  A dense phase of a post-layered perovskite Sr3Co2O6 was created by a
high-pressure and high-temperature synthetic route and quenched to ambient
conditions. The structure of Sr3Co2O6 was determined by synchrotron X-ray
powder diffraction. Sr3Co2O6 crystallizes in the K4CdCl6-type structure (an
infinite chain-type structure), which is 6% denser than the known,
iso-compositional layered perovskite Sr3Co2O7-d (d~1). The K4CdCl6-type
Sr3Co2O6 shows complex magnetic behavior reflecting the spin-chain nature as
well as the analogue oxides Ca3Co2O6 and Ca3CoRhO6, whose microscopic magnetic
origin is still highly debated.
