Superconducting and normal state properties of niobium-potasium chloride composites
The electrical resistivity, current-voltage characteristics, critical currents, and DC magnetic susceptibility of composites consisting of 50 ..mu..m grains of Nb randomly dispersed in a KCl medium were measured. Data were taken between 1.2K and 20K in magnetic fields from 0 to +- 5G. The resistivity and current-voltage characteristics were measured using a standard four-terminal AC technique with a voltage sensitivity of 1 to 2nV, and the magnetic susceptibility was measured using an rf SQUID magnetometer. We found that samples with rho/sub n/ < 0.1-cm had broad resistive transitions with tails and current-voltage characteristics with kinks. The critical currents of these kinks had magnetic field periodicities indicating a junction area of 60 ..mu..m/sup 2/. For 0.1..cap omega..-cm < rho/sub n/ < 10..cap omega..-cm, a foot structure appeared in the rho vs T curves above T/sub c/, and the I-V's were characterized by steps. For rho/sub n/ > 10..cap omega..-cm there was no superconducting transition. The susceptibility decreased slowly below the grain transition temperature T/sub infinity/ and even below T/sub c/ in samples which underwent resistive transitions. The shape of the resistive transitions and the kink structure in the I-V's require a phase coherent transition model to adequately describe them. However, the poor fit of the theory to our data, the existence of the voltage steps, and the changing susceptibility below the resistive transition indicate that sample disorder plays a more important role in the superconducting transition of composites than is currently accounted for by phase coherent transition theories. (JMT).
- Research Organization:
- Ohio State Univ., Columbus (USA)
- OSTI ID:
- 5264655
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360304* -- Composite Materials-- Physical Properties-- (-1987)
ALKALI METAL COMPOUNDS
CHLORIDES
CHLORINE COMPOUNDS
COMPOSITE MATERIALS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
HALIDES
HALOGEN COMPOUNDS
MAGNETIC PROPERTIES
MAGNETIC SUSCEPTIBILITY
MATERIALS
MATHEMATICAL MODELS
METALS
NIOBIUM
PHYSICAL PROPERTIES
POTASSIUM CHLORIDES
POTASSIUM COMPOUNDS
SUPERCONDUCTIVITY
SUPERCONDUCTORS
TRANSITION ELEMENTS