In situgrowth of layered, spinel, and rockhyphen;salt LiCoO2by laser ablation deposition

摘要

A study is reported of theinsitugrowth of three distinct phases of LiCoO2by laser ablation deposition on heated substrates in an oxygen background. Films were characterized by xhyphen;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 22ndash;250thinsp;deg;C resulted in a rockhyphen;salt structure, 300ndash;450thinsp;deg;C produced a modified spinel structure (lowhyphen;temperature LiCoO2), and 680thinsp;deg;C gave a hexagonal layered structure (highhyphen;temperature LiCoO2). Growth at 500 and 550thinsp;deg;C produced mixedhyphen;phase spinel and layered LiCoO2; however, at 550thinsp;deg;C, reducing the O2pressure to 100 mTorr resulted in singlehyphen;phase highhyphen;temperature LiCoO2. In the case of the rockhyphen;salt phase, modified film stoichiometries of composition Li0.5Co1.5O2and Li0.75Co1.25O2were also produced by using ablation targets of the same composition and growing at 150thinsp;deg;C under 200 mTorr O2. Average crystal grain size for all films was found to increase with growth temperature. Ordering of the cations in rockhyphen;salt films by heating was unsuccessful. thinsp;