X-ray diffraction line broadening effects in MBa2Cu3O7−δ (M = Y, Gd) thin films

Abstract

X-ray diffraction line profile analysis (LPA) has been carried out on a set of superconducting thin films of MBa2Cu3O7−δ (MBCO, M = Y, Gd), deposited by pulsed and continuous physical vapor deposition (PVD) techniques on different single-crystal substrates. The choice of appropriate deposition conditions, substrates, and buffer layers promoted a high degree of [00l] preferred orientation, leading to a well-defined columnar grain morphology in the MBCO films. Under such conditions, the LPA of diffraction patterns, collected with the widely spread Bragg–Brentano geometry, gives detailed information on the distributions of coherent scattering domain (crystallite) size and microstrain along the [00l] growth direction; considering the particular MBCO film microstructure, the mean crystallite size () can be regarded as the mean distance between extended planar defects parallel to the film surface. The significance of goes beyond a merely statistical value. As long as the morphology of the films is similar, is found to be strictly connected with the average microstrain by a simple proportionality relation. Moreover, the correlation extends to important superconducting transport parameters, like the transition width ΔTc. These regular behaviors are irrespective of deposition techniques, substrate, and film materials, and are a clear indication of some fundamental relation between the defects and the overall properties of the films.