Mn2+defects in LiNbO3: an electron nuclear double resonance (ENDOR) investigation of the Mn2+site and the local disorder

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Abstract
With ENDOR, Mn2+ centres in both stoichiometric and congruent LiNbO3 have been investigated. An analysis of four identified Li shells with 24 Li neighbours gives sufficient proof for the Mn2+ occupying a Li site. In stoichiometric LiNbO3 both neighbouring on-axis Nb nuclei were also identified and found to experience changed electric field gradients compared with remote Nb nuclei and NMR data in the literature. Signs of the parameters of the Mn2+ spin Hamiltonian (A/sub //, perpendicular to /O, P>0) have been determined. Most centres probably contain a defect such as charge-compensating Li vacancy in the first Li shell. As inferred from line-broadening effects, additional defects, especially in congruent crystals, have a measurable influence on the relaxation of nuclei near to the Mn2+.