Transmission electron microscopy and x-ray structural investigation of La 0.7 Ca 0.3 MnO 3 thin films

• Published in: Journal of materials research 1998-08, Vol.13 (8), p.2161-2169
• Main Authors: Li, Y. H., Thomas, K. A., de Silva, P. S. I. P. N., Cohen, L. F., Goyal, A., Rajeswari, M., Mathur, N. D., Blamire, M. G., Evetts, J. E., Venkatesan, T., MacManus-Driscoll, J. L.
• Format: Article
• Language: English
• ISSN: 0884-2914; 2044-5326
• DOI: 10.1557/JMR.1998.0302

The structural changes and magnetoresistance (MR) properties of as-grown and post-annealed La 0.7 Ca 0.3 MnO 3 films were investigated by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The data for the films were compared to that for bulk La 0.7 Ca 0.3 MnO 3 post-annealed under the same conditions. The main structure of the as-grown films was face-centered pseudo-cubic with a doubled perovskite unit cell, of size ∼2 a p × ∼2 a p × 2 a p , where a p is the single perovskite parameter. The phase showed a cube-on-cube epitaxy with the underlying LaAlO 3 substrate. Upon annealing to a saturation point, a minor primitive pseudo-tetragonal structure evolved, of cell parameters . A total of four possible orientations of the two structures was observed by TEM, comprised of one orientation of the ∼ 2 a p × ∼ 2 a p × ∼ 2 a p cell, i.e., the cube-on-cube epitaxy, giving rise to ( 00l ) peaks in x-ray, and three orientations of the cell, giving rise to a single ( 00l )/( hk 0) peak in x-ray. The bulk La 0.7 Ca 0.3 MnO 3 sample also contains the × structure. The difference between the bulk and the film and the effects of annealing on films can be ascribed to the influence of strain between the film and substate, induced by lattice mismatch.