X-ray diffraction study on Li@@d@@ix@@CoO@@d2@ below ambient temperature

In order to elucidate the structural change of Li@@d@@ix@@CoO@@d2@ with temperature (@@iT@), powder X- ray diffraction measurements have been carried out using a synchrotron radiation source in the @@iT@ range between 300 and 90 K for the samples with @@ix@=1.02, 0.60, 0.56, and 0.53. The samples with @@ix@ < 1.02 were prepared by an electrochemical reaction in a non-aqueous lithium cell. The @@ix@=1.02 and 0.60 samples are in a rhombohedral phase ([View the MathML source]) in the whole @@iT@ range measured. On the other hand, the @@ix@=0.56 and 0.53 samples exhibit a structural transition around 140 K, although the both samples are in a monoclinic phase (@@iC@2/@@im@) down to 90 K. That is, the angle between @@ia@@@dM@- and @@ic@@@dM@-axis (@@ib@@@dM@) increases monotonically down to 150 K, then increases more rapidly with further lowering @@iT@. The values of [View the MathML source] and @@ia@@@dM@/@@ib@@@dM@, which are parameters to characterize a monoclinic distortion from the hexagonal symmetry, are [View the MathML source] and @@ia@@@dM@/@@ib@@@dM@ < 1.732 above 140 K, while [View the MathML source] and @@ia@@@dM@/@@ib@@@dM@[asymptotic to]1.732 below 140 K. This suggests that the monoclinic distortion below 140 K is mainly caused by a gliding along the basal plane.