Centers of Tl-related paramagnetic Tl2+ (6s1) and Tl0 (6p1) type were produced by low-temperature X-ray irradiation of ferroelectric Tl-doped single crystals. Extensive electron paramagnetic resonance investigations were used to determine their intrinsic properties, and sensitivities as paramagnetic probes. When compared to s-type Tl2+ centers, it was found that the p-type Tl0 centers were much more sensitive to small variations, in the local crystal field, that were associated with these transformations. The electron paramagnetic resonance spectra provided information on unit-cell tripling in the P21cn phase, as well as symmetry-lowering and lattice dynamics in the C1c1 phase. Temperature-induced continuous changes in the electron paramagnetic resonance spectra of both Tl0 and Tl2+ centers were attributed to the effect of the soft modes that were responsible for the 74K structural phase transition.

EPR Probing of Low Temperature Structural Phases of Rb2ZnCl4 Crystals with Tl0 and Tl2+ Centers. M.Stefan, S.V.Nistor, E.Goovaerts, D.Schoemaker: Physical Review B, 2004, 69[10], 104107 (11pp)