Dynamic origin of the morphotropic phase boundary - Soft modes and phase instability in 0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3

Abstract

We report neutron inelastic scattering on single crystal 0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3 (PMN-0.32PT), a relaxor ferroelectric material that lies within the compositional range of the morphotropic phase boundary (MPB). Data were obtained between 100 K and 600 K under zero and non-zero electric field applied along the cubic [001] direction. The lowest energy, zone-center, transverse optic phonon is strongly damped and softens slowly at high temperature; however the square of the soft mode energy begins to increase linearly with temperature as in a conventional ferroelectric, which we term the soft mode "recovery," upon cooling into the tetragonal phase at TC. Our data show that the soft mode in PMN-0.32PT behaves almost identically to that in pure PMN, exhibiting the same temperature dependence and recovery temperature even though PMN exhibits no well-defined structural transition (no TC). The temperature dependence of the soft mode in PMN-0.32PT is also similar to that in PMN-0.60PT; however in PMN-0.60PT the recovery temperature equals TC. These results suggest that the temperature dependence and the energy scale of the soft mode dynamics in PMN-xPT are independent of concentration on the Ti-poor side of the MPB, but scale with TC for Ti-rich compositions. Thus the MPB may be defined in lattice dynamical terms as the concentration where TC first matches the recovery temperature of the soft mode. High-resolution x-ray studies show that the cubic-to-ferroelectric phase boundary shifts to higher temperatures by an abnormal amount within the MPB region in the presence of an electric field. This suggests that an unusual instability exists within the apparently cubic phase at the MPB.

13 pages, 6 figures

References in corpus (27)

• A monoclinic ferroelectric phase in the Pb(Zr1-xTix)O3 solid solution
• A tetragonal-to-monoclinic phase transition in a ferroelectric perovskite: the structure of PbZr(0.52)Ti(0.48)O3
• Phase diagram of the ferroelectric-relaxor (1-x)PbMg(1/3)Nb(2/3)O3-xPbTiO3
• Polarization rotation via a monoclinic phase in the piezoelectric 92%PbZn1/3Nb2/3O3-8%PbTiO3
• Stability of the monoclinic phase in the ferroelectric perovskite PbZr(1-x)TixO3
• Monoclinic phase in the relaxor-based piezo-/ ferroelectric Pb(Mg${}_{1/3}$Nb${}_{2/3})O_3$-PbTiO${}_3$ system
• Phase diagram of the relaxor ferroelectric (1-x)PbZn(1/3)Nb(2/3)O3-xPbTiO3
• Monoclinic structure of unpoled morphotropic high piezoelectric (PbMg1/3Nb2/3O3)0.65-(PbTiO3)0.35 and (PbZn1/3Nb2/3O3)0.91-(PbTiO3)0.09 compounds
• X-ray and Neutron Diffraction Investigations of the Structural Phase Transformation Sequence under Electric Field in 0.7Pb(Mg1/3Nb2/3)-0.3PbTiO3 Crystals
• Electric-field induced phase transitions in rhombohedral PZN-xPT
• Soft Mode Dynamics Above and Below the Burns Temperature in the Relaxor Pb(Mg_1/3Nb_2/3)O_3
• Ferroelectric Ordering in the Relaxor Pb(Mg1/3Nb2/3)O3 as Evidenced by Low-Temperature Phonon Anomalies
• Soft Phonon Anomalies in the Relaxor Ferroelectric Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3
• Neutron Diffraction Study of Field Cooling Effects on Relaxor Ferroelectrics Pb[(Zn_{1/3} Nb_{2/3})_{0.92} Ti_{0.08}] O_{3}
• Intermediate ferroelectric orthorhombic and monoclinic MB phases in [110]- electric field cooled Pb(Mg1/3Nb2/3)O3-30%PbTiO3 crystals
• Universal Static and Dynamic Properties of the Structural Transition in Pb(Zn1/3Nb2/3)O3
• Ground State of Relaxor Ferroelectric $Pb(Z{n}_{1/3}N{b}_{2/3})O_3$
• Mode-coupling and polar nanoregions in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3
• Dynamical effects of the nanometer-sized polarized domains in Pb(Zn1/3Nb2/3)O3
• A Universal Phase Diagram for PMN-xPT and PZN-xPT
• Damped Soft Phonons and Diffuse Scattering in 40PMN-60PT
• Anomalous transverse acoustic phonon broadening in the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O_3
• An Anomalous Phase in the Relaxor Ferroelectric Pb(Zn${}_{1/3}$Nb${}_{2/3}$)O${}_3$
• Strong Influence of the diffuse component on the lattice dynamics in Pb(Mg${}_{1/3}$Nb${}_{2/3}$)O${}_3$
• Direct observation of the near-surface layer in Pb(Mg${}_{1/3}$Nb${}_{2/3}$)O${}_3$ using neutron diffraction
• Structural phase transformation and phase boundary/stability studies of field-cooled Pb(Mg1/3Nb2/3O3)-32%PbTiO3 crystals
• The Structural Phase Transition of the Relaxor Ferroelectric 68%PbMg1/3Nb2/3O3-32%PbTiO3

Cited by in corpus (10)

• Interplay between static and dynamic polar correlations in relaxor Pb(Mg_{1/3}Nb_{2/3})O_{3}
• Soft phonon columns on the edge of the Brillouin zone in the relaxor PbMg1/3Nb2/3O3
• Grain Size Influence on Dynamics of Polar Nanoclusters in PMN-35%PT Ceramics: Broadband Dielectric and Infrared Spectra
• Competing orders in PZN-xPT and PMN-xPT relaxor ferroelectrics
• Evidence for anisotropic polar nanoregions in relaxor PMN: A neutron study of the elastic constants and anomalous TA phonon damping
• Coupled magnetic and ferroelectric excitations in PbFe_{1/2}Nb_{1/2}O_{3}
• Spontaneous decay of a soft optical phonon in the relaxor ferroelectric PbMg${}_{1/3}$Nb${}_{2/3}$O${}_3$
• Broadband critical dynamics in disordered lead-based perovskites
• Fast broadband cluster spin-glass dynamics in PbFe${}_{1/2}$Nb${}_{1/2}$O${}_3$
• Soft Phonon Modes and Diffuse Scattering in Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 Relaxor Ferroelectrics