Crystal growth and physical properties of Sr₄Co₃O_7.5+xCl₂ single crystals (x ~ 0.14)

We report on the single crystal growth and physical properties of the triple-layer cobalt oxychloride Sr₄ Co₃ O_7.5+x Cl₂ (x ~ 0.14) with 4-3-10 Ruddlesden–Popper type structure that was synthesized by a KCl-SrCl₂ flux method. The crystal structure was determined by means of single crystal X-ray diffraction. In this quasi two dimensional (2D) material two pyramidal CoO₅ layers and a central Co oxide layer with random oxygen deficiencies are forming the layered Co oxide blocks. These blocks are separated by Cl⁻-ions which are interacting via Van der Waals forces, thus, enhancing the quasi 2D nature of this compound. The soft X-ray absorption spectra at the Co-L_2,3 edge and O-K edge indicate that Co ions are in high spin +3 state which is in agreement with the single crystal X-ray diffraction measurements that indicate basically pyramidal oxygen environments for the Co³⁺ ions in this compound.