Epitaxial Growth of Strontium Bismuth Tantalate/Niobate on Buffered Magnesium Oxide Substrates
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0902-T03-46.1
Epitaxial Growth of Strontium Bismuth Tantalate/Niobate on Buffered Magnesium Oxide Substrates George H. Thomas,1 Jonathan S. Morrell,2 Tolga Aytug, Ziling B. Xue1 and David B. Beach Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6119, USA 1 Deparment of Chemistry, University of Tennessee, Knoxville TN 37919 USA 2 Y-12 National Security Complex, Oak Ridge, TN 37831 USA ABSTRACT Epitaxial films of strontium bismuth tantalate (SrBi2Ta2O9, SBT) and strontium bismuth niobate (SrBi2Nb2O9, SBN) were grown using solution deposition techniques on magnesium oxide (MgO) substrates buffered with a 100 nm layer of lanthanum manganate (LaMnO3, LMO). Film structure and texture analyses were carried out using x-ray diffraction. Theta-2theta diffraction patterns were consistent with a c-axis aligned structure for both the buffer layer and the solution deposited films. Theta-2 theta scans revealed (001) SBT, SBN //(001) LMO epitaxial relationships between the solution deposited films and the buffer layer. A pole figure about the SBT, SBN (115) reflection indicated a single in-plane epitaxy. Film quality was assessed using T and N scans. Nuclear Magnetic Resonance (13C) was used to characterized the methoxyethoxide solutions used for the deposition of the SBN and SBT films. INTRODUCTION Layered perovskites containing bismuth were first discovered by Aurivillius [1] and possess interesting electrical properties, including fatigue free dielectric behavior in non-volatile memory applications.[2] They have the general composition Bi2An-1BnO3n+3 (n = 1 to 3) and have two structural layers consisting of a (Bi2O2)2+ layer between a double defect perovskite layer of the general form (An-1BnO3n+1)2-. The “A” site is partially occupied by a large, dodecahedrally coordinated ion such as Ca2+, Sr2+, Mg2+, Ba2+, Pb2+, Bi3+ or a rare earth ion, while the “B” site is occupied by an octahedrally coordinated site such as Ga 3+, Al3+, Ti4+, Ta5+ or Nb5+. [3] While considerable work has been done on the electrical properties of these materials, relatively little attention has been paid to their optical properties. The perovskite layer is chemically and structurally similar to the tungsten bronze structured compounds such as SrNb2O6 [4] which have a very large linear electro-optic (Pockels) effect. Of particular interest would be epitaxial films of these materials due to the reduction in light scattering at grain boundaries, the anisotropy of the dielectric effect, and the ability to integrate these materials into highly efficient and compact electro-optic modulators. Our initial effort are aimed at producing an efficient waveguide so that the electro-optical properties of these materials may be studied in thin-film form. To this end, we have attempted to epitaxially deposit SBT and SBN on magnesium oxide (MgO) single crystals. Magnesium oxide was chosen because of the difference in refractive index between MgO (1.7) and SBT and SBN (~2.4). Direct growth of SBN on MgO has been reported using laser ablation.
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