Transmission electron microscopy study of epitaxial Li-Mn-O films grown by pulsed laser deposition: The effect of temperature on formation of phases

A simple system of epitaxial film electrodes with no additives is desirable for investigation surface reactions and anisotropic electrochemical properties of battery's active materials. In this work we demonstrate the possibility of growing epitaxially by pulsed laser deposition single orientation thin films of two phases, orthorhombic o-LiMnO₂ and monoclinic m-Li₂MnO₃; the phases were and still are of great interest for developing high capacity intercalation cathodes for Li-ion batteries. Orientation of the films was controlled by selecting orientation of SrTiO₃ substrate covered coherently with a layer of SrRuO₃ to provide electrical contact for future electrochemical measurements. Different phases were formed by adjusting temperature of a substrate during deposition, 600 °C for forming m-Li₂MnO₃, and 700–800 °C – for o-LiMnO₂. Detailed high-resolution scanning transmission electron microscopy of cross-sections has determined the unique orientation relationship for both phases, which can be seen as cube-on-cube of cubic and pseudo-cubic oxygen sub-lattices of SRO and Li-Mn-O phases, respectively. Lower symmetry of the Li-Mn-O phases results in formation of structural domains, which are analyzed in detail. - Highlights: • Pulsed laser deposition of single-crystal-like Li₂MnO₃ epitaxial films on SrTiO₃ substrates. • Significant effect of deposition temperature on formation of phases. • Monoclinic Li₂MnO₃ was orthorhombic LiMnO₂ formed at 600 °C and 700–800 °C, respectively. • Both phases grew as epitaxial films. • Unique film/substrate orientation relationship and structural domains has been determined for both phases.