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 YBa2Cu3Ox, a relationship: x = 0.025 VH - 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 YBa2Cu3O6 to 503 cm-l in YBa2Cu3O7 (Fig.l).This technique also offers the possibility to follow the structural conversion Y124 into Y123 and TI2212 into TI1212 (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 Y123 and TI1212.