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[en] The effect of mechanical stress on the direct piezoelectric properties of pre-poled (1 − x)(Na0.5Bi0.5)TiO3–xBaTiO3 (NBT–xBT) in the range 4% ≤ x ≤ 13% was studied in situ using a mechanical load frame. Prior to mechanical loading, compositions near the morphotropic phase boundary (MPB, x = 6–7% BT) exhibited enhanced ferroelectric and piezoelectric properties compared to compositions further from the MPB. Specifically, the lowest ferroelectric coercive field and highest piezoelectric coefficient within this composition range occur at x = 7% BT. During mechanical compression, the MPB compositions exhibited the lowest depoling stress. The results demonstrate that, while favorable piezoelectric and ferroelectric properties can be obtained at compositions near the MPB, these compositions are also the most susceptible to the effects of mechanical depoling. Ferroelastic domain wall motion is suggested as the primary factor that may be responsible for these behaviors.
[en] In this paper, the effective pyroelectric coefficient and polarization offset of the compositionally step-like graded multilayer ferroelectric structures have been studied by use of the first-principles approach. It is exhibited that the dielectric gradient has a nontrivial influence on the effective pyroelectric coefficient, but has a little influence on the polarization offset; and the polarization gradient plays an important role in the abnormal hysteresis loop phenomenon of the compositionally step-like graded ferroelectric structures. Moreover, the origin of the polarization offset is explored, which can be attributed to the polarization gradient in the compositionally step-like graded structure.
[en] We demonstrate that the morphotropic phase boundary of the lead-free ferroelectric system xBiNi0.5Zr0.5O3-(1-x)PbTiO3 (NBT-xBT) can be uniquely distinguished by a reduced polarizationstate along with a non-uniform attening of the local potential function of A- and B-site cationsof the perovskite-type structure. This establishes a robust structure-property connections based onthe atomic-level structural correlations which elucidates the long-standing question: why the MPBof NBT-xBT does not excel as much as Pb-based materials do; and further help to develop strategyin designing ecient lead-free ferroelectric systems.
[en] Influence of ZnO additive on structure, microstructure, dielectric, ferroelectric and local piezoelectric properties of (K0.5Na0.5)NbO3 – based ceramics have been studied. Increase in dielectric parameters and effective d33 piezoelectric coefficients was observed.
[en] We consider phase transitions in 2D XY-like systems with long-range dipole-dipole interactions and demonstrate that BKT-type phase transition always occurs separating the ordered (ferroelectric) and the disordered (paraelectric) phases. The low-temperature phase corresponds to a thermal state with bound vortex-antivortex pairs characterized by linear attraction at large distances. Using the Maier-Schwabl topological charge model, we show that bound vortex pairs polarize and screen the vortex-antivortex interaction, leaving only the logarithmic attraction at sufficiently large separations between the vortices. At higher temperatures the pairs dissociate and the phase transition similar to BKT occurs, though at a larger temperature than in a system without the dipole-dipole interaction.
[en] The interfaces of polar oxide heterostructures can display electronic properties unique from the oxides they border, as they require screening from either internal or external sources of charge. The screening mechanism depends on a variety of factors, including the band structure at the interface, the presence of point defects or adsorbates, whether or not the oxide is ferroelectric, and whether or not an external field is applied. In this review, we discuss both theoretical and experimental aspects of different screening mechanisms, giving special emphasis to ways in which the mechanism can be altered to provide novel or tunable functionalities. We begin with a theoretical introduction to the problem and highlight recent progress in understanding the impact of point defects on polar interfaces. Different case studies are then discussed, for both the high thickness regime, where interfaces must be screened and each interface can be considered separately, and the low thickness regime, where the degree and nature of screening can be manipulated and the interfaces are close enough to interact. We end with a brief outlook toward new developments in this rapidly progressing field. (review)