A wide angle X-ray scattering (WAXS) study of nonstoichiometric nickel manganite spinels NiMn2 square O-3 delta/4(4+delta)

WAXS study of highly divided oxides obtained by low temperature decomposition of mixed oxalates NiMn2(C2O4)(3) . nH(2)O in air at low temperatures (573 and 623 K) shows that oxalate decomposition leads probably directly to the spinel structure NiMn2 rectangle(3 delta/4)O(4+delta) with a very high content of cation vacancies essentially located in tetrahedral sites. Thermogravimetric analyses confirm that these oxides have a great nonstoichiometry proportion; the higher value (delta approximate to 0.9) is observed for the compound synthesized at 573 K. (C) 1997 Academic Press.