Data on the 205 T1 NMR frequency shift and linewidth due to the magnetic field variation in the mixed state of Tl2Ba2Ca2Cu30io are presented. These data, which are commonly used to extract the London penetration depth, show a near linear temperature dependence at T < T c . We offer an explanation of this effect as being caused by thermal fluctuations of vortices in weakly coupled layered systems. We argue that the fluctuations cannot be ignored in interpretation of NMR and muon-spin-resonance data for materials with large penetration depths even at low T. PACS numbers: 74.25.Nf, 74.40.+k In weakly coupled layered superconductors, thermal fluctuations of vortices strongly influence the thermodynamics of the system in a magnetic field. This has been observed in "non-mean-field" dependence of the magnetization M on temperature T and magnetic field H in Bi 2 Sr 2 CaCu 2 0 8 (Bi-2212) and Bi 2 Sr2Ca 2 Cu30io (Bi-2223) well under the mean-field transition temperature T C Q. At a temperature T*, a few kelvins below T c o, M is field independent [1-3], The effect has been explained quantitatively by the contribution of fluctuating vortices to the system entropy [4].For high anisotropies and H
Uniform films of the high Tc superconductor YBa2Cu3O7−δ have been prepared by organometallic chemical vapor deposition using the volatile metalorganic precursors Cu(acetylacetonate)2, Y(dipivaloylmethanate)3, and Ba(heptafluorodimethyloctanedionate)2. With argon as a carrier gas and water vapor as a reactant, film growth rates of 10–30 nm/min are achieved. After annealing under oxygen, energy dispersive x-ray analysis, profilometry, and x-ray diffraction data reveal that such YBa2Cu3O7−δ films on [100] single-crystal MgO have good compositional and dimensional uniformity as well as preferential orientation of crystallite c axes perpendicular to the substrate surface. Four-probe resistivity measurements reveal the onset of superconductivity at ∼90 K and zero resistance by 66.2 K.
SrTiO3 thin films were deposited by low-pressure organometallic chemical vapor deposition. Titanium isopropoxide, Sr(dipivaloylmethanate)2, oxygen, and water vapor were used as reactants, and argon was used as a carrier gas. Growth rates ranging from 0.3 to 4.5 μm/h were obtained on (0001) sapphire substrates at 600–850 °C. Highly textured SrTiO3 films with a [111] orientation were obtained at a growth temperature of 800 °C. The growth parameters which influenced the composition, phase stability, morphology, and texture of the thin films were examined.
Films of the Tl-Ba-Ca-Cu-O high Tc superconductor can be prepared by either of two organometallic chemical vapor deposition routes. Ba-Ca-Cu-O films are first prepared on yttria-stabilized zirconia using the volatile precursors Ba(heptafluorodimethyloctanedionate)2, Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2. Deposition is carried out at 5 Torr pressure with argon as the carrier gas and water vapor as the reactant gas. Thallium is next incorporated in these films either by vapor diffusion using bulk Tl-Ba-Ca-Cu-O as the source, or by organometallic chemical vapor deposition using Tl(cyclopentadienide) as the source. The latter deposition is carried out at atmospheric pressure with an argon carrier and water-saturated oxygen reactant, followed by rapid thermal annealing. Both types of films consist primarily of the TlBa2Ca2Cu3Ox phase, have preferential orientation of the CuO planes parallel to the substrate surface, and exhibit onset of superconductivity at ∼120 K with zero resistance by 100 K.
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