Browsing by Author "Alim, MA"

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    Electrical conductivity and defect disorder of tantalum‐doped TiO2
    (John Wiley & Sons, 2017-05-02) Alim, MA; Bak, T; Atanacio, AJ; Du Plessis, J; Zhou, MF; Davis, J; Nowotny, J
    The present work reports the electrical properties of polycrystalline Ta‐doped TiO2 (0.39 at.% Ta) determined in situ at elevated temperatures (1173‐1323 K) in the gas phase of controlled oxygen activity (10−12 Pa to 105 Pa). The effect of oxygen activity on the electrical conductivity and thermoelectric power of TiO2 is discussed in terms of defect disorder, including (1) the intrinsic electronic disorder that is governed by electronic compensation in the strongly reducing regime, (2) the extrinsic electronic disorder that is governed by electronic charge compensation in the reducing regime, and (3) the extrinsic ionic disorder that is governed by ionic compensation in the oxidizing regime. It is shown that tantalum ions are incorporated into the titanium sublattice of TiO2 leading to the formation of donor‐type energy levels. The Arrhenius‐type plot of the electrical conductivity data leads to the determination of the formation enthalpy terms. The obtained results are considered in terms of the effect of tantalum and oxygen activity on the defect disorder and the associated key performance‐related properties in the light‐induced partial water oxidation. © 2017 The American Ceramic Society
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    Electrical properties and defect chemistry of indium-doped TiO2, thermoelectric power
    (Springer Nature Switzerland AG, 2014-12-30) Nowotny, J; Alim, MA; Bak, T; Atanacio, AJ; Malik, A
    This work studied the effect of indium on the semiconducting properties of TiO2 (rutile) at elevated temperatures (1023-1273 K) in the gas phase of controlled oxygen activity in the range of 10(-16) Pa< p(O-2)< 10(5) Pa. The studies were performed using the measurements of thermoelectric power of In-doped TiO2 (0.4 at.% In) as a function of oxygen activity and temperature. The obtained data indicates that indium is incorporated into the TiO2 lattice according to the dual mechanism leading to the formation of donors and acceptors in the interface (surface and grain boundary) layer and the bulk phase, respectively. This effect is considered in terms of a quasi-isolated surface layer that differs from the bulk phase in terms of semiconducting properties and the related defect disorder. © 2014 Springer Nature Switzerland AG.
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    Electrical properties and defect chemistry of indium-doped TiO2: electrical conductivity
    (The Electochemical Society, 2014-08-13) Nowotny, J; Malik, A; Alim, MA; Bak, T; Atanacio, AJ
    This work reports the electrical conductivity of indium-doped TiO2 at elevated temperatures (1023 K - 1273 K) and in the gas phase of controlled oxygen activity in the range 10(-16) Pa
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    Photocatalytic properties of Ta-doped TiO2
    (Springer Nature, 2017-06-10) Alim, MA; Bak, T; Atanacio, AJ; Ionescu, M; Kennedy, BJ; Price, WS; Du Plessis, J; Pourmahdavi, M; Zhou, MF; Torres, AM; Nowotny, J
    This work reports the effect of tantalum (0.1–1 at.% Ta) on the photocatalytic performance of TiO2 annealed at 1373 and 1673 K in air. It was shown that addition of tantalum resulted in an increase of photocatalytic activity of TiO2 for the specimens annealed at 1373 K. However, the activity of the Ta-doped TiO2 specimens annealed at 1673 K was reduced. The effect of tantalum on the photocatalytic performance at 1373 K was rationalised in terms of an increased concentration of titanium vacancies acting as the active surface sites, and increased charge transport. In this work, it was also shown that the band gap reduction due to tantalum incorporation had little effect on photocatalytic performance. The effect of annealing at 1673 K on photocatalytic activity was explained in terms of reduced surface segregation of tantalum. © 2017 Springer Nature Switzerland AG.
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    Segregation in titanium dioxide co-doped with indium and niobium
    (American Ceramic Society, 2016-10-06) Atanacio, AJ; Alim, MA; Ionescu, M; Nowotny, J
    This work reports the effect of oxygen activity on surface segregation for TiO2 co-doped with two cations, indium and niobium (0.076 at.% In + 0.103 at.% Nb). In this work, we studied the effect of annealing at 1273 K in the gas phase of controlled oxygen activity on surface segregation of both ions. The applied oxygen activity included pure oxygen, p(O2) = 100 kPa, and argon, p(O2) = 10 Pa. The segregation-induced concentration gradients were determined using both secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The obtained results indicate that annealing of the studied TiO2 specimens in argon results in cooperative segregation of both ions leading to the formation of a surface structure involving comparative concentrations of both cations. However, annealing in oxygen results in preferential segregation of indium leading to the formation of a In2TiO5-type surface structure. The obtained results are considered in terms of the effect of multicomponent segregation on processing of the surface layer with controlled properties that are desired for specific applications. The present work indicates that oxygen activity may be used as the parameter in surface engineering of the solid solution. © 2016 The American Ceramic Society
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    Towards sustainable energy. Generation of hydrogen fuel using nuclear energy
    (Elsevier Ltd., 2016-06-03) Nowotny, J; Hoshino, T; Dodson, JR; Atanacio, AJ; Ionescu, M; Peterson, VK; Prince, KE; Yamawaki, M; Bak, T; Sigmund, W; Veziroglu, TN; Alim, MA
    The increasing demand for sustainable energy results in the development of new technologies of energy generation. The key objective of hydrogen economy is the introduction of hydrogen as main energy carrier, along with electricity, on a global scale. The key goal is the development of hydrogen-related technologies needed for hydrogen generation, hydrogen storage, hydrogen transportation and hydrogen distribution as well as hydrogen safety systems. It is commonly believed that hydrogen is environmentally clean since its combustion results in the formation of water. However, the technology currently employed for the generation of hydrogen from natural gas, does in fact lead to the emission of greenhouse gases and climate change. Therefore, the key issues in the introduction of hydrogen economy involve the development of environmentally clean hydrogen production technology as well as storage and transport. The clean options available for hydrogen generation using nuclear energy; such as advanced nuclear fission and, ultimately, nuclear fusion, are discussed. The latter, which is environmentally clean, is expected to be the primary approach in the production of hydrogen fuel at the global scale. The present work considers the effect of hydrogen on properties of TiO2 and its solid solutions in the contexts of photocatalytic energy conversion and the effect of tritium on advanced tritium breeders. © 2016 Hydrogen Energy Publications LLC.