Neutron and X-ray diffraction study of cubic [111] field cooled Pb(Mg1/3Nb2/3)O3

Abstract

Neutron and x-ray diffraction techniques have been used to study the competing long and short-range polar order in the relaxor ferroelectric Pb(Mg${}_{1/3}$Nb${}_{2/3}$)O${}_3$ (PMN) under a [111] applied electric field. Despite reports of a structural transition from a cubic phase to a rhombohedral phase for fields E $>$ 1.7 kV/cm, we find that the bulk unit cell remains cubic (within a sensitivity of 90${}^{\circ }$-$\alpha$ =0.03${}^{\circ }$)for fields up to 8 kV/cm. Furthermore, we observe a structural transition confined to the near surface volume or `skin' of the crystal where the cubic cell is transformed to a rhombohedral unit cell at T${}_c$=210 K for E $>$ 4 kV/cm, for which 90${}^{\circ }$-$\alpha$=0.08 $\pm$ 0.03${}^{\circ }$ below 50 K. While the bulk unit cell remains cubic, a suppression of the diffuse scattering and concomitant enhancement of the Bragg peak intensity is observed below T${}_c$=210 K, indicating a more ordered structure with increasing electric field yet an absence of a long-range ferroelectric ground state in the bulk. The electric field strength has little effect on the diffuse scattering above T${}_c$, however below T${}_c$ the diffuse scattering is reduced in intensity and adopts an asymmetric lineshape in reciprocal space. The absence of hysteresis in our neutron measurements (on the bulk) and the presence of two distinct temperature scales suggests that the ground state of PMN is not a frozen glassy phase as suggested by some theories but is better understood in terms of random fields introduced through the presence of structural disorder. Based on these results, we also suggest that PMN represents an extreme example of the two-length scale problem, and that the presence of a distinct skin maybe necessary for a relaxor ground state.

arXiv comment12 pages, 9 figures

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Cited by in corpus (22)

• The role of random electric fields in relaxors
• A reassessment of the Burns temperature and its relationship to the diffuse scattering, lattice dynamics, and thermal expansion in the relaxor PMN
• 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
• Competing orders in PZN-xPT and PMN-xPT relaxor ferroelectrics
• Random Electric Field Instabilities of Relaxor Ferroelectrics
• Paraelectric and Ferroelectric States in a Model for Relaxor Ferroelectrics
• Evidence for anisotropic polar nanoregions in relaxor PMN: A neutron study of the elastic constants and anomalous TA phonon damping
• A two-component model of the neutron diffuse scattering in the relaxor ferroelectric PZN-4.5%PT
• Infrared, terahertz, and microwave spectroscopy of the soft and central modes in Pb(Mg1/3Nb2/3)O3
• Condensation of the atomic relaxation vibrations in lead-magnesium-niobate at $T=T^{\ast }$
• Temperature independent diffuse scattering and elastic lattice deformations in relaxor PbMg1/3Nb2/3O3
• Spontaneous decay of a soft optical phonon in the relaxor ferroelectric PbMg${}_{1/3}$Nb${}_{2/3}$O${}_3$
• Coupled magnetic and ferroelectric excitations in PbFe_{1/2}Nb_{1/2}O_{3}
• Freezing of the local dynamics in the relaxor ferroelectric PZN-4.5PT
• Fluctuating defects in the incipient relaxor K${}_{1-x}$Li${}_x$TaO${}_3$ (x=0.02)
• Dipole-glass concept and history-dependent phenomena in relaxors
• Raman spectroscopic investigation of relaxor behavior in Pr doped SrTiO3 and Origin of Fano resonance
• Broadband critical dynamics in disordered lead-based perovskites
• Phonon coupling to dynamic short-range polar order in a relaxor ferroelectric near the morphotropic phase boundary
• Fast broadband cluster spin-glass dynamics in PbFe${}_{1/2}$Nb${}_{1/2}$O${}_3$
• Magnetic skin effect in Pb(Fe${}_{1/2}$Nb${}_{1/2}$)O${}_3$