Proton-Thallium Coupling in Thallium Doped Crystals of the KDP family

A previous model for proton-thallium coupling in thallium doped crystals of the KDP family, is corrected and extended in order to explain new ESR experiments in the temperature range 20–120 K. According to the reviewed model, two kind of centers, a symmetry-preserving and a symmetry-breaking, appear in those crystals and coexist in a temperature range. At low temperatures only the symmetry-breaking center is observed, whereas above about 77 K one can observe only the symmetry-preserving center. A semi-quantitative analysis of the exprimental results is presented, based on the new model.