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
  • 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
  • To clarify the nature of this unusual observation, we show an extended constant-E scan taken at ∆E = 6 meV in Fig. 3 along with a constant-Q scan in the insert
  • Another important aspect which requires further study is exactly how the “waterfall” evolves, at much higher temperatures, into the standard optic mode dispersion as shown in Fig. 1 for PMN

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