Microstructure of superconductor bulk materials and thin films

Abstract

The microstructure of single crystals of Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O prepared by different methods were studied by various physical techniques, in particular by Raman microspectroscopy. Correlations have been established between Raman spectra and structure, allowing the determination of crystalline geometry of the material versus the composition and the preparation parameters. For YBa 2 Cu 3 O x , a relationship: x = 0.025 V H - 5.57 is proposed and permits to evaluate the oxygen content by measuring simply in ZZ scattering geometry the Cu-O stretching mode V'H along the c axis of the crystal. This frequency varies from 465 cm -1 in YBa 2 Cu 3 O 6 to 503 cm -l in YBa 2 Cu 3 O 7 (Fig.l). This technique also offers the possibility to follow the structural conversion Y 124 into Y 123 and TI 2212 into TI 1212 (Fig.2) by appropriate thermal treatment. The preferentiel departure of the “CuO” or “TIO” chain/layer (Fig.3) is explained by weaker interaction forces between these layers and the adjacent ones, compared to those between the remaining layers. This helps to predict the localization of an eventual intercation in Y 123 and TI 1212 .