Orientation change with substrate type and composition in (100)/(001)-oriented epitaxial tetragonal Pb(Zr_xTi_1−x)O₃ films

Abstract

Tetragonal 30-nm thick Pb(Zr_xTi_1−x)O₃ films were grown epitaxially on (100) KTaO₃ and (100) SrTiO₃ single crystal substrates by pulsed metal organic chemical vapor deposition. High temperature X-ray diffraction (XRD) reciprocal space mapping showed that Pb(Zr_xTi_1−x)O₃ thin films of different compositions have a misfit strain that may not be apparent from room temperature XRD measurements. The misfit strain depends on the combination of the substrate and film composition. The misfit strain revealed by high temperature XRD measurements showed good agreement with previous theoretical predictions, even for relaxed films had except for an anomalous Pb(Zr_0.45Ti_0.55)O₃ film, perfect (100) orientation was obtained for PbTiO₃ on (100)-KTaO₃ substrates with in-plane tensile and compressive strain. A mixture of (100) and (001) orientations was found for Pb(Zr_xTi_1−x)O₃ thin films with x = 0.22 and 0.30. On (100)-SrTiO₃ substrates, however, the (001) orientation was obtained for Pb(Zr_xTi_1−x)O₃ thin films grown with x = 0–0.45. These results reveal the importance of accounting for misfit strain at the growth temperature rather than at room temperature. Anomalous Pb(Zr_0.45Ti_0.55)O₃ films grown on KTaO₃ had a perfect (001) orientation, despite having a small misfit strain at the growth temperature owing to relaxation. The lower degree of tetragonality of the crystal structure may contribute to the perfect (001) orientation in these films.