Preparation and Superconducting Properties of Sintered Compacts of NbN Microcrystallites.
HARVARD UNIV CAMBRIDGE MASS DIV OF ENGINEERING AND APPLIED PHYSICS
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An experimental research program was undertaken to evaluate the potential of high densities of tiny voids as flux pinning sites in bulk type 2 superconductors. A review of flux pinning suggested that strong pinning forces might result if the sizes of the voids and the distances between them were somewhat larger than the Ginzburg-Landau coherence length typically 100 A but somewhat smaller than the Ginzburg-Landau penetration depth typically 2000 A. To prepare a material containing such microscopic voids, a powder metallurgical approach was adopted. A technique known as spray-drying was used to produce a finely divided powder. That powder was converted chemically into powders with the nominal compositions of niobium carbide and niobium nitride. Compositional corrections were made in the compacted powders during the sintering stage in order to maximize their superconducting transition temperatures. These corrections were accomplished more easily for the nitride than for the carbide so attention was focused on this compound during subsequent experiments.
- Ceramics, Refractories and Glass
- Solid State Physics