Autor: Lawrence V. Hmurcik, A. Bidarian, B. Ibarra, L.D. Matthews
Rok vydání: 1998
Předmět:
Zdroj: Journal of Materials Science. 33:5653-5659
ISSN: 0022-2461
Popis: It is well known that conduction in YBa2Cu3O7 (YBCO) is by means of copper “planes” and “chains,” where planes and chains describe the degree of bonding between copper and oxygen. Changes of conductivity versus temperature have been used to show that conduction in YBCO in the normal state is 3-dimensional, while conduction approaching the onset of the superconducting state is first 2-dimensional and then 3-dimensional. We have found another method to monitor this 2-to-3 transition. Using square samples, and measuring the voltage at each corner caused by a current applied to the opposite corners, one can find the conductivities along the x-axis and the y-axis. The ratio of these conductivities is unity for homogeneous samples in the normal state. However, in transition to the superconducting state, the ratio of conductivities changes. We examine this change as a function of sample purity, sample history, and exposure to an external magnetic field. Our data are consistent with data reported in the literature, and they suggest the existence of another state change deep in the superconducting state, which is only observable with the application of a magnetic field. Measurements were also carried out to correlate the anisotropy with sample porosity. Measurements of normal state resistivity, critical temperature, and critical current characterize the sample's porosity, and these data affect the anisotropy in the superconducting state in a manner directly proportional to the porosity.
Databáze: OpenAIRE
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