In situ growth of layered, spinel, and rock-salt LiCoO2 by laser ablation deposition
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abstract
A study is reported of the in situ growth of three distinct phases of LiCoO2 by laser ablation deposition on heated substrates in an oxygen background. Films were characterized by x-ray diffraction from which crystal structure, crystal orientation, lattice constants, and phase information were obtained. Electron microscopy was used to investigate crystal grain size and overall film morphology. For deposition under 2000 mTorr O2, substrate temperatures of 22–250 °C resulted in a rock-salt structure, 300–450 °C produced a modified spinel structure (low-temperature LiCoO2), and 680 °C gave a hexagonal layered structure (high-temperature LiCoO2). Growth at 500 and 550 °C produced mixed-phase spinel and layered LiCoO2; however, at 550 °C, reducing the O2 pressure to 100 mTorr resulted in single-phase high-temperature LiCoO2. In the case of the rock-salt phase, modified film stoichiometries of composition Li0.5Co1.5O2 and Li0.75Co1.25O2 were also produced by using ablation targets of the same composition and growing at 150 °C under 200 mTorr O2. Average crystal grain size for all films was found to increase with growth temperature. Ordering of the cations in rock-salt films by heating was unsuccessful.
