The influence of Pt and SrTiO 3 interlayers on the microstructure of PbTiO 3 thin films deposited by laser ablation on (
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The influence of Pt and SrTiO3 interlayers on the microstructure of PbTiO3 thin films deposited by laser ablation on (001) MgO S. Stemmer and S. K. Streiffer Max-Planck-Institut flir Metallforschung, Institutfiir Werkstoffwissenschaft, Seestrafie 92, 70174 Stuttgart, Germany
W-Y. Hsu Department of Materials Science and Engineering, Bard Hall, Cornell University, Ithaca, New York 14853-1510
F. Ernst Max-Planck-Institut fur Metallforschung, Institutfiir Werkstoffwissenschaft, Seestrafie 92, 70174 Stuttgart, Germany
R. Raj Department of Materials Science and Engineering, Bard Hall, Cornell University, Ithaca, New York 14853-1510
M. Riihle Max-Planck-Institut fur Metallforschung, Institutfiir Werkstoffwissenschaft, Seestrafie 92, 70174 Stuttgart, Germany (Received 23 December 1993; accepted 16 December 1994)
We have used conventional and high-resolution transmission electron microscopy to investigate the microstructure of epitaxial, ferroelectric PbTiO3 films grown by pulsed laser ablation on (001) MgO single crystals, and on MgO covered with epitaxial Pt or SrTiO3. Pronounced variations are found in the widths and lengths of a-axis-oriented domains in these films, although the volume fraction of a-axis-oriented material varies only weakly for the different types of samples. In addition, the films deposited onto Pt-coated MgO have a larger grain size than those deposited onto bare MgO or SrTiO 3 /MgO. Possible reasons for the variations in the distribution of a-axis-oriented material in these samples include differences in the elastic properties and electrical conductivities of the different substrate combinations. Because of their ferroelectric, piezoelectric, and nonlinear optical properties, epitaxial PbTiO3 thin films are potential candidates for various applications. Films of this material are typically grown at temperatures in the range of 600 °C, where PbTiO3 has a cubic, nonferroelectric perovskite structure. Upon crossing the Curie temperature of approximately 470 °C during cooling after deposition, the PbTiO3 becomes ferroelectric, and its cubic unit cell transforms to a tetragonal one with a relatively large c/a ratio of 1.065 at room temperature. As the spontaneous electric polarization is aligned with the longer c-axis of the tetragonal unit cell and the dielectric constant is smallest in this direction, c-axisoriented films are necessary for many applications of PbTiO 3 . However, it is generally found that some small volume fraction of the film has its c-axis in the plane of the substrate, which can lead to a degradation in film properties.1 Various substrates and deposition methods have been used for the growth of PbTiO3.2~6 We have chosen MgO J. Mater. Res., Vol. 10, No. 4, Apr 1995
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as a substrate material because it has the advantage that it has a low optical loss and low refractive index in the visible region, and is comparable with semiconductor systems where epitaxial MgO films have been deposited and proved to be suitable for PbTiO3 gro
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