Charge and orbital ordering in Na0.5CoO2

Abstract: The ground state of Na0.5CoO2 has been calculated using the full potential local orbital method and local density approximation plus Hubbard (); the results demonstrate that charge and orbital ordering evidently exist in the present system in association with the antiferromagnetic state. Notable structural features observed between 300 and 30 K have been carefully examined using in situ TEM investigations, a superstructure with a wave vector of , becoming commonly visible below , can be interpreted as the charge/orbital ordering on the Co1 and Co2 sites. Moreover, we have also observed another notable superstructure with below the phase transition of , which suggests a more complicated orbital ordered state existing at lower temperatures. [Copyright &y& Elsevier]