0.67BiFeO_(3)-0.33BaTiO_(3)multiferroic ceramics doped with x mol%MnO_(2)(x=2-10)were synthesized by solid-state reaction.The formation of a perovskite phase with rhombohedral symmetry was confirmed by X-ray diffraction(XRD).The average grain sizes were reduced from 0.80mm to 0.50mm as increasing the Mn-doped levels.Single crystalline nature of the grains was revealed by high-resolution transmission electron microscopy(HRTEM)images and electron diffraction patterns.Polar nano-sized ferroelectric domains with an average size of 9 nm randomly distributed in the ceramic samples were revealed by TEM images.Ferroelectric domain lamellae(71°ferroelectric domains)with an average width of 5 nm were also observed.Vibrational modes were examined by Raman spectra,where only four Raman peaks at 272 cm^(-1)(E-4 mode),496 cm^(-1)(A_(1)-4 mode),639 cm^(-1),and 1338 cm^(-1)were observed.The blue shifts in the E-4 and A_(1)-4 Raman mode frequencies were interpreted by a spring oscillator model.The dieletric constants of the present ceramics as a function of the Mn-doped levels exhibited a V-typed curve.They were in the range of 350-700 measured at 10^(3)Hz,and the corresponding dielectric losses were in range of 0.43-0.96,approaching to 0.09 at 10^(6)Hz.
Perovskite ferroelectric nanostructures offer a wide range of functional properties(e.g.,dielectric switchability,piezoelectricity,pyroelectricity,high permittivities and strong electro-optic effects),which have received much attention in theelds of microelectronic devices miniaturization over the last few years.Pronounced size effects of the functional properties have been demonstrated in the perovskite ferroelectric nanostructures.Besides its intrinsic scientic value,fundamental understanding of the size effects in perovskite ferroelectric nanostructures has become critical item for developing a new generation of revolutionary nanodevices.In this article,a comprehensive review of the state-of-the-art research progress on the size effects in perovskite ferroelectric nanostructures which have been achieved from both experiment and theory is provided.It begins with a historical perspective of the size effects in perovskite ferroelectrics,and then highlight the recent progress on the theoretical studies of the size effects in perovskite ferroelectric nanostructures which have been achieved by using different numerical approaches(e.g.,phenomenological approaches,rst-principle computations and the Ising model in a transverseeld).The current progress of the experimental testing of the size effects in perovskite ferroelectric nanostructures(e.g.,nanoparticles,nanowires,nanotubes and nanolms)is summarized.Finally,the perspectives toward the future challenges of the size effects in perovskite ferroelectric nanostructures is reviewed.
