Lattice dynamics and electromechanical response in disordered perovskites

Perovskite oxides with a charge/site disorder possess superior dielectric, ferroelectric and electromechanical properties. These functional properties are relevant for various technological applications, yet still there are many scientific challenges in the field. The phase diagrams of complex perovskites have an exotic crossover from relaxor to normal ferroelectric behaviour. The mechanism of the phase transitions in such phase diagrams are not well understood and remains one of the forefront problems in the field of ferroelectricity. In this work, several perovskite oxide systems with a charge disorder in the different site of the perovskite lattice are investigated. The lattice dynamics of these systems are thoroughly studied by broadband dielectric, IR and Raman spectroscopic studies. The studies revealed the evolution of (nano)domains and their contribution to the macroscopic properties. It revealed that the phase transitions and dielectric anomalies can be associated to the thermal evolution of the central (relaxation) mode. The electromechanical properties in macroscopic and microscopic scale is also reported. It was concluded that the complex local polar patterns contribute to the macroscopic reponse in a same manner although they are different at the nanoscale