On the cation distribution in Ni1-xCuxFe2-yAlyO4 spinels

Two spinel solid solution series, Ni1-xCuxFe2-yAlyO4 with y = 0.6 and 1.0, where 0.0 less than or equal to x less than or equal to 1.0 have been inves tigated by x-ray diffractometry and Mossbauer spectroscopy. Lattice, hyperf ine parameters, and cation distribution among the two distinct crystallogra phic sites as a function of Cu2+ and Al3+ substitution are determined. Moss bauer effect (ME) spectra at 293 K for compositions with y = 0.6 consist of one sextet for A sites, and three sextets for B sites due to different fie lds at Fe nuclei. On the other hand, the ME spectra for the compounds with y = 1.0 in the ferrimagnetic state at (293 and 77 K) show only one sextet f or Fe3+ at A site giving clear evidence for a completely inverse spinel wit h Ni, Cu, and Al ions occupying B sites. ME parameters are deduced and anal yzed for all studied compounds, where the observed hyperfine fields are exp lained on the basis of the superexchange and supertransferred hyperfine int eractions. (C) 1999 American Institute of Physics. [S0021-8979(99)06701-8].