Synthesis and characterization of mixed manganese-gallium oxides Mn3-xGaxO4 (x=1-2) with the spinel structure

Manganese-gallium oxide samples with the cationic ratio Mn: Ga = 2: 1, 1.7: 1.3, 1.5: 1.5, 1.3: 1.7 and 1: 2 were synthesized via coprecipitation followed by calcination in argon over a wide temperature range, 600-1200 degrees C. Physicochemical characteristics of the samples were examined by means of XRD, BET, TG with mass spectroscopy, and IR spectroscopy. The XRD, IR spectroscopy showed that the Mn3-xGaxO4 mixed oxides with the spinel structure are formed in the entire temperature range, 600-1200 degrees C. Samples with a cation ratio Mn: Ga = 1.7: 1.3, 1.5: 1.5 at 1000-1200 degrees C. and Mn: Ga = 1.3: 1.7 at 1200 degrees C. are single-phase ones according to XRD. The cation distribution over tetrahedral and octahedral spinel positions was obtained by the Rietveld method. The spinel phases synthesized at 600 degrees C (low-temperature samples) are nanocrystalline and have CSR sizes of 10-15 nm. Ex situ and in situ XRD, TG with mass spectroscopy studies revealed that low-and high-temperature Mn3-xGaxO4 oxides substantially differ from each other. Strongly differing unit cell parameters of the spinel phase in low-(600-800 degrees C) and high-temperature (1000-1200 degrees C) samples were revealed. The presence of excess oxygen in low-temperature Mn3-xGaxO4 phases was supposed. In situ XRD in flowing helium and TG with mass spectroscopy demonstrated a two-step loss of oxygen. (C) 2017 Elsevier B.V. All rights reserved.