Sol-gel synthesis of LaAlO 3 ; Epitaxial growth of LaAlO 3 thin films on SrTiO 3 (100)
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Sol-gel synthesis of LaAlO3 ; Epitaxial growth of LaAlO3 thin films on SrTiO3 (100) Shara S. Shoup, Mariappan Paranthaman, and David B. Beach Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6100
E. D. Specht and Robert K. Williams Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6118 (Received 26 February 1996; accepted 26 September 1996)
A LaAlO3 precursor solution was prepared via an all alkoxide sol-gel route. The solution of lanthanum methoxyethoxide and aluminum methoxyethoxide in 2-methoxyethanol was prepared via ligand exchange starting from lanthanum isopropoxide and aluminum sec-butoxide and was used to make both LaAlO3 powders and films. Complete hydrolysis of the solution formed a gel that yielded well-crystallized LaAlO3 powders when fired in air at 800 ±C. A partially hydrolyzed solution was spun-cast on SrTiO3 (100) single crystal substrates. Epitaxial films of LaAlO3 were subsequently formed during pyrolysis in O2 at 800 ±C in a rapid thermal annealing furnace for a total of 8 min. The films were strongly c-axis oriented, verified by x-ray rocking curve results from the (003) plane with full-width at half-maximum (FWHM) = 0.87±, and had good in-plane texture shown by a f scan of the (202) plane with FWHM = 1.07±.
I. INTRODUCTION
Sol-gel techniques have been developed as viable methods for the fabrication of superconducting1–4 and buffer layers5–7 for several reasons. Sol-gel represents a low-cost, non-vacuum process and also presents a convenient way of coating long-length conductors and irregularly shaped substrates. Films of LaAlO3 are of particular interest as substrates and buffer layers for high-temperature superconductors. Critical current densities exceeding 106 Aycm2 at 77 K have been repeatedly observed from the superconductors YBa2 Cu3 O7 8–10 and (Tl, Bi) (Sr1.6 Ba0.4 )Ca2 Cu3 O92d 11 grown epitaxially on single-crystal layers of this material by various deposition techniques. Epitaxial films of the superconductors (Tl, Pb) (Ba, Sr)2 Ca2 Cu3 O9 12 and (Tl, Pb)Sr2 (Ca1–x Yx )Cu2 O7 13 have also been grown on LaAlO3 . The lattice mismatch between LaAlO3 and these superconductors is quite small, and LaAlO3 offers exceptional chemical stability and is possibly an excellent diffusion barrier. Our interest in LaAlO3 was to develop a sol-gel route to grow thin films and demonstrate that these films could be processed to give at least preferred orientation but preferably epitaxy. Epitaxial growth of buffer layers on textured surfaces is considered important in the development of practical conductors with high critical current densities using high-temperature superconductors.14,15 Films of LaAlO3 have been previously grown via a sol-gel technique on silicon and sapphire single crystal substrates.16 The chemistry employed in that work is different from the chemistry used here in that, while
starting from alkoxides, a chelating agent, acetylacetone, was used to obtain solutio
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