Electric dipole centres and colour centres in natural sodalite

Abstract

Experiments on an electric dipole centre, exhibiting multiple relaxation, in the natural mineral sodalite, are described. The concentration of the dipole centres is reduced upon X irradiation, whereas simultaneously colour centres and paramagnetic centres arise. Thermal bleaching restores the original concentrations. The interrelationships between these centres are established.

A model is proposed in which the dipole centre is ascribed to an interstitial monovalent metal ion (say a Na⁺ ion) acting as a charge compensator for an Al³⁺ ion, substituted for a Si⁴⁺ ion. This Al-Na complex may be destroyed by X rays, yielding an electron trapped at the sodium ion and a hole trapped at a nonbridging oxygen ion, adjacent to the Al³⁺ ion, to which both the optical and paramagnetic properties of the X ray induced centres are attributed.