Nonstoichiometric Li-pseudobrookite(ss) in the Li2O-Fe2O3-TiO2 system

Phase equilibria in the Li2O-Fe2O3-TiO2 system were studied at 900 and 1000 degrees C using the quenching method. Two new ternary solid solutions, based on the pseudobrookite and ramsdellite structure types, were Identified and structurally characterised using Rietveld refinements of powder X-rag data, The pseudobrookite(ss) showed deviations from M3O5 stoichiometry towards metal-rich compositions which increased with increasing substitution of Li+Ti for Fe, from Fe2TiO5 to Li0.81Fe0.27Ti2.09O5 (=M3.17O5) A neutron diffraction refinement was made on Li0.81Fe0.27Ti2.09O5, space group Ccmm, with a = 9.6576(2), b = 3.7532(1), c = 9.8820(2) Angstrom. Titanium is ordered in the eightfold MZ site while lithium, together with minor iron and titanium, is ordered in the four-fold M1 site. The excess lithium (0.17 Li per formula unit) was located in interstitial sites in the structure, having square-pyramidal coordination. A local-ordering model is presented which involves Li-3 clusters with Li-Li = 2.3 Angstrom. (C) 1998 Academic Press.