Spinels represent a wide range of compounds all having the
same general formula, AB2O4, where A and B are divalent
and trivalent metal cations that typically sit in tetrahedral
and octahedral holes in the oxygen lattice, respectively.
There are three classifications of the spinel structure, normal
spinel (A)tet[B2]octO4, inverse spinel (B)tet[A,B]octO4,
and random spinel (B0.6A0.33)tet[A0.6B1.33]octO4. The spinel
structure can also crystallize in either a cubic or tetragonal
form, with the tetragonal form being generated by a Jahn–
Teller deformation of the octahedral. Spinels have a wide
variety of uses, for example, they can be used, as catalysts
for oxygen evolution reaction [1–3], reduction of nitrogen
oxides, oxidation of CO, hydrocarbons [4], decomposition
of NO and hydrogenation of CO [5], as thermistors and as
infrared sensors [6].
The structure of the mixed metal spinel
(Co,Mn)(Co,Mn)2O4 is similar to a mixture of MnCo2O4
and CoMn2O4 [7, 8]. Methods used in the ceramics
industry to prepare this spinel starting from manganese and
cobalt oxide precursors require heat treatment at high
temperatures (C1172 K) and need long treatment times [9].
From this type of preparation method the powders produced
have large particle sizes and low surface areas. A
method to produce higher surface area metal oxides
involves the decomposition of precursors and subsequent
heat treatment at low temperatures. Several precursors have
been used for the preparation of the mixed metal spinel:
acetates [10], carbonates [4, 11], citrates [4], hydroxycarbonates
[12] and several more complex compounds [13–
20] and gels [21, 22]. Decomposition and heat treatment
are usually carried out in oxygen or air at temperatures
below 873 K, however the heat treatment can last from 1 h
to a few days. Preparations at temperatures B353 K have
also been reported [23, 24]. The type of treatment can
affect the structure and surfactants have been used to
control morphology of generate nanomaterials