Publication
Complex AC conductance of YBaCuO films
Résumé
The AC linear response of YBaCuO films prepared by RF magnetron sputtering to a small oscillating field was studied as a function of temperature and transverse magnetic field. The structures observed are quite similar to those found in artificially prepared two-dimensional periodic junction arrays where the transition from a phase-ordered to a phase-disordered state at Tc is attributed to the vortex unbinding mechanism predicted by the Kosterlitz-Thouless theory for phase transitions in two dimensions. The magnetic field data suggest that the typical cell size of the YBCO array is a few μm, on the order of the grain size. This suggests that the ceramic films can be modeled as two-dimensional networks of Josephson tunnel junctions, the junctions being located at the grain boundaries.
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Proximité ontologique
Concepts associés (32)
Transition de phase
vignette|droite|Noms exclusifs des transitions de phase en thermodynamique. En physique, une transition de phase est la transformation physique d'un système d'une phase vers une autre, induite par la variation d'un paramètre de contrôle externe (température, champ magnétique...). Une telle transition se produit lorsque ce paramètre externe atteint une valeur seuil (ou valeur « critique »). La transformation traduit généralement un changement des propriétés de symétrie du système.
Joint de grains
Un joint de grains est l'interface entre deux cristaux de même structure cristalline et de même composition, mais d’orientation différente. vignette|Microstructure de VT22 () après trempe. L'échelle est en micromètres. vignette|Schéma d'un joint de grain, dont les atomes communs à deux cristaux (orange et bleu) sont représentés en vert. Les joints de grains peuvent se former dans deux cas de figure : lors de la solidification du matériau et par recristallisation, durant certains traitements thermomécaniques.
Abnormal grain growth
Abnormal or discontinuous grain growth, also referred to as exaggerated or secondary recrystallisation grain growth, is a grain growth phenomenon through which certain energetically favorable grains (crystallites) grow rapidly in a matrix of finer grains resulting in a bimodal grain size distribution. In ceramic materials this phenomenon can result in the formation of elongated prismatic, acicular (needle-like) grains in a densified matrix with implications for improved fracture toughness through the impedance of crack propagation.
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