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41.
The vortex dynamics at microwave frequencies in YBa2Cu3O7-δ (YBCO) films have been studied. We observe a peak in the microwave (4.88 and 9.55 GHz) surface resistance in some films in
magnetic fields up to 0.8 T. This is associated with the ‘peak-effect’ phenomenon and reflects the order-disorder transformation
of the flux line lattice near the transition temperature. Introduction of artificial pinning centers like columnar defects
created as a result of irradiation with 200 MeV Ag ion (at a fluence of 4×1010 ions/cm2) leads to the suppression of the peak in films previously exhibiting ‘peak effect’. 相似文献
42.
M.R. Pai 《Journal of Physics and Chemistry of Solids》2006,67(7):1502-1509
The catalytic properties and reduction behavior of mixed metal oxides with nominal compositions of LaxTh1−x(VO3−δ)4, where 0.0 ≤ x ≤ 1.0, have been investigated as a function of the value of x. These compositions were synthesized by ceramic route and characterized using powder X-ray diffraction, differential thermal analysis, and temperature-programmed reduction/oxidation/desorption techniques. The substituted samples were comprised of two distinct phases, one corresponding to tetragonal thorium metavanadate with partial substitution at A-sites, i.e. LaxTh1−x(VO3−δ)4, and the other a new phase identified as LaV4O11+δ. Both these phases exhibited considerable oxygen non-stoichiometry, depending upon the extent of substitution. Nevertheless, no significant change was observed in their respective crystal symmetry. Further, the substituted samples showed more reproducible redox behavior and also an improved catalytic activity for CO oxidation reaction. A definite correlation is found to exist between the micro-structural defects generated in the above-mentioned two phases because of the oxygen ion vacancies, resultant enhancement in thermal diffusitivity of lattice oxygen, and finally the catalytic activity of the substituted mixed oxides. It is envisaged that a kind of synergism between the micro-structural defects existing in the two inter-grown phases generated simultaneously during the synthesis may control the catalytic properties of composite metal oxide systems. 相似文献
43.
K. I. Gnanasekar M. Sharon R. Pinto A. S. Tamhane S. C. Purandare S. P. Pai L. C. Gupta R. Vijayaraghavan 《Zeitschrift für Physik B Condensed Matter》1995,99(2):173-177
Structural and superconducting properties of the system Lu1?x Ca x Ba2 Cu3O7?δ, both in bulk as well as thin film form, have been investigated. Presence of large Ca-ions at the Lu-sites is responsible for phase stability (in 1–2–3 phase) in bulk. In argon annealed tetragonal samples (δ:1) superconductivity is reinstated as in these samples, presence of Ca-ions lead to the generation of holes in the Cu?O planes. In oxygen annealed bulk samples and thin films, there is a large depression ofT c due to divalent Ca-ions present in concentrationx<0.2. Our data indicate that this depression ofT c is likely due to overdoping effect. 相似文献
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The electrical resistivity and Seebeck coefficients of pure MnO single crystals have been measured above the Néel temperature. The material is p type in this temperature range. The results are interpreted on the basis of small-polaron hopping involving charge carriers in one or more sets of transport levels. 相似文献
48.
The online version of the original article can be found at 相似文献
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50.
R.N. Nottenburg K. Rajeshwar J. DuBow V.R. Pai Verneker 《Solid State Communications》1979,31(11):777-780
A.C. electrical conductivity of potassium perchlorate (KP) has been measured in the temperature range 25–325°C at frequencies ranging from 50–500 Hz using an automated technique. The results are interpreted in terms of a novel mechanism involving Schottky defects in the anion sublattice and Frenkel defects in the cation sublattice. The conductivity behavior of KP is compared with literature data on similar low-symmetry systems containing polyatomic ions. 相似文献