Structure and Oxygen Stoichiometry in Sr 3Co 2O 7- y (0.94 ≤ y ≤ 1.22)

Abstract

A new, oxygen-deficient Ruddlesden-Popper phase, Sr 3Co 2 O 7- y (0.94 ≤ y ≤ 1.22) has been prepared and its structural characterization has been achieved by the Rietveld refinement of powder X-ray and powder neutron diffraction data. At low y the system is tetragonal but as y increases a phase change to orthorhombic occurs. Sr 3Co 2O 6.06 crystallizes in the space group I4/ mmm, adopting the Sr 3Ti 2O 7 type structure, but with the oxygen vacancies lying exclusively on the site linking the CoO 6 octahedra. This leads to an unusual square-pyramidal coordination for Co(III). The orthorhombic structures of the samples y = 1.22 and y = 1.06 have been determined using powder neutron diffraction. Crystallizing in the space group Immm, the ordering of oxygen vacancies in the Ruddlesden-Popper phase, leads to a threefold tripling along the b-axis direction.