On the mechanism of thickness dependence of the critical current density in HTS cuprate epitaxial films

• Published in: Journal of physics. Conference series 2008-02, Vol.97 (1), p.012259
• Main Authors: Cherpak, Yu V, Svetchnikov, V L, Semenov, A V, Moskaliuk, V O, Tretiatchenko, C G, Flis, V S, Pan, V M
• Format: Article
• Language: English
• Subjects: Critical current density; Cuprates; Dislocation density; Dislocation mobility; Dislocation pinning; Electron backscatter diffraction; Epitaxial growth; Film thickness; High resolution electron microscopy; Nanoparticles; Nanostructure; Physics; Polygonization; Pulsed laser deposition; Pulsed lasers; Thin films
• ISSN: 1742-6596; 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/97/1/012259

The critical current density, Jc, in epitaxial HTS YBCO films strongly depends on the film thickness, degrading from 7-8 MA/cm2 in very thin films (50-70 nm) to less than 1 MA/cm2 in much thicker ones. Electron backscattering diffraction and high-resolution transmission electron microscopy reveal that the nanostructure of pulsed laser deposited epitaxial HTS YBCO films is evolving during growth due to high dislocation mobility. An analysis of existing pinning models leads to a conclusion that any other pinning centres but dislocations can not provide observed Jc. Extended linear defects provide a maximum elementary pinning force, if vortices are parallel to dislocation lines, while randomly distributed nanoparticles produce much lower pinning. Thus, the thickness dependence of Jc is determined mainly by the evolution of dislocation structure. Embedding of nanoparticles into HTS cuprates films results in Jc enhancement if extra dislocations are being formed during growth, preserving a high density of dislocations. Nanoparticles reduce the dislocation mobility, fix the dislocation cellular nanostructure and prevent its polygonization.