Charge Transfer Vibronic Excitons, Bi-Polarons, and Iron Group Impurities in Ferroelectric Oxides: Pb x Nb y O z —Ceramics (original) (raw)

Ferroelectrics, 2004

Abstract

ABSTRACT The simulation of chemical fluctuation regions in the PMN-like relaxors by growth of the PbxNbyOz—ceramics was performed. The coexistence of PbxNbyOz—clusters with different chemical composition inclusive Nb as well as Nb ions was assumed. An existence of paramagnetic Cr ions on Nb sites with charge compensation by two-oxygen hole bi-polarons with intermediate radius and in singlet states was suggested on the basis of EPR-experiment. A dissociation of such a bi-polaron with temperature via crossover with large radius bi-polaron produces finally the EPR-active free holes. They take part in spectrum motional averaging due to hopping transitions between different PbxNbyOz—clusters. New light induced EPR-lines were detected. This new lines are connected with two origins. First, it is effect of light-induced complexes which are appeared due to trapping of a space charge on the core-like Fe ions located on Nb sites in PbxNb yOz—clusters. Second, it is effect of Ti ions on Pb sites which are appeared under successive photo-recharging of non-paramagnetic Ti Pb2+ and paramagnetic Ti Pb2+ ions in accord with photo-chemical recharging transformation: Ti Pb2+ ↞ Ti Pb2+ ↞ Ti Pb2+. Charge transfer vibronic excitons with O → Nb charge transfer was directly detected by photoluminescence studies. R-line Cr impurity photoluminescence manifestation independently confirms the Cr ion appearance on Nb ion sites in such matrices.

Hike Asatryan hasn't uploaded this paper.

Let Hike know you want this paper to be uploaded.

Ask for this paper to be uploaded.