Macroscopic heterophase pattern in Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals


Polarization dependence of the Raman scattering intensities demonstrate that lamellar structures observed in (1x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals are composed of tetragonal-like and rhombohedral-like layers extending over macroscopic (mm) lengths. Lamellar heterostructures, observed in PMN-0.32PT single crystals are formed in samples cooled under bias electric field applied along [001]pc and then zero-field heated to the vicinity of the so-called depoling temperature TRT. Similar structures were also encountered at ambient conditions. Spatially resolved polarized Raman scattering techniques confirmed that the stripe pattern is due to the coexistence of the phases attached to the opposite sides of the morphotropic phase boundary in the temperature-composition phase diagram.

Raman spectra
a) Optical micrograph in a reflection mode, and (b) schematic illustration. Red crosses indicate orientation of polarizers on incident and scattered beam in configurations with a minimum Raman intensity at 570 cm−1. Right panel shows angular dependence of the I570/I510 intensity ratio for the parallel-polarized Raman scattering intensities, evaluated from the measurements taken at ambient conditions. Panels allow us to compare (c) data taken in the dark stripe, (d) data taken in a single-domain ([111]pc-poled) sample, (e) data taken in a multidomain, frustratively poled ([100]pc-poled) sample, and (f) data taken in the light stripe. The scattering geometry with respect to the pseudocubic crystallographic axes is common to all four cases displayed.