Systematic study of the growth-temperature dependence of structural disorder and superconductivity in YBa2Cu3O7- delta thin films.

Abstract

The growth-temperature dependence of the crystal structure and superconductivity of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ thin films has been investigated quantitatively for a series of sputter-deposited films prepared at substrate temperatures ranging from 593 to 726 \ifmmode^\circ\else\textdegree\fi{}C. X-ray diffraction revealed that the reflection intensities of the films, especially I(004), I(005), and I(006), change systematically with substrate temperature. Structure analyses suggested that there is a considerable degree of disorder between Y and Ba atoms in the structure of the thin films deposited at lower substrate temperatures. This degree of disorder decreases rapidly from 14 to 3 % (percentage of the Y site substituted by Ba atoms) with increase in the substrate temperatures up to 630 \ifmmode^\circ\else\textdegree\fi{}C, and then decreases slowly to zero percent and remains zero even at higher substrate temperatures. Electrical-resistivity measurements showed that the superconducting transition temperatures of the thin films increase with increasing substrate temperature, in good agreement with the recovery of the disordered structure. The results indicate that there is an intrinsic relationship between the cation disorder and ${\mathit{T}}_{\mathit{c}}$, which are both strongly dependent on the growth temperature.