Room temperature Mössbauer, X-ray and IR spectral studies were carried
out for the spinel system Mn0.5Zn0.5AlxFe$_{2-x}$O4,
$0 \le x \le 1$, prepared using the usual ceramic technique. X-ray
patterns confirm that all samples have single phase cubic spinel structure.
The Mössbauer spectra of the samples show a six-line magnetic pattern
and a central paramagnetic phase. They are assigned to two magnetic
subpatterns and two quadrupole doublets due to Fe3+ ions at the
tetrahedral A-sites and octahedral B-sites. The effect of increasing the
Al3+ content x on the hyperfine interaction parameters is studied and
discussed. The lattice constant, oxygen positional parameter, mean ionic
radius of the A- and B-sites, bond lengths, edges and interionic distance
are affected by the additional process x. They are determined and discussed
as functions of x. The IR spectra shows six absorption bands in the range
222–1033 cm−1. The bands are attributed to the corresponding
metal-oxygen complexes in the A- and B-sites. The hyperfine interaction
parameters, the IR band positions and intensities reveal their dependence on
the Fe3+−O2− bond length and the interionic distance at A- and
B-sites. The variation of the quadrupole doublet splitting for the B-site
and the oxygen parameter reveal the increasing trigonal distortion of the
B-site oxygen coordination. The IR absorption at 222 cm−1, the
velocity of the infrared waves when passed through the samples and the jump
rate of the lattice vacancies were found to decrease.