Abstract
EPR and dielectric properties of lead germanate Pb5Ge3 O11 (PGO) crystals doped with Cu2+ are reported. EPR spectra testify that Cu2+ substitute for Pb2+ in the sites of trigonal point symmetry and equi-probably occupy one of three off-center positions shifted from lattice point in the plane perpendicular to polar axis c. Motional averaging of low symmetry EPR spectra just as low frequency dielectric dispersion indicate thermally activated hopping of Cu2+ ions between off-center positions. Own frequency (τ0) −1 ∼1012Hz and activation energy W = 0.24 eV of Cu2+ local dynamics have been determined from EPR and dielectric measurements. Properties of PGO:Cu2+ near ferroelectric phase transition are discussed on the basis of semi-phenomenological approach. It has been shown that PGO properties are influenced through static distortions accompanying Cu2+ off-center location in the structure. Local dynamics of Cu2+ ions between off-center positions do not effect on dynamic properties of a crystalline matrix near TC.
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