Browsing by Author "Du Plessis, J"

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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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    Fabrication, structural characterization and testing of a nanostructured tin oxide gas sensor
    (Institute of Electrical and Electronics Engineers (IEEE), 2009-04-07) Partridge, JG; Field, MR; Sadek, AZ; Kalantar-Zadeh, K; Du Plessis, J; Taylor, MB; Atanacio, AJ; Prince, KE; McCulloch, DG
    A nanostructured SnO 2 conductometric gas sensor was produced from thermally evaporated Sn clusters using a thermal oxidation process. SnO 2 clusters were simultaneously formed in an identical process on a Si 3 N 4 membrane featuring an aperture created by a focused ion beam (FIB). Clusters attached to the vertical edges of the aperture were imaged using a transmission electron microscope. The original morphology of the Sn cluster film was largely preserved after the thermal oxidation process and the thermally oxidized clusters were found to be polycrystalline and rutile in structure. NO 2 gas sensing measurements were performed with the sensor operating at various temperatures between 25degC and 290degC. At an operating temperature of 210degC, the sensor demonstrated a normalized change in resistance of 3.1 upon exposure to 510 ppb of NO 2 gas. The minimum response and recovery times for this exposure were 45 s and 30 s at an operating temperature of 265degC. The performance of the SnO 2 sensor compared favorably with previously published results. Finally, secondary ion mass spectrometry and X-ray photoelectron spectroscopy were used to establish the levels of nitrogen present in the films following exposure to NO 2 gas. © Copyright 2009 IEEE
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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.