62 research outputs found
Cation Valences and Multiferroic Properties of EuTiO3 Co-Doped with Ba and Transition Metals of Co/Ni
No full textEu1−xBaxTi1−yMyO3 (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray photoelectron spectroscopy revealed the mixed valences of Eu2+/Eu3+ and Ti4+/Ti3+ in EuTiO3 and Eu0.7Ba0.3TiO3, as well as some oxygen vacancies required to keep the charge neutrality. The co-doping of Co2+/Ni2+ in Eu0.7Ba0.3TiO3 resulted in the disappearance of oxygen vacancies, as a result of a reduction in Ti3+ numbers and an increase in Eu3+ numbers. On the other hand, Ba2+ doping led to an increased lattice parameter due to its larger ionic size than Eu2+, whereas the Co2+/Ni2+ co-doping resulted in smaller lattice parameters because of the combined effects of ionic size and variation in the oxygen-vacancy numbers. Eu0.7Ba0.3TiO3 exhibited a clear ferroelectricity, which persisted in the Co2+/Ni2+ co-doped samples until the doping levels of y = 0.05 and 0.10, respectively. Eu0.7Ba0.3TiO3 remained to be antiferromagnetic with a reduced transition temperature of 3.1 K, but co-doping of Co2+/Ni2+ turned the samples from antiferromagnetic to ferromagnetic with transition temperatures of 2.98 K and 2.72 K, respectively. The cause for such a transition could not be explained by the larger lattice volume, oxygen vacancies and mixed valences of Eu2+/Eu3+, which were proposed in previous works. Instead, it was more likely to arise from a large asymmetric distortion of the Eu–O polyhedron introduced by the aliovalent doping, which promotes the admixture of Eu 5d and 4f states
The Effects of Nickel Substitution on Bismuth Ferrite
No full textAbstractIn this paper, we studied the electrical conduction and spectroscopic properties of the Ni-doped BiFeO3 (BFO), which were prepared by the sol–gel method and sintered into powders or compact pellets. The changes of sintering conditions due to the addition of Ni were studied and the solubility of Ni in BFO was estimated. Photoluminescence measurements were carried out for the Ni-doped BFO samples and observed four emissions at about 451, 468, 513, and 689nm, respectively. The resistivity of the Ni doped BFO was reduced by more than three orders of magnitude than the un-doped BFO. The conductivity vs. temperature measurements revealed three activation energies, whose levels in the band gap matched well with the observed PL emission wavelengths
Interfacial diffusion and exchange bias in the oxide multilayer Zn<sub>0.7</sub> Ni<sub>0.3</sub> Fe<sub>2</sub> O<sub>4</sub> /BiFeO<sub>3</sub> /SrTiO<sub>3</sub>
No full textSingle Crystal Growth and Characterisations of Transition Metal Ion Doped TTB Ferroelectrics
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The Economic Consequences of IPO Spinning
No full textUsing a sample of fifty-six companies going public in 1996--2000 in which top executives received allocations of other hot initial public offerings (IPOs) from the bookrunner, a practice known as spinning, we examine the consequences of spinning. The fifty-six IPOs had first-day returns that were, on average, 23% higher than similar IPOs. The profits collected by these executives were only a small fraction of the incremental amount of money left on the table by their companies when they went public. These companies were dramatically less likely to switch investment bankers in a follow-on offer: only 6% of issuers whose executives were spun switched underwriters, whereas 31% of other issuers switched. These findings suggest that the spinning of executives accomplished its goal of affecting corporate decisions. The Author 2010. Published by Oxford University Press on behalf of The Society for Financial Studies. All rights reserved. For Permissions, please e-mail: [email protected]., Oxford University Press.
Growth and Characterization of Pure and Doped SnO2 Films for H2 Gas Detection
No full textAbstractPure and the transition metal (TM) doped SnO2 films were prepared by the sol-gel method. The surface morphology and microstructure of the grown films were characterized by a wide range of techniques. Generally, various TM doping resulted in a reduction of the particle size, as well as a smaller size of various surface features. The films were tested for the gas sensing applications. In the air containing 500ppm H2, the optimum operating temperature for the pure SnO2 films was 250 oC, which showed a sensitivity of S=3.9 and a recovery time of 84s. Doping of 5 at% W increased the sensitivity significantly (S=25.8) at the same operating temperature, while the recovery time was reduced to 72s. For the 5at% Pd doped SnO2 films, the sensitivity was only slightly improved (S=4.4), however they showed the quickest recovery time of 60s. Doping of Mn did not improve the H2 sensing sensitivity and the doped films showed a poor thermal stability at the elevated temperatures
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