Sr₅V_1.5Fe_3.5O₁₅: A Transition-Metal-Ordered Perovskite with 5-Fold Superstructure along [111]_pc Direction

Many cation-ordered perovskites have been reported, exploiting differences in cation size and valence. They are mostly double perovskite structures with rock-salt ordering, while cation ordering with periodicity longer than three primitive perovskite cells is relatively rare. Here, we successfully synthesized a 5-fold cation-ordered perovskite oxide, Sr₅V_1.5Fe_3.5O₁₅, through topochemical oxidation of oxygen-deficient perovskite Sr₅V_1.5Fe_3.5O₁₄. The cation ordering in the precursor, with 5-fold periodicity of triple 100% Fe layers and double 75% V and 25% Fe layers along the [111] direction of the primitive perovskite cell, is preserved during topochemical oxidation, as evidenced by synchrotron and neutron diffraction analyses. Mössbauer spectroscopy measurements for Sr₅V_1.5Fe_3.5O₁₅ suggest a sign of charge ordering to Fe³⁺ and Fe⁴⁺ below ∼50 K, where a short-range order is a plausible picture due to the existence of the iron-poor double layers.