oxides Mn x Ni 1-x Co 2 O 4 (x = 0, 0.5, 1) were synthesized using a citrate sol-gel route. The morphologies and structures of the mixed oxide nanoparticles were characterized using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier-Transform Infrared Spectroscop...

A series of spinel-type MnxNi1-xCo2O4 (x = 0, 0.3, 0.5, 0.7, 1) oxides were synthesized by using a citrate sol-gel technique. The structural, magnetic and electronic properties of the oxides with different Mn content were investigated using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), vibrating sample magnetometer (VSM)...

This work investigates the viability and outlines the current challenges in electrochemical quartz crystal nanobalance (EQCN) experiments on supported Pt catalysts. EQCN experiments involving Pt supported on 2-D “surface-treated graphite sputtered onto quartz crystal” (Pt/MFG-H) catalysts were compared to standard polycrystalline Pt (Ptpoly), which...

One of the pathways responsible for the deactivation of Fischer-Tropsch catalysts is the loss of active metal surface area due to nanoparticle agglomeration. To combat this effect efforts have been made to increase the interaction between the metal nanoparticles and the support using materials like silica. In this study, the supported metal particl...

It is well known that catalysts in fuel cells undergo degradation, which limits the lifetime of the cell [1]. Many degradation mechanisms have been shown to take place, of which the two biggest contributors are Ostwald ripening and carbon oxidation [2]. In order to explain these degradation mechanisms, the anchoring of Pt with its carbon support ne...

Aluminium doped zinc oxide thin films are prepared by Radio Frequency magnetron sputtering in pure argon atmosphere at 100 W. The structural results reveal good film adhesion on a silicon substrate (001). The thin films were then subjected to heat treatment in a furnace under ambient air. The structural, morphological, and optical properties of the...

Pyrochlore and defect fluorite structured materials with A2³⁺B2⁴⁺O7 stoichiometry have a wide variety of potential commercial applications, from solid oxide fuel cell electrolytes to thermal barriers and radioactive nuclei immobilisation matrixes. Previous reported synthetic methodologies for the preparation of these materials that are based on Pb(...

Mesoporous hollow carbon spheres (MHCS) were synthesized (d= 290 nm; carbon shell 20-35 nm) and their hollow morphology was exploited to study the influence of Ru nanoparticles location relative to Co3O4 nanoparticles on the reduction behavior and activity of Co Fischer-Tropsch catalysts. Ru nanoparticles were loaded both inside and outside the MHC...

Three spinel materials were prepared and characterized by in situ powder X-ray diffraction (PXRD) techniques to track their phase changes that occurred in the typical batch synthesis process from a sol–gel mixture to the final crystalline spinel oxide. The materials were also characterized by thermal gravimetric analysis, whereby the materials deco...

We evaluated the chemical sequestration of carbon dioxide into the phosphogypsum from the Lowveld region of South Africa. The phosphogypsum was converted to saleable ammonium sulphate and precipitated calcium carbonate in a modified Merseburg process. The heat from the ammonium carbonate formation exothermicity increased the temperature in the gyps...

The thermal production of 4PbO·PbSO4 was comprehensively studied and characterized for two syntheses routes, i.e. either heating 3PbO·PbSO4·H2O, or a mixture of 4PbO:PbSO4, in air to about 700 °C. In the 3PbO·PbSO4·H2O approach, the formation of an intermediate amorphous phase occurred at around 210 °C with the loss of H2O from the hydrated structu...

When Au is subdivided to the nanoscale its reactivity changes from an inert nature to one of incredible reactivity which is not replicated by other catalysts. When dispersed onto metal oxides such as TiO2, nano-Au has shown high reactivities for a multitude of reduction and oxidation reactions of industrial importance with potential and current use...

The presence of natural organic matter such as humic acid (HA) can influence the behavior of graphene oxide (GO) in the aquatic environment. In this study, zebrafish embryos were analyzed after 5 and 7 days of exposure to GO (100 mg L⁻¹) and HA (20 mg L⁻¹) alone or together. The results indicated that, regardless of the presence of HA, larvae expos...

