Electron Spin Resonance of Radiation Damage Centers in NH4H2PO4 Single Crystal Doped with K2SeO4

Abstract

Radiation damage centers in ADP(NH 4 H 2 PO 4 ):K 2 SeO 4 mixed crystal were studied with ESR in the temperature range from 90 K to 350 K. It is found that there are SeO 4 3- , SeO 4 - and SeO 3 - radicals in the crystal, and that SeO 4 tetrahedral unit takes substitutionally the position of PO 4 unit. The ESR spectrum of SeO 4 3- radical has well-resolved proton super-hyperfine structure which shows the “quintet to triplet” transition, and exhibits domain splitting in low temperature range as seen on AsO 4 4- radical in KDA(KH 2 AsO 4 ). Using the temperature dependence of the domain splitting and line widths, the correlation time for the motion of Se 77 nucleus was estimated. The temperature dependence of correlation times is well fitted to the Arrhenius law: τ c =τ c o ·exp ( E a / k T ) with E a =0.19 eV for ADP:K 2 SeO 4 and E a =0.11 eV for KDP:K 2 SeO 4 .