Field-induced strains and polarization switching mechanisms in La-modified lead zirconate titanate ceramics

The field-induced strain characteristics have been investigated for a sequence of La-modified lead zirconate titanate (PLZT) compositions. It was shown that the increase in the ease of polarization switching is essential for maximum electrically induced strains in PLZT ceramics. For PLZT compositions close to the morphotropic phase boundary this was realized by adjusting the base composition to be close to the boundary between tetragonal and rhombohedral states, where the polarization has a maximum number of equivalent orientations (6 for tetragonal plus 8 for rhombohedral) by which to switch. For PLZT compositions located in either the rhombohedral or tetragonal states, the ease of polarization switching was facilitated by La doping until the point where the normal micron-sized ferroelectric domains began to break up into tweedlike subdomain structures. Polarization switching may then occur through the subdomain state, rather than by the creation and subsequent motion of normal micron-sized domain boundaries. (C) 1996 American Institute of Physics.