Defect models of the low and high temperature centres of Cr3+ in α-LiIO3:Cr3+ crystals

By analysing the EPR spectra of α-LiIO3:Cr3+, the defect models of a low temperature centre Cr3+L and two high temperature centres Cr3+H1and Cr3+H2 are suggested. In centre Cr3+L, the Cr3+ ion replaces the Li+ ion and excess charge is compensated by two nearest Li+ vacancies on the same axis. In centres Cr3+H1and Cr3+H2, the Li+ vacancies below and above the Cr3+ ion are, respectively, dissociated from the low temperature centre Cr3+L. The suggestions are supported by the theoretical calculations of EPR parameters D, g parallel and g perpendicular for the three Cr3+ centres. The reasonableness of these models is discussed. (author)