Oxygen Vacancy Ordering in the Double-layered Ruddlesden−Popper Cobaltite Sm2BaCo2O7−δ

Gillie, Lisa .J., Hadermann, J., Hervieu, M., Maignan, Antoine and Martin, Christine (2008) Oxygen Vacancy Ordering in the Double-layered Ruddlesden−Popper Cobaltite Sm2BaCo2O7−δ. Chemistry of Materials, 20 (19). pp. 6231-6237. ISSN 0897-4756

Abstract

A new oxygen-deficient Ruddlesden−Popper (RP) cobaltite Sm2BaCo2O7−δ (δ ≈ 1.0) has been synthesized and the crystal structure elucidated by Rietveld analysis of X-ray powder diffraction (XRD) data and transmission electron microscopy (TEM). The phase crystallizes in a primitive orthorhombic unit cell, with lattice parameters a = 5.4371(4) Å; b = 5.4405(4) Å and c = 19.8629(6) Å, and space group Pnnm. Contrary to other oxygen-deficient cobalt RP phases, the oxygen vacancies are located in the equatorial positions of the [CoO] layers to give an intralayer structure similar to Sr2Mn2O5, which is not usually observed for cobalt-containing materials. The Sm3+ and Ba2+ cations show a strong preference for distinct sites, with the majority of the larger Ba2+ cations situated in the perovskite block layers and Sm3+ cations predominantly in the rock salt layers. Magnetic susceptibility data demonstrate the strong antiferromagnetic (AFM) character of Sm2BaCo2O7−δ.

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