Effect of Film Thickness and Crystal Orientation on the Constituent Phase in Epitaxial BiFeO3–BiCoO3 Films Grown on SrTiO3 Substrates

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The crystal symmetries of epitaxial ($1-x$)BiFeO3–$x$BiCoO3 films ($x=0--0.46$) grown on (100)SrTiO3, (110)SrTiO3, and (111)SrTiO3 substrates covered with/without SrRuO3 layers were systematically investigated as a function of film thickness and the crystal orientation of the substrates. Raman analysis was an effective method of crystal symmetry research on epitaxial BiFeO3–BiCoO3 films. Crystal symmetry was changed from being rhombohedral to tetragonal through the mixture of these symmetries with increasing BiCoO3 content irrespective of film thickness and the crystal orientation. However, the constituent phase was strongly depended on film and the crystal orientation of the substrates. The perovskite single phase was observed up to a higher $x$ for the films grown on (100)SrTiO3 substrates than for those grown on (110)SrTiO3 and (111)SrTiO3 substrates. On the other hand, the constituent phase of the films grown on (111)SrTiO3 substrates was similar to that of the strain free powders obtained by high-pressure synthesis.
2010-09-25