Synthesis and Structure of LaSr2CuTiO6.5: A New Oxygen-Deficient Ruddlesden-Popper Phase

Chem. Mater., 8 (12), 2792 -2798, 1996. cm960279b S0897-4756(96)00279-7

Synthesis and Structure of LaSr₂CuTiO_6.5: A New Oxygen-Deficient Ruddlesden-Popper Phase

Gregory M. Sarjeant, Kevin B. Greenwood, and Kenneth R. Poeppelmeier*

Department of Chemistry and the Science and Technology Center for Superconductivity, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113

Hong Zhang, Paul A. Salvador, Thomas O. Mason, and Laurence D. Marks

Department of Materials Science and Engineering and the Science and Technology Center for Superconductivity, 2137 Sheridan Road, Evanston, Illinois 60208-3108

Received May 14, 1996

Abstract:

The structure of LaSr₂CuTiO_6.5, a novel (ABO₃)_nAO n = 2 Ruddlesden-Popper phase, has been solved by powder X-ray diffraction and electron microscopy. The diffraction patterns are consistent with I4/mmm symmetry, with tetragonal lattice parameters a = 3.8816(1) Å and c = 20.296(2) Å. The structure of LaSr₂CuTiO_6.5 is similar to Sr₃Ti₂O₇, with copper and titanium disordered over the single B-cation site, and lanthanum and strontium almost perfectly disordered over the two A-cation sites. The oxygen content, determined by thermogravimetric reduction to be 6.5 (±0.1), is consistent with divalent copper with the oxygen vacancies distributed within the perovskite layers. The absence of local order and strategies for inducing a layered arrangement of the B-cations are discussed.

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