Coexistence and competition of local- and long-range polar orders in a ferroelectric relaxor

We have performed a series of neutron diffuse scattering measurements on a single crystal of the solid solution $\mathrm{Pb}\left({\mathrm{Zn}}_{1∕3}{\mathrm{Nb}}_{2∕3}\right){\mathrm{O}}_3$ doped with 8% $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_3$, a relaxor compound with a Curie temperature $T_C\sim 450\mathrm{K}$, in an effort to study changes in local polar orders associated with the polar nanoregions (PNR) when the material enters the ferroelectric phase. The diffuse scattering intensity increases monotonically upon cooling in zero field, but the rate of increase varies dramatically around different Bragg peaks. These results can be explained by assuming that corresponding changes occur in the ratio of the optic and acoustic components of the atomic displacements within the PNR. Cooling in the presence of a modest electric field $\vec{E}$ oriented along the [111] direction alters the shape of diffuse scattering in reciprocal space, but does not eliminate the scattering as would be expected in the case of a classic ferroelectric material. This suggests that a field-induced redistribution of the PNR has taken place.

Figure 1

(Color online) A schematic of the diffuse scattering intensity distribution in PZN-8%PT measured in the $\left(HKK\right)$ scattering plane around the (200), (300), (111), $\left(\overline{1}11\right)$, and (022) Bragg peaks at $300\mathrm{K}$ after (a) zero-field cooling and (b) field cooling with $E=2\mathrm{kV}∕\mathrm{cm}$ along [111]. The arrows indicate the linear scans performed in our measurements.

Figure 2

(Color online) Diffuse intensity linear profiles, measured along the [011] direction around the (300), (200), (111), and $\left(\overline{1}11\right)$ peaks, are shown from top to bottom, respectively. The lines through the data are fits to Gaussian functions of the reduced wave vector $q$ and are merely guides to the eye. The weak peaks in the (111) and $\left(\overline{1}11\right)$ scans near $K\sim 0.17$ are from aluminum powder lines. The heights of the error bars correspond to twice the square root of the number of neutron counts.

Figure 3

(Color online) Integrated diffuse scattering intensity vs temperature measured near the (a) (220), (b) (200), (c) (300), and (d) (111) Bragg peaks. The (red) open circles represent ZFC data while the (blue) solid circles are FC data for $E=2\mathrm{kV}∕\mathrm{cm}$ oriented along the [111] direction.

Figure 4

(Color online) A schematic showing the PNR configurations in a relaxor system in (a) the paraelectric phase, (b) ZFC into the ferroelectric phase, and (c) FC into the ferroelectric phase. The large arrows indicate the polarization of the ferroelectric domains separated by domain walls (solid lines). The small squares represent the PNR.