Relationships between crystal structure and magneto-transport properties in CMR thin film of lacunar Lanthanum manganite before and after annealing

La0.8MnO3-delta epitaxial thin films have been deposited by Injection-MOCVD on MgO. As-deposited film has a semiconducting-metal and para-ferromagneti c transition at about 220 K, after annealing under air for 3 h at 700 degre esC, this transition temperature is about 310K. The crystal structure of th e film has been studied by XRD and TEM, before and after annealing. XR data collections have been recorded from an 1 mm(2) thin film piece, using a co nventional 4-circles-diffractometer designed for single crystals. In both c ases the apparent symmetry is cubic with a cell parameter twice that of the classical perovskite. In fact. the true crystal structure is monoclinic wi th microdomain twinning. Atomic positions of all the atoms have been determ ined. Improvement of the magneto-transport properties after annealing is du e to strengthening of the magnetic exchange interactions (Mn-O-Mn angles ch ange from about 165 degrees to 176 degrees) and to increasing of the Mn4+/M n3+ ratio. (C) 2001 Elsevier Science B.V. All rights reserved.