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

The structure of LaSr2CuTiO6.5, 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 LaSr2CuTiO6.5 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.