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Register a new userStructure and physical properties of superconducting compounds Y(La)-Ba(Sr)-Cu-O
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The structure and physical properties of superconducting compounds Y(La)-Ba(Sr)-Cu-O are studied, the compounds being prepared by the method of cryogenic dispersion of a charge consisting of premix oxides and carbonates. Electrical conductivity and critical current density of the superconductors are measured over a wide temperature range of 10~$mK$ to 300~$K$. Degradation of the superconductor critical parameters in time and structural characteristics, magnetic susceptibility, heat capacity and acoustic properties are studied, and current-voltage characteristics are determined.
rate research
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In the Bi cuprates, the presence of a near 1$times$5 superstructure is well known. Usually, this superstructure is suppressed by the substitution of lead, but there have been reports of a phase separation in so called {alpha} and {beta} phases. This paper shows in high detail time how and why the phase separation develops and what happens to the quasi-1$times$5 superstructure upon lead substitution. For this purpose, the lanthanum- and lead-substituted single-layered superconductor Bi$_{2+z}$Sr$_{2-z}$CuO$_{6+delta}$ has been investigated by scanning tunneling microscopy and low-energy electron diffraction. The La content was kept constant at slightly under-doped concentration while the Pb content was changed systematically. Thermodynamic considerations show that a phase mixture of {alpha} and {beta} phases is inevitable.
We report the fabrication of high Tc superconducting wires by photodoping a GdBa2Cu3O{6.5} thin film. An optical near-field probe was used to locally excite carriers in the system at room temperature. Trapping of the photogenerated electrons define a confining potential for the conducting holes in the CuO planes. Spatially resolved reflectance measurements show the photogenerated nanowires to be ~ 250 nm wide. Electron diffusion, before electron capture, is believed to be responsible for the observed width of the wires.
It is known that solid-state reaction in high-pressure oxygen can stabilize high-oxidation phases of Y-Ba-Cu-O superconductors in powder form. We extend this superoxygenation concept of synthesis to thin films which, due to their large surface-to-volume ratio, are more reactive thermodynamically. Epitaxial thin films of $rm{YBa_2Cu_3O_{7-delta}}$ grown by pulsed laser deposition are annealed at up to 700 atm O$_2$ and 900$^circ$C, in conjunction with Cu enrichment by solid-state diffusion. The films show clear formation of $rm{Y_2Ba_4Cu_7O_{15-delta}}$ and $rm{Y_2Ba_4Cu_8O_{16}}$ as well as regions of $rm{YBa_2Cu_5O_{9-delta}}$ and YBa$_2$Cu$_6$O$_{10-delta}$ phases, according to scanning transmission electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. Similarly annealed $rm{YBa_2Cu_3O_{7-delta}}$ powders show no phase conversion. Our results demonstrate a novel route of synthesis towards discovering more complex phases of cuprates and other superconducting oxides.
Magneto-optical imaging and magnetization measurements were applied to investigate local formation of superconducting phase effected by a random neck synthesis in Y-Ba-Cu-O system. Polished pellets of strongly inhomogeneous ceramic samples show clearly the appearance of superconducting material in the intergrain zones of binary primary particles reacted under different conditions. Susceptibility measurements allows evaluation of superconducting critical temperature, which turned out to be close to that of optimally doped YBCO.
The reflectivity $R (omega)$ of both the $ab$ plane and the c axis of two single crystals of La$_{1.875}$Ba$_{0.125-y}$Sr$_{y}$CuO$_4$ has been measured down to 5 cm$^{-1}$, using coherent synchrotron radiation below 30 cm$^{-1}$. For $y$ = 0.085, a Josephson Plasma Resonance is detected at $T ll T_c$ = 31 K in $R_{c} (omega)$, and a far-infrared peak (FIP) appears in the optical conductivity below 50 K, where non-static charge ordering (CO) is reported by X-ray scattering. For $y$ = 0.05 ($T_c$ = 10 K), a FIP is observed in the low-temperature tetragonal phase below the ordering temperature $T_{CO}$. At 1/8 doping the peak frequency scales linearly with $T_{CO}$, confirming that the FIP is an infrared signature of CO, either static or fluctuating.
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