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

In this work some members of the La2-xSrxCu1-x/2Tix/2O4-delta and La2-xSrxCu0.5Ti0.5O4-delta families have been synthesised in the composition ranges 0.1 less than or equal to x less than or equal to 1.5 and 1.0 less than or equal to x less than or equal to 1.5, respectively. A complete solid solution between La2CuO4 and Sr2TiO4, 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 LaSrCu0.5Ti0.5O4-delta and La1.9Sr0.1Cu0.95Ti0.05O4-delta 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 less than or equal to 0.2).