Short-range charge ordering in Ho0.1 Sr0.9 Co O3-x (0.15≤x≤0.49)

We report the observation of Co3+ Co4+ short-range charge ordering in 10% Ho-doped SrCo O3-x by means of high resolution neutron powder diffraction. The associated one-dimensional commensurate modulation, which can be described with the propagation vector qCO = (0 0 1 2) with respect to the cubic perovskite cell Pm3m, occurs for compositions close to x=0.20, corresponding to a 1:1 Co3+ Co4+ ratio and extends over clusters of finite size (D∼250 Å). The bond valence sums for the Co3+ and Co4+ sites are +3.07 (7) and +3.95 (11) (x=0.19), very close to their nominal values +3 and +4. We attribute this astonishing observation to the one-dimensional (1D) character of the associated distortion pattern, whose elastic stabilization is eased with respect to the 3D arrays reported for other charge-ordered perovskite oxides.