研究目的

This paper aims to address the kinetic-growth limitation required to achieve a thermodynamically stable, ordered state in PMN, via synthesis of thin PMN heterostructure films with ordered layers of stoichiometric Pb[Mg2/3Nb1/3]O3 and PbNbO3 grown at lower temperature (<Torder–disorder = 1073 K).

研究成果

This work reports the first PMN thin film material with long-range cation order. Heterostructure films grown as alternate layers of Pb(Mg2/3Nb1/3)O3 and PbNbO3 are compared to PMN films grown from a single target. It was found that the (111) orientation facilitated the phase pure growth of 111 ordered heterostructure films, compared to the (001) orientation. The heterostructures showed significantly larger regions of chemical ordering. Selected area electron diffraction confirmed emergence of superlattice spots (1/2, 1/2, 1/2) with randomly distributed ordered domains as large as 100 nm. These heterostructures exhibited a dielectric constant of 800, loss tangents of approximately 0.03 and 2*remanent polarization of ≈11 μC cm?2 at room temperature. Polarization–electric field loops, Rayleigh data, and optical second harmonic generation measurements are consistent with the development of ferroelectric domains below 140 K. The comparative study with short-range ordered films elucidates the impact of long-range cation order in PMN on its electrical properties. Temperature-dependent permittivity measurements demonstrate reduced frequency dispersion compared to short-range ordered PMN films. It was observed that the relaxor behavior did not 'switch off' in the presence of longer range ordering along one axis, although the Rayleigh, polarization and thermal depolarization data are consistent with increased levels of longer-range ferroelectric ordering.

研究不足

The relaxor behavior did not turn 'off' completely in the ordered sample, despite observing increased size of chemically ordered regions in TEM. This suggests that the ordering observed is inadequate to drive a fully ferroelectric state.