Studies of nonlinear electrodynamics of high-temperature superconductors

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1991

OSTI ID:7114749

Lam, Q H

Nonlinear electrodynamics of high-Tc superconductors are studied theoretically and experimentally. For powdered samples, a novel model is presented in which the metallographically observed superconducting grains in the powder are modeled as superconducting current loops of various areas with weak links. Surprising harmonic generation behavior in an ac field, H[sub 1] cos([omega]t), is predicted by the model; the power at high harmonics show sharp dips almost periodic in a super-posing dc magnetic field, revealing flux quantization in the prototype loops in the model. Such oscillation of the harmonic power in dc magnetic field, P[sub nf](H[sub dc]), is experimentally observed in powdered YBa[sub 2]Cu[sub 3]O[sub 7]. For bulk sintered cylindrical samples, a generalized critical state model is presented. The nonlinear electrodynamics are due to flux-pinning. Experiments in ac and dc magnetic fields on a sintered cylindrical rod of YBa[sub 2]Cu[sub 3]O[sub 7] yield unambiguous evidence of independent inter- and intragranular contributions to the complex harmonic permeability [mu][sub n] = [mu][prime][sub n] - i[mu][double prime][sub n]. These data, together with P[sub nf](H[sub dc]), are explained quantitatively by the generalized critical state model, yielding a dependence on magnetic field of J[sub c](H) [approximately] H[sup 02][sub local] for the intergranular component, a steeper field dependence than for conventional type-II superconductors. Temperature-dependence measurements reveal that, while the intragranular supercurrents disappear at T[sub c] [ge] 91.2 K, the intergranular supercurrents disappear at T [ge] 86.6 K.

• Research Organization: California Univ., Berkeley, CA (United States)
• OSTI ID: 7114749
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360207* -- Ceramics
Cermets
& Refractories-- Superconducting Properties-- (1992-)
665411 -- Basic Superconductivity Studies-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
COPPER COMPOUNDS
CUPRATES
DATA
ELECTRODYNAMICS
EXPERIMENTAL DATA
HIGH-TC SUPERCONDUCTORS
INFORMATION
MAGNETIC FLUX
NONLINEAR PROBLEMS
NUMERICAL DATA
OXYGEN COMPOUNDS
SUPERCONDUCTORS
THEORETICAL DATA
TRANSITION ELEMENT COMPOUNDS