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Electronic structure calculations to determine the effects of impurities on ceramic properties

Elsevier Science & Technology
DOI: 10.1016/s0065-3276(00)37018-6
  • Ceranics
  • Si3N4
  • Sic
  • Corrosion
  • Flux Pinning
  • Physics


Abstract We report electronic structure calculation results for two types of ceramics with impurities. First, we studied Si3N4 and SiC, and the results show that these materials have valence states composed mainly of N sp or C sp atomic orbitals and conduction states consisting mainly of Si sp atomic orbitals. The component atoms C and N have negative net charges, whereas Si atoms have a positive net charge. The orbital mixing between the d orbitals of the ion-implanted Fe, Mo and Hf and the sp orbitals of N or C and Si causes charge transfer between these atoms. The reduced ionicity of Si weakens the attack on ceramics by ionic atoms and improves the resistance of the ceramics to corrosion. In the second part of this work, we studied Cu oxide superconductors. At present, these Cu oxides do not have sufficient critical current density at 77 K in an applied magnetic field. In order to enhance the critical current density, it is necessary to introduce pinning centers for magnetic flux lines. In the case of impurities whose atomic orbitals contribute little to HOMO (highest occupied molecular orbital), most charge carriers cannot enter the impurity sites. Thus, the superconducting order parameter becomes small or vanishes, and such impurities are effective pinning centers.

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