Recent important advances in materials science
- Autores: C.J. Humphreys, G.A. Botton, P.D. Brown, J. Etheridge, A.F. Moodies, M.A. Peters, Y. Xin
- Localización: Boletín de la Sociedad Española de Cerámica y Vidrio, ISSN 0366-3175, Vol. 36, Nº. 2-3, 1997, págs. 100-103
- Idioma: inglés
- Enlaces
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Resumen
This paper summarises some recent advances in four key areas in Materials Science: blue light emitters, high temperature alloys, high temperature superconductors and the phase problem in diffraction. A surprising observation with blue light emitting diodes and lasers made from GaN is that the material emits intense blue light even though it has a high density of defects. We have analysed a particular type of defect and have shov^^n that it contains no dangling bonds, v^hich explains v\^hy it does not act as a recombination centre. We then consider the problem of designing a new high temperature alloy, which has good room temperature ductility, using thermodynamic calculations. NiTi can be greatly strengthened up to 600°C by the addition of Al which forms NÍ2TÍAI precipitates in the NiTi matrix. To increase the strength above 600°C a quaternary element must be added to reduce the lattice misfit between precipitates and matrix. We are using the cluster variation method to predict which elements to add, and have shown that V reduces the misfit in theory and in practice. High temperature superconductors are widely believed to be periodic structures. We have shown that in YBa2Cu307_ §, with §<0.1, there is a structural perturbation on the scale of the superconducting coherence length Finally, recent work on the well-known «phase problem» in crystallography is reported. We have shown that phases may be directly and uniquely obtained from three beam convergent-beam electron diffraction patterns.
