Studies Of Field Induced Phase Transition In PLZT Antiferroelectric Single Crystalsnear Morphotropic Phase Boundary

(Pb,La)?Zr,Sn,Ti?O₃?PLZST?antiferroelectric single crystals with composition close to Morphotropic phase boundary?MPB?possess features of coexistence of tetragonal antiferroelectric?AFE?and rhombohedral ferroelectric?FE?phases in its microstructure.Due to the low Gibbs free energy difference between these two phases in MPB PLZST single crystals,the AFE-FE_in phase transition could be easily induced under external fields,such as electric field,temperature and stress,which will exhibit superior dielectric properties,electro-strains and pyroelectric properties,making it promising candidates in high sensitivity infrared detectors,large strain actuatorsand transducers design.C₁ composition PLZST antiferroelectric single crystal with a size of 5×5×5 mm³ wasgrown successfullyby using a modified flux method.A rhombohedral ferroelectric phase was induced once an electric field above antiferroelectric-ferroelectric phase transition field E_A-F was applied on a virgin [001]_c-cut crystal,accompanying with a large stain of 0.56%.Coexistence of tetragonal antiferroelectric phaseand rhombohedral ferroelectric phasewere observed by polarized light microscope?PLM?,which indicated that AFE and FE phase could be isolated or embedded into each other and form a transition region,namely,a “clamping polar effect” model.Soft mode theory was introduced to learn the field induced phase transition of PLZST with MPB compositions,in which the competition between long-range force?LRF?and short-range force?SRF?was considered to be themain reason for field induced phase transitions.Crystal with largelongitudinal strain was designed and grown by reducing E_A-F according to thetwo phases coexistence and “clamping polar effect” model.C₂ composition PLZST antiferroelectric single crystalwith a size of 5×5×5mm³wasgrown successfully.The [001]_c-cut crystal exhibited a dielectric peak at 120°C,accompanying with a large stain of 0.75%,resulting from the temperature induced AFE-FE_in phase transition and the reversible domain wall motion caused by phase transition.Meanwhile,an incommensurate modulation was also formed at the depolarization temperature?T_d?.The dielectric,ferroelectric,pyroelectric properties and the domain structures of PLZST single crystalswith different cuts were investigated systematically.A microscopic structure model for the broaden pyroelectric peak of[111]_c-cutPLZST single crystal was proposed to explain the stable mechanism of the induced ferroelectric phase.