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Structure and Morphology of Epitaxially Intergrown (100)- and (116)-Oriented SrBi2Ta2O9 Ferroelectric Thin Films on SrLaGaO4(110) Substrates H. N. Lee, D. N. Zakharov, P. Reiche,1 R. Uecker,1 and D. Hesse Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle/Saale, Germany 1 Institut für Kristallzüchtung, Max-Born-Str. 2, D-12489 Berlin, Germany

ABSTRACT

SrBi2Ta2O9 (SBT) epitaxial thin films having a mix of (100) and (116) orientations have been grown on SrLaGaO4(110) by pulsed laser deposition. X-ray diffraction θ−2θ and pole figure scans, and cross-sectional transmission electron microscopy (TEM) analyses revealed the presence of two epitaxial orientations, SBT(100) || SLG(110); SBT[001] || SLG[001] and SBT(116) || SLG(110); SBT [ 1 10] || SLG[001]. By calculating the integrated intensity of certain x-ray diffraction peaks, it was established that the crystallinity and the in-plane orientation of the (100) and (116) orientation are best at a substrate temperature of 775 °C and 788 °C, respectively, and that the volume fraction of the (100) orientation at about 770 °C reached about 60%. By scanning force microscopy and cross-sectional TEM investigations we found that the a-axisoriented grains are rounded and protrude out due to the rapid growth along the [110] direction, leading to a distinct difference of the surface morphology between (100)- and (116)-oriented grains.

INTRODUCTION

Ferroelectric SrBi2Ta2O9 (SBT) belongs to the space group A21am and has an orthorhombic structure, a = 0.5531 nm, b = 0.5534 nm, and c = 2.4984 nm at room temperature [1]. The vector of the spontaneous polarization is directed along the a axis (perpendicularly to the c axis). The growth of epitaxial films which have their spontaneous polarization along the normal to the film plane, i.e., a-axis oriented films, or at least pointing out of the film plane, i.e., non-c-axis oriented films, is desirable for applications of SBT films to ferroelectric memory devices in planar capacitor geometry. In addition, due to its highly anisotropic structure, the ferroelectric properties are also anisotropic. Epitaxial SBT films with different crystallographic orientations, therefore, allow to study the dependence of their basic properties on the orientation. (100)/(010)- and (110)-oriented SBT films have been grown on (110)-oriented MgO [2] and (100)-oriented SrLaAlO4 (SLA) [3], respectively. It appears that in most cases the epitaxial growth of the SBT film and its crystallographic orientation are based on the lattice match between film and substrate. Accordingly, in order to grow a-axis-oriented films of high quality, the substrates (and their orientations) should be chosen in such a way that film-substrate lattice mismatches are as low as possible. In this study, we report the epitaxial growth of SBT films on (110)-oriented SrLaGaO4 (SLG) single crystal substrates. (110)-oriented SLG crystals (K2NiF4type tetragonal structure, a = 0.3843 nm, c = 1.268 nm [4]) provide a good lattice match for the C8.5.1

growth of (100)-oriented S