Thermally reversible transformation between free radicals in the paraelectric phase of irradiated KH2AsO4crystals

New EPR investigations in the paraelectric phase of $\gamma$-irradiated K${\mathrm{H}}_2$As${\mathrm{O}}_4$ crystals show the existence of a thermally reversible transformation between ${\mathrm{As}{\mathrm{O}}_4}^{4-}$ and ${\mathrm{As}{\mathrm{O}}_3}^{2-}$ free radicals. The transformation obeys a linear law, the parameters of which depend on the history of the crystal. We postulate that the phenomenon is allowed by interbond proton jumps between O-H ··· O bonds and that the ${\mathrm{As}{\mathrm{O}}_3}^{2-}$ radical is the consequence of the pairing of the ${\mathrm{As}{\mathrm{O}}_4}^{4-}$ radical with the $D$ defect which is assumed in theories of the proton-conductivity mechanisms.