Interfaces between solution-derived LiMn 2 O 4 thin films and MgO and Au/MgO substrates
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Xiuliang Ma Engineering Research Institute, University of Tokyo 2-11-16, Yayoi, Bunkyo-ku 113-8656, Tokyo, Japan
Yuji Iwamoto Japan Fine Ceramics Center, 2-4-1 Mutsuno, Atsuta-ku, 456-8587, Nagoya, Japan
Yuichi Ikuhara Engineering Research Institute, University of Tokyo 2-11-16, Yayoi, Bunkyo-ku 113-8656, Tokyo, Japan
Koichi Kikuta and Shin-ichi Hirano Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, 464-8603, Nagoya, Japan (Received 19 August 2001; accepted 16 November 2001)
Spinel LiMn2O4 thin films have been prepared on MgO(110) and Au/MgO(110) substrates by a chemical solution deposition method. The interfaces between film and substrate were characterized by means of high-resolution transmission electron microscopy (HREM) as well as x-ray diffraction. Cross-sectional HREM observation revealed that LiMn2O4 films grew epitaxially on the MgO(110) and Au/MgO(110) substrates. In the LiMn2O4 /MgO system, misfit dislocations formed to accommodate the lattice strain at the LiMn2O4 /MgO interface. In the LiMn2O4 /Au/MgO system, Au grew epitaxially on the MgO substrate with its surface facetted along {111} planes, probably because the surface energy of this plane is relatively low. The formation of these facets is considered to have a favorable effect on the growth of {111} planes of LiMn2O4 when deposited on the Au film.
I. INTRODUCTION
Fabrication of microbatteries for use in electronic devices is necessary to meet the increasing demand for miniaturization, especially for portable equipment. To fabricate such microbatteries, multilayer thin films are requested to serve as the microbatteries’ components. Microbatteries for portable systems must be lightweight and have a high energy density and high durability if they are to be used widely. Rechargeable lithium secondary batteries are one candidate for this application because LiMn2O4 spinel,1–11 the layered compound LiCoO2,12,13 and LiNiO214–16 possess high energy densities suitable for use as cathode materials. The structure of LiMn2O4 contains a three-dimensional interstitial network through which lithium ions can diffuse and allows reverse insertion into the Li-depleted MnO2 framework. In the LiMn2O4 spinel structure, Li ions occupy the 8a site and Mn ions the 16d site. From the fully charged state of MnO2, lithium ions diffuse through the network via 8a sites and 16c vacant sites in a zigzag manner along the 358
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J. Mater. Res., Vol. 17, No. 2, Feb 2002 Downloaded: 02 Apr 2015
(111) planes. If the intercalated (111) planes can be formed perpendicular to the substrate surface so as to maintain a high raw of lithium ion diffusion, an LiMn2O4 film is expected to be a highly efficient cathode. To date, fabrication of LiMn2O4 thin films has been attempted using techniques such as chemical processing via a solution route,11 chemical vapor deposition,17–19 various evaporation methods and sputtering.20–24 The properties of the films are thought to depend strongly on the film–substrate interface structure because
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