Relaxor Behavior In Ordered Lead Magnesium Niobate (Pbmg1/3nb2/3o3) Thin Films

The local compositional heterogeneity associated with the short-range ordering of Mg and Nb in PbMg1/3Nb2/3O3 (PMN) is correlated with its characteristic relaxor ferroelectric behavior. Fully ordered PMN is not prepared as a bulk material. This work examines the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg2/3Nb1/3)O-3 and PbNbO3, as suggested by the random-site model. 100 nm thick, phase-pure films are grown epitaxially on (111) SrTiO3 substrates using alternate target timed pulsed-laser deposition of Pb(Mg2/3Nb1/3)O-3 and PbNbO3 targets with 20% excess Pb. Selected area electron diffraction confirms the emergence of (1/2, 1/2, 1/2) superlattice spots with randomly distributed ordered domains as large as approximate to 150 nm. These heterostructures exhibit a dielectric constant of 800, loss tangents of approximate to 0.03 and 2x remanent polarization of approximate to 11 mu C cm(-2) at room temperature. Polarization-electric field hysteresis loops, Rayleigh data, and optical second-harmonic generation measurements are consistent with the development of ferroelectric domains below 140 K. Temperature-dependent permittivity measurements demonstrate reduced frequency dispersion compared to short range ordered PMN films. This work suggests a continuum between normal and relaxor ferroelectric behavior in the engineered PMN thin films.