Evidence for charge-density-wave nature of the charge-ordered phase in La1/3Sr2/3FeO3

We have investigated the threefold-charge ordering in La1/3Sr2/3FeO3 sample below T-CO similar to 200 K. We have measured superlattice reflections, q=a(*)(1/3 1/3 1/3), using the resonant x-ray scattering technique. The nonresonant intensities are consistent with a periodic structural modulation of both Fe and Sr(La)O-3 atomic planes. These displacements give rise to two nonequivalent Fe sites in the ratio of 2:1. Strong resonances are observed at the Fe K edge in the sigma-sigma(') geometry. These resonances did not exhibit azimuthal dependence. A charge disproportionation of 0.6 electrons is determined between the two Fe sites. Hence, the charge-ordered phase can be better understood as a charge-density-wave with a ...Fe3.3+Fe3.9+Fe3.9+... sequence along the cubic [111] direction.