We evaluated the suitability of phosphogypsum from the Lowveld region of South Africa (LSA), for the manufacturing of building materials, with reference to (1) the National Nuclear Regulator Act 47 of 1999 and (2) the radioactivity associated risks as quantified in terms of the external and internal hazard indices, the activity concentration index...

Carbon spheres (CSs) synthesised by the hydrothermal approach were explored as a model support material for a bimetallic Fe–Co Fischer–Tropsch (FT) catalyst. The CSs were characterised by N2 adsorption–desorption, thermogravimetric analysis, FTIR spectroscopy and powder XRD. If annealed at 900 °C for 4 h, the CSs exhibited an improved surface area,...

Platinum-based alloys are being developed with microstructures similar to nickel-based superalloys for potential high-temperature applications in aggressive environments. Since the chemistries of nickel and platinum are similar, Pt-based alloys can be made with gamma prime ∼Pt3Al precipitates in a gamma (Pt) matrix. Currently, the Pt-Al-Cr-Ru syste...

In this work we present the synthesis and structure-property investigation of anhydrous low porosity borophsophates [1] BPO4 and porous (NH4)0.5M1.25(H2O)2)(BP2O8)(H2O)0.5 M = Co (II), Mn (II) and NH4Fe[BP2O8(OH)] phases. Cristobalite-type BPO4 crystallizes in the tetragonal lattice, space group I-4 (No. 82) [2]. Variable-Temperature Powder X-ray d...

During the last two to three decades the author has been aware of a number of initiatives aimed at stimulating and/or assisting the development of crystallography in various parts of Africa. This includes the CCDC initiatives of the 90's that let to them making the database available to African researchers. As well as a number of attempts to get ba...

During the course of the last couple of years, my collaborators and I have studied a number of catalytic systems using a lab based PXRD facility at our disposal. Of particular interest to us has been the supported catalysts used in Fischer Tropsch catalysis as well as those used in the synthesis of multiwalled carbon nano tubes. These studies have...

The phase behaviour of Fe and Co particles, supported on CaCO3 was studied using mainly in situ PXRD and Mossbauer spectroscopy. This is of interest as these systems can be used as catalysts to produce multi-walled carbon nanotubes (MWCNTs) following appropriate heat treatment and reduction. The Fe-Co/CaCO3 samples were prepared by deposition of th...

The molecular structure of carbonylchlorobis(tri(3-pyridyl)phosphine)rhodium, 1, has been deter-mined by X-ray diffraction methods. The N-protonated trifluoromethanesulfonate (triflate) complex 3 was synthesised as a model compound for the extraction of a rhodium complex bearing amphiphilic ligands which can allow catalyst recycling in the hydrofor...

This study focuses on the use of in situ powder X-ray diffraction (PXRD) and quantitative phase analysis using the Rietveld method to monitor the structural properties of a titania-supported iron (10% Fe/TiO2) pre-catalyst during calcination (oxidation) and activation (reduction) in the temperature range 25–900°C. The TiO2 oxidation study revealed...

Non-ambient conditions are used with increasing regularity in structural studies of crystals and functional materials – this editorial summarizes very briefly the history of environment devices and describes selected recent achievements in this field.

In this paper we report the synthesis and the crystal structure of eight inorganic-organic hybrids containing various lead halides as the inorganic motif and a chiral, primary ammonium cation as the organic constituent. The organic cation investigated is6H11C*H(CH3)NH3)+ and both the) and) as well as the racemicS) forms were used.Within the structu...

The structural and magnetic properties of Ho substituted BiFeO3 (BHFO) have been investigated using 57Fe Mössbauer spectroscopy and X-Ray diffraction (XRD) as a function of temperature. The Mössbauer spectrum obtained at room temperature for the as-synthesized BHFO sample exhibits broadened features due to the hyperfine field distributions related...

