ESR of Free Radicals in Ferroelectric and Antiferroelectric Arsenate Single Crystals

The electron spin resonance of gamma irradiated single crystals of KH₂AsO₄, KD₂AsO₄, NH₄H₂AsO₄, and ND₄D₂AsO₄ has been investigated. New paramagnetic centers present in several varieties and which exhibit a strong coupling with one ⁷⁵As atom have been described. At room temperature, their g tensor is nearly isotropic and their hyperfine couplings are axially symmetric. The annealing of these centers is examined and their behavior upon cooling down below T_c is described. All these centers which seem to belong to the same family have been identified as ${\mathrm{AsO}}_3^{\text{2−}}$ species. Their different varieties must be ascribed to different environments coming either from various proton environments or from several associations with varied impurities.