New phases in the SrO–La2O3 –TiO2–CuO system with the K2NiF4 structure

Abstract

In this work some members of the La _2-x Sr _x Cu _{1- x/2} Ti _x/2 O _4-δ and La _2-x Sr _x Cu _0.5 Ti _0.5 O _4-δ families have been synthesised in the composition ranges 0.1≤x≤1.5 and 1.0≤x≤1.5, respectively. A complete solid solution between La ₂ CuO ₄ and Sr ₂ TiO ₄ , has been found by X-ray powder diffraction and no evidence of Cu/Ti ordering has been found either by these means or by electron diffraction, compositions being checked by energy dispersive analysis by X-rays (EDAX). Samples were compared before and after oxidation with BrO ^- and only materials with stoichiometries close to LaSrCu _0.5 Ti _0.5 O _4-δ and La _1.9 Sr _0.1 Cu _0.95 Ti _0.05 O _4-δ could be oxidised in these conditions. Paramagnetic susceptibilities showed the presence of small fractions of superconducting phases (T _c values close to 30 K) for samples with low titanium content (x≤0.2).