High pressure–temperature (P–T) phases of the ZrxHf1−xO2 (x=0.5) solid-solution have been stabilised in a CO2 laser heated diamond anvil cell. At room-temperature the monoclinic to orthorhombic-I structural transformation is initiated at 5–8GPa. The X-ray diffraction (XRD) studies show these two phases coexist to above ∼15GPa. A progressive increas...

Diammonium cations of general formula (H3N–R–NH3) have been used as templating moieties on lead(II) halide motifs, forming a variety of inorganic–organic nanocomposites. The R group can have simple, straight alkyl chains, which if even-membered and greater than ethane, form 2-D layers based on the RbAlF4 structure type, as found in [(H3N(CH2)4NH3)P...

Four inorganic-organic hybrid materials that consist of 2-D layers of corner-sharing lead(II) iodide octahedra separated by alkylammonium chains have been crystallized and characterized via single-crystal XRD (SCXRD). The four hybrids, represented by the general formula [(C(n)H(2n+1)NH(3))(2)PbI(4)] and abbreviated C(n)PbI, exhibit multiple reversi...

The novel crystal structures of seven compounds which combine 2-phenylethylammonium cations and perhalometallate anions, all with the general formula (C8H9NH3+)2 MX42−, were determined to establish the effect of metal atom and halogen ligand substitution on the structures and hydrogen bonding interactions. Five of the structures, bis(2-phenylethyla...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The title compound, {(C(8)H(20)N(2))[PbBr(4)]}(n), crystallizes as an inorganic-organic hybrid with alternating layers of diammonium cations and two-dimensional corner-sharing PbBr(6) octahedra extending parallel to the bc plane, which are eclipsed relative to one another. Both PbBr(6) octahedra and the organic cation exhibit 1 symmetry. The cation...

The title compound, {(C8H20N2)[PbCl4]}n, crystallizes as an layered inorganic–organic hybrid perovskite-type structure. Corner-sharing PbCl6 octahedra extend parallel to the ac plane. Adjacent layers are staggered relative to one another, with diammonium cations separating these layers. The cations exhibit overline{1} symmetry and interact with the...

The title compound, {(C8H20N2)[PbI4]}n, is an inorganic–organic hybrid. The structure is composed of alternate layers of two-dimensional corner-sharing PbI6 octahedra (overline{1} symmetry) and 1,4-bis(ammoniomethyl)cyclohexane cations (overline{1} symmetry) extending parallel to the bc plane. The cations interact with the inorganic layer via N—H.....

The title compound, {(C8H20N2)[PbBr4]}n, crystallizes as an inorganic–organic hybrid with alternating layers of diammonium cations and two-dimensional corner-sharing PbBr6 octa­hedra extending parallel to the bc plane, which are eclipsed relative to one another. Both PbBr6 octa­hedra and the organic cation exhibit symmetry. The cations inter­act vi...

The title compound, {(C8H20N2)[PbCl4]}n, crystallizes as an layered inorganic–organic hybrid perovskite-type structure. Corner-sharing PbCl6 octa­hedra extend parallel to the ac plane. Adjacent layers are staggered relative to one another, with diammonium cations separating these layers. The cations exhibit symmetry and inter­act with the inorganic...

The title compound, {(C8H20N2)[PbI4]}n, is an inorganic–organic hybrid. The structure is composed of alternate layers of two-dimensional corner-sharing PbI6 octa­hedra ( symmetry) and 1,4-bis­(ammonio­meth­yl)cyclo­hexane cations ( symmetry) extending parallel to the bc plane. The cations inter­act with the inorganic layer via N—H⋯I hydrogen bondin...

In the the title compound, C29H26N2O2, two strong intra­molecular O—H⋯N hydrogen bonds involving the hydr­oxy and imine groups generate S(6) ring motifs. The dihedral angles between the pairs of terminal benzene rings are 89.8 (2) and 87.8 (2)°.