Detection of interfacial strain and phase separation in MBa ₂Cu₃O_7-x thin films using Raman spectroscopy and X-ray diffraction space mapping

Phase stoichiometry, texture, and the presence of microdomains in high quality MBa₂Cu₃O_7-x (M-123, M = Y or a rare earth metal) thin film specimens were investigated using Raman microspectroscopy methods. Complementary diffraction space mapping (DSM) measurements on the same specimens (using 17 keV X-rays from a synchrotron radiation source in symmetric and asymmetric reflection geometries) provided information on their state of epitaxy, interplanar tilt, strain, crystallite twinning, and orthorhombicity. The effects of substrate crystallography and the presence of a buffer layer on the epitaxial quality of the overlying M-123 film were also studied using DSM. A correlation between the interfacial strain present in each thin film specimen and the degree of twinning detected in the M-123 film microstructure was observed. The observed strain relief (complementing crystallite twinning) is consistent with a mechanism based on microdomain formation due to the oxygen atom reordering accompanying the transition of the tetragonal phase of MBa₂Cu₃O _7-x to the orthorhombic phase during the M-123 film deposition/oxygenation process.