Charge Transfer Model of Polar Clusters, Nature of Their Infinite-Range Interaction and Freezing Phenomena in PMN-Type Relaxors

A charge transfer model of polar clusters (PC) in PMN-like relaxors is developed. Charge transfer regions consist of correlated charge transfer vibronic states which are responsible for PC formation on the interfaces of ordered chemical fluctuation regions (CFR) in the framework of the model. Dipole-dipole cross-relaxation between charge transfer vibronic states in PCs makes here the contribution to relaxor-type losses. The co-operative phenomena and phase transitions in such PC system for low PC concentration case can be explained due to infinite-range PC-PC interaction via elastic field. The latter field interacts with PC polarization fluctuations due to local piezo-electric effect induced by quasi-static PC polarization. This mechanism acts in parallel way with the second one for electric dipole-dipole infinite-range PC-PC interaction via TO phonons. The model can explain freezing phenomena appearing at T < T f ( T f is a freezing temperature) due to co-operative memory effects in the long-range correlated glass-like state.

Keywords:

• Relaxors
• Polar Clusters
• Charge Transfer
• Local Instability
• Long Range Interaction
• Freezing Phenomena