EPR of the thermally produced CrO^3- ₄ in CrO^2- ₄-doped (NH₄)₃H(SeO₄)₂ crystals

Two spin 1 2 paramagnetic species (species I and species II) are detected by electron paramagnetic resonance (EPR) in CrO^2- ₄-doped (NH₄)₃H(SeO₄)₂ single crystals, after the host crystals had been heated to temperatures well below their decomposition temperature. When heat treated at lower temperatures ({reversed tilde equals}90°C), only one species (species I) was detected by EPR. The EPR spectrum of this species was identical to that of the CrO^3- ₄ species produced by γ-irradiation of the sample crystals. By comparing the thermal treatment behaviors of the CrO^2- ₄-doped Rb₃H(SeO₄)₂ and Cs₃H(SeO₄)₂ crystals, it was established that the electronic defect acquired by the CrO^2- ₄ to form the thermally produced CrO^3- ₄ (I) originates from the NH⁺ ₄ group. It is difficult to determine with certainty from the g-values alone the identity of species II. This species could be a CrO^- ₃ or a Cr⁵⁺ ion.