An EPR study of primary paramagnetic centres in Cd2+-doped vaterite

Abstract

In order to find out how cadmium ions influence the formation and stability of paramagnetic centres in the vaterite phase, primary paramagnetic centres formed by γ-irradiation at 77 K were studied. Cd^2+•CO₃³⁻, ^•Cd^+• CO₃⁻ and ^•H atoms were detected at 77 K, and their transformation to the secondary species, ^•Cd⁺←O⁻ and ^•CO₂⁻, was followed as a function of temperature. Cd doped into vaterite caused broadening of the EPR lines due to the ^•CO₃⁻ hole of orthorhombic symmetry, suggesting that Cd ions are located only in the calcite structure. Thus, Cd ions may be considered as nuclei for calcite formation in the vaterite phase. The mechanism of Cd-induced calcite formation in the vaterite-precipitating system is suggested.