Effect of deformation temperature by torsion under pressure on the microstructure, texture and flux pinning of Bi2212-base materials

Ferroelectrics and Superconductors: Properties and Applications
  • M. F. Imayev
  • ,
  • R. R. Daminov
  • ,
  • D. B. Kabirova
  • ,
  • M. Reissner
  • ,
  • W. Steiner
  • ,
  • M. V. Makarova
  • ,
  • P. E. Kazin


A systematic investigation of the effect of high-temperature deformation by torsion under pressure on the microstructure and superconducting properties of Bi2212 ceramics as well as composites on its base was carried out. It has been established that degree of basal plane texture increases with deformation temperature, reaching its maximum near to incongruent melting temperature. Quantitative investigation of sizes of colonies of grains of matrix phase and particles of non superconducting phases was curried out. The analysis of mechanism of basal plane texture formation was curried out too. Deformed materials demonstrate similar and strongly non-uniform dependence of superconducting properties (Jc, Birr, 〈E〉) on deformation temperature. In composites the introduced inclusions exert noticeable contribution to the flux pinning only after deformation at low temperatures. With increasing temperature they grow and lose their efficiency. In undoped Bi2212 and composites the best superconducting properties have samples deformed near incongruent melting temperature. The non-uniform dependence of the superconducting properties on deformation temperature are explained on the basis of conception that up to four types of flux pinning centers can operate in the material: (i) introduced inclusions, (ii) intracolonial lattice defects (point defects, dislocations, stacking faults), (iii) low-angle colony boundaries, (iv) particles of secondary phases occurring at decomposition of the Bi2212 phase near melting temperature. The number of each pinning centers depends on deformation temperature. Local maxima of superconducting properties form when at least two different types of pinning centers operate. The maximum properties are formed near melting temperature due to large extent of low-angle boundaries and increased number of secondary particles occurring at peritectic melting of Bi2212 phase. © 2012 by Nova Science Publishers, Inc. All rights reserved.