Electron paramagnetic resonance study of the proton-assisted thermal decompositions of MnO 4−and CrO 42− doped into (NH 4) 2SO 4 and LiNH 4SO 4 crystals

Abstract

This paper reports a novel application of electron paramagnetic resonance (EPR) to the detection of the thermal decompositions of MnO 4 −4and the CrO 4 2− doped into (NH 4) 2SO 4 and LiNH 4SO 4 crystals. By heating the sample crystals to temperatures well below the dissociation temperature or the high-temperature structural phase transition temperatures, isolated Mn 2+and Cr 3+ are detected by EPR. By a comparative study, one can conclude that the thermal decomposition of MnO 4 − into Mn 2+ or of CrO 4 2−into Cr 3+, is accomplished through a solid-state chemical reaction between the thermally-excited ammonium hydrogens and the permanganate or the chromate oxygens. It can be inferred that the ammonium hydrogens participating in the thermal decomposition process are mainly the “free” protons released by the ammonium groups.