Abstract
Abstract Studies of the sintering behaviour of NiMn2O4 semiconducting ceramics at 1100°C under oxygen atmosphere show the advantage of a powder prepared by thermal decomposition of oxalate mixed crystals NiMn2 (C2O4)3. 6H2O at 450°C for the formation of dense ceramics with homogeneous microstructure. The microstructure of the semiconductor ceramics was established by image analysis. SEM and EDX indicate a phase separation related to partial oxygen loss as observed by thermogravimetry and redox analytic measurements. Reoxidation to a single-phase homogeneous microstructure by annealing at 800°C is possible only in porous samples. NiMn2O4 is not stable in oxygen at 1100°C. The spinel decomposes into NiO and a Mn-rich spinel matrix NixIIMn1−xIIMn2IIIO4. For producing a reproducible semiconducting ceramics it is necessary to stimulate sintering by separation of NiO. A one-phase spinel is obtained by reoxidation of long duration.
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