Soft Phonon Anomalies in the Relaxor FerroelectricPb(Zn1/3Nb2/3)0.92Ti0.08O3

Motivated by these experimental and theoretical results, we have studied the dynamics of the soft polar optic phonon mode in a high quality single crystal of PZN-8%PT, for which the measured value of d33 is a maximum, using neutron inelastic scattering methods

P. M. Gehring; S.-E. Park; G. Shirane

2002

Scholarcy highlights

  • Neutron inelastic scattering measurements of the polar transverse optic phonon mode dispersion in the cubic relaxor Pb(Zn1/3Nb2/3)0.92Ti0.08O3 at 500 K reveal anomalous behavior in which the optic branch appears to drop precipitously into the acoustic branch at a finite value of the momentum transfer q = 0.2 ̊A−1 measured from the zone center
  • Because the parent compounds Pb(Zn1/3Nb2/3)O3 and PbTiO3 form a solid solution, it was possible to tune the stoichiometry of the material to lie near the morphotropic phase boundary that separates the rhombohedral and tetragonal regions of the phase diagram
  • The dielectric and piezoelectric properties of single crystals of both PZN-xPT and PMN-xPT have since been examined by Park et al who measured the strain as a function of applied electric field. These materials were found to exhibit remarkably large piezoelectric coefficients d33 > 2500 pC/N and strain levels S ∼ 1.7% for rhombohedral crystals oriented along the pseudo-cubic direction
  • This level of strain represents an order of magnitude increase over that presently achievable by conventional piezoelectric and electrostrictive ceramics including PZT. That these ultrahigh strain levels can be achieved with nearly no dielectric loss due to hysteresis suggests both PMNxPT and PZN-xPT hold promise in establishing the generation of solid state transducers
  • A very recent theoretical advance in our understanding of these materials occurred when it was shown using first principles calculations that the intrinsic piezoelectric coefficient e33 of MPB PMN-40%PT was dramatically enhanced relative to that for PZT by a factor of 2.7. Motivated by these experimental and theoretical results, we have studied the dynamics of the soft polar optic phonon mode in a high quality single crystal of PZN-8%PT, for which the measured value of d33 is a maximum, using neutron inelastic scattering methods
  • We find striking anomalies in the TO phonon branch that we speculate are directly caused by these PMR
  • Tentative evidence for this has already been observed at room temperature in neutron scattering measurements on PMN

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