  Piezoelectric PZT solid solutions were studied as a function of pressure and
temperature. Moderate pressure is found to induce phase transitions to
monoclinic phases (Cm,Cc) for Ti-rich PZT, which are the same ferroelectric
phases responsible for the high piezoelectric properties of the MPB. The
following transformation sequence P4mm -> Cm -> Cc -> F1 -> F-1 was identified
upon increasing pressure. Compression behaviour is dominated by: (1) a rotation
and a reduction of the spontaneouspolarization and (2) octahedral tilting
leading to unit cell doubling. Future studies as a function of pressure,
temperature and electric field on single crystals of heterovalent relaxor
ferroelectric isotypes of PZT are proposed in order to better understand these
potentially technologically-important piezoferroelectric materials.
