POLARIZATION SWITCHING MECHANISMS AND ELECTROMECHANICAL PROPERTIES OFLA-MODIFIED LEAD-ZIRCONATE-TITANATE CERAMICS

The electromechanical properties of (Pb1-xLax) (ZryTi1-y)O-3 [PLZT x/y /(1 - y)] have been investigated in the compositional range O < x < 0. 10 for y = 0.65 (rhombohedral PLZT) and O < x < 0.18 for y = 0.40 (tet ragonal PLZT). Both field-induced strains (epsilon-E) associated with polarization switching and piezoelectric responses (d(33)) were studie d. Transmission electron microscopy (TEM) and dielectric investigation s were also performed. Room temperature TEM investigations revealed co mmon trends in the domain structure with increasing La content for bot h PLZT x/65/35 and x/40/60, including a micron-sized domain structure, a subdomain tweed-like structure, and a nanopolar domain state. Chang es in the field-induced strains and piezoelectric properties were then related to these microstructural trends. The dominant electromechanic al coupling mechanism in the micron-sized domain state was found to be piezoelectricity. However, an electrostrictive coupling became appare nt with the appearance of the subdomain tweed-like structures, and bec ame stronger in the nanopolar domain state. It is believed that polari zation switching can occur through 70 degrees or 110 degrees domains, the subdomain tweed-like structure, or nanopolar domains depending on La content.