Electron paramagnetic resonance study of the proton-assisted thermal decompositions of MnO₄^-and CrO₄^2- doped into (NH₄)₂SO₄ and LiNH₄SO₄ crystals

This paper reports a novel application of electron paramagnetic resonance (EPR) to the detection of the thermal decompositions of MnO₄^-4and the CrO₄^2- doped into (NH₄)₂SO₄ and LiNH₄SO₄ crystals. By heating the sample crystals to temperatures well below the dissociation temperature or the high-temperature structural phase transition temperatures, isolated Mn²⁺and Cr³⁺ are detected by EPR. By a comparative study, one can conclude that the thermal decomposition of MnO₄^- into Mn²⁺ or of CrO₄^2-into Cr³⁺, 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.