A-site deficiency, phase purity and crystal structure in lanthanum strontium ferrite powders

Lanthanum strontium ferrite (LSF) powders of average composition of (La1-xSrx)(y)FeO3+delta were fabricated over a range of average strontium composition between 0.2 <= x'<= 0.5 and average A-site occupancy between 0.8 <= y' <= 1.0. Samples that were originally determined to be perovskite phase pure using X-ray diffraction with CuK. radiation were found to have significant amounts of non-perovskite phases when evaluated using high-energy synchrotron radiation. As-fabricated samples with nominal A-site deficiency, y'< 1, contained a hexaferrite phase. When treated at 955 degrees C in pO(2) = 10(-10) atm, those samples contained magnetite. The actual composition of the perovskite phase was corrected to account for the presence of the second phases through mass balance calculations. As a result, the actual A-site deficiency of the perovskite phase was much lower than the average value of the bulk powder. For as-fabricated powders with x'<0.4, it was determined that the A-site deficient LSF perovskite phases were metastable. At equilibrium, a mixture of A-site stoichiometric perovskite and hexaferrite phases was present. The refined perovskite crystal structures and unit cell volumes were consistent with literature trends. (C) 2007 Elsevier B.V All rights reserved.