G.C. Georgiadis

Bio: G.C. Georgiadis is an academic researcher from Imperial College London. The author has contributed to research in topics: X-ray photoelectron spectroscopy & Geology. The author has an hindex of 2, co-authored 4 publications receiving 47 citations.

Spectroscopic studies of atmospheric degradation of Y-Ba-Cu-O superconducting materials

Abstract: Atmospheric degradation reactions of the ceramic superconducting oxides YBa2Cu3O7 and YBa2Cu4O8 and of (YBa2Cu3O7)1−xAgx (0 < x < 0.5) composites have been studied by infrared reflectance spectroscopy. Buildup of BaCO3 on the sample surfaces is accompanied by development of Reststrahlen features associated with internal modes of the carbonate ion. The rate of degradation of the YBa2Cu4O8 and the silver composites (YBa2Cu3O7)1−xAgx under exposure to water vapour saturated air is much lower than for YBa2Cu3O7 itself.

Diatomaceous Silica in Environmental Applications: A Case Study from the Lacustrine Deposit of Limnos Island, Aegean Sea, Greece

Abstract: Diatomitic and clastic-volcanoclastic marly samples from the Paranisia area of Limnos Island, were studied mineralogically by X-ray diffraction (XRD), chemically by X-ray fluorescence spectroscopy (XRF) and morphologically by scanning electron microscopy (SEM-EDS), together with some physical properties such as the insulation block density, specific surface area and porosity. The diatomaceous samples were classified as porcelaneous or clayey (moler type) diatomite. Opal-CT forms microplates disseminated in the groundmass and are diagenetically formed in expense of opal-A dissolution. The purest diatomaceous beds have been transformed into opaline beds (opal-CT-rich rocks), whereas the clayey beds were not influenced by diagenetic transformations. The studied diatomites from Limnos Island are suitable materials for environmental uses, as an absorbent, for the production of insulation bricks or as lightweight aggregates.

A photoemission study of Bi3.6Pb0.4Sr3Ca2.4Er0.7Cu4O16 in normal and superconducting states

Abstract: Photoemission spectra of single crystalline Bi 3.6 Pb 0.4 Sr 3 Ca 2.4 Er 0.7 Cu 4 O 16 have been measured in the photon energy range 20 eV hv T c . The symmetry of the states is investigated by varying the polarisation of the incident radiation relative to the sample surface. Again there are no indications of changes at T c .

Core and valence level photoemission studies of oxygen annealed Y2Ba4Cu6+NO14+N (N=0, 1, 2) surfaces

Abstract: Atomically clean surfaces of the 123, 247 and 124 YBaCu oxide superconductors have been prepared for photemission studies by in situ oxygen annealing. They are characterised by simple lineshapes for the 01s core level in XPS and the absence of satellite structure at 9.5eV in valence level UPS. Atomic ratios inferred from the intensities of XPS core lines demonstrate barium segregation at the surfaces of all three materials.

Metal oxide composites in conductometric gas sensors: Achievements and challenges

Abstract: The features of conductometric gas sensors based on metal oxide composites are considered. The methods of the composites forming and the advantages of their using in the development of gas sensors are discussed. It is given the analysis of the factors that reduce the effectiveness of the composite using in conductometric gas sensors and can restrict application of nanocomposites in these devices. Technology features of composite synthesis and device fabrication, which should be taken into account while designing and fabricating sensors based on metal oxide composites, are considered. The mechanisms explaining the operation of conductometric gas sensors based on metal oxide composites are also discussed.

Semiconducting transition metal oxides

Abstract: Open shell transition metal oxides are usually described as Mott or charge transfer insulators, which are often viewed as being disparate from semiconductors. Based on the premise that the presence of a correlated gap and semiconductivity are not mutually exclusive, this work reviews electronic structure calculations on the binary 3d oxides, so to distill trends and design principles for semiconducting transition metal oxides. This class of materials possesses the potential for discovery, design, and development of novel functional semiconducting compounds, e.g. for energy applications. In order to place the 3d orbitals and the sp bands into an integrated picture, band structure calculations should treat both contributions on the same footing and, at the same time, account fully for electron correlation in the 3d shell. Fundamentally, this is a rather daunting task for electronic structure calculations, but quasi-particle energy calculations in GW approximation offer a viable approach for band structure predictions in these materials. Compared to conventional semiconductors, the inherent multivalent nature of transition metal cations is more likely to cause undesirable localization of electron or hole carriers. Therefore, a quantitative prediction of the carrier self-trapping energy is essential for the assessing the semiconducting properties and to determine whether the transport mechanism is a band-like large-polaron conduction or a small-polaron hopping conduction. An overview is given for the binary 3d oxides on how the hybridization between the 3d crystal field symmetries with the O-p orbitals of the ligands affects the effective masses and the likelihood of electron and hole self-trapping, identifying those situations where small masses and band-like conduction are more likely to be expected. The review concludes with an illustration of the implications of the increased electronic complexity of transition metal cations on the defect physics and doping, using as an example the diversity of possible atomic and magnetic configurations of the O vacancy in TiO(2), and the high levels of hole doping in Co(2)ZnO(4) due to a self-doping mechanism that originates from the multivalence of Co.

Preparation, characterisation and applications of thin films for gas sensors prepared by cheap chemical method

Abstract: The physical properties of pure and doped (Ni, Os, Pd and Pt) SnO 2 thin films, prepared by using a chloride-based inorganic sol–gel route, have been reported. These properties were investigated by using differential scanning calorimetry and thermogravimetric (DSC/TG), FTIR, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. Microsensors for gas detection were also fabricated and tested in various atmospheres (nitrogen oxide, carbon monoxide, ethanol, methanol and methane). The dopants affected the coating properties depending on the formation of nanoparticles. Furthermore the gas-sensing properties towards reducing and oxidising gases were found to be dependent on the nature of doping element. An array consisting of the manufactured sensors has been arranged and examples of applications for “electronic nose” are given.