Study of the preparation conditions for NiMn2O4 grown from hydroxide precursors

An investigation of mixed oxide route preparation routes for nickel manganite has confirmed that residual nickel oxide is present regardless of the particular conditions adopted [Wickham, D. G., Solid-phase equilibria in the system NiO–Mn2O3–O2. J. Inorg. Nucl. Chem., 1964, 26, 1369–1377; de Gyorgyfalva, G. D. C. C., Nolte, A. N. and Reaney, I. M., Correlation between microstructure and conductance in NTC thermistors produced from oxide powders. J. Eur. Ceram. Soc., 1999, 19, 857–860]. The co-precipitation of mixed hydroxides of nickel and manganese was successfully employed to eliminate any unreacted nickel oxide remaining after firing, though the requirements for single phase nickel manganite were investigated in detail and found to be quite stringent. Synthesized materials were characterized by X-ray powder diffraction measurements with diffraction patterns being analysed using the Rietveld technique. A systematic investigation into the optimum firing conditions confirmed that a minimal impurity content is achieved in samples rapidly heated to 800 °C, and fired for at least 48 h. Nickel oxide was found to be the dominant impurity phase at higher firing temperatures.