A MOSSBAUER AND X-RAY-DIFFRACTION INVESTIGATION OF LI-TI FERRITES

Li0.5+0.5xTixFe2.5-1.5xO4, x less-than-or-equal-to 0.7, has been investigated using x-ray powder diffraction (17-70-degrees 2theta) and Mossbauer spectroscopy (300 and 77 K). All compositions show single cubic spinel structure with a constant lattice parameter of 0.833 nm. The room temperature Mossbauer spectra gave magnetic sextets which broadened with increasing x; in addition, a small paramagnetic component started to develop for higher Ti substitution. The 77 K measurements are less broadened, but the intensity of the central doublet has not changed. The Zeeman patterns were fitted with two models: two six-line Lorentzian subspectra assigned to the tetrahedral and octahedral sites and a distribution of magnetic hyperfine fields. The hyperfine fields at both temperatures for the A and B sites decrease as x increases, but at a faster rate for the former site when x > 0.3. Similar distribution profiles have been deduced using the latter model. An asymmetric distribution is observed for x less-than-or-equal-to 0.4, with the hyperfine fields derived from the Lorentzian fit falling inside the distribution. As x increases a peak at lower hyperfine fields develops and becomes more prominent as x increases. The influence of Li and Ti substitution on the hyperfine field is discussed.