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As a representative boundary, interphase-interface may affect the strength or ductility of multilayered composites dramatically. However, the effect of the interface with mismatch dislocations on the mechanical behavior of multilayered composites is still not clear. In the present work, we performed molecular dynamics simulations to investigate the effect of interface structures and layer spacing on the mechanical properties of the Ti/Al nanolaminate. The results indicate that there are two transitions of the plastic deformation mechanism in the Ti layer with the increase of layer spacing in the sample with a coherent interface. The plastic deformation mechanism evolves from one that is dominated by dislocation to the phase transformation from the hcp-Ti to the fcc-Ti mode, which transfers to the dislocation slip deformation again. For the samples with an incoherent interface, the plastic deformation is dominated by the transformation from hcp-Ti to fcc-Ti, regardless of the variation of layer spacing, while the plastic deformations in the Al layers are mainly dislocations confined in the layer slip in the samples with both coherent and incoherent interfaces. When the layer spacing is larger than 6.6 nm, an obvious second hardening is observed due to the superior dislocation storage ability of the Ti/Al laminate with the incoherent interface. Meanwhile, extraordinary ductility is obtained when optimal layer spacing is employed in the Ti/Al laminate. Moreover, the phase transformation mechanism of hcp-Ti to bcc-Ti has also been explicated in the present work. The general conclusions derived from this work may provide a guideline for the design of high-performance Ti/Al multilayer and alloy devices. [ABSTRACT FROM AUTHOR]

Piezoresponse force microscopy (PFM) has emerged as the tool of choice for characterizing piezoelectric and ferroelectric materials at nanoscale, yet the interpretation of PFM remains to be difficult and sometimes ambiguous. Built on earlier works, we developed a numerical integration scheme to analyze the expected PFM response in ferroelectrics with arbitrary domain configurations, with the ultimate goal to accurately reconstruct the underlying ferroelectric structure from PFM measurements. Using such technique, we demonstrated that the relationship between the effective and intrinsic piezoelectric coefficients is sensitive to a variety of factors that are intrinsic to the probed materials, and showed that the PFM mapping is not only influenced by polarization distribution on the sample surface but also three-dimensional polarization distribution inside the material. While relatively simple domain structures were used for demonstration, the approach is general, and can be applied to ferroelectrics with arbitrary polarization distributions. [ABSTRACT FROM AUTHOR]

Thermal-induced domain wall motion of tip-inverted micro/nanodomains in near-stoichiometric LiNbO3 single crystals was investigated using piezoresponse force microscopy (PFM). The domain wall motion was observed in PFM phase and amplitude images at room temperature after the sample was subjected to a thermal process at a heating temperature higher than 100 °C. In hexagonal domains with only y walls, predetermined nucleation with layer-by-layer growth is the main mechanism for the domain wall motion. In the domains composed of both x walls and y walls, the x walls are more mobile than the y walls, and the domain wall motion starts from the random nucleation of steps along the x walls that finally grow into y walls. The domain wall motion in the near-stoichiometric LiNbO3 crystal is attributed to the energy-preferable domain wall orientation, the pyroelectric effect, and the screening charge variation caused by the thermal process. [ABSTRACT FROM AUTHOR]

Local two-way magnetoelectric (ME) couplings of a multiferroic composite have been characterized at nanoscale using novel scanning probe microscopy techniques we developed. A bilayer multiferroic composite consisting of lead zirconate titanate (PZT) and TbDyFe (TDF) has been fabricated, and the evolution of ferroelectric domains in PZT induced by an external magnetic field is observed by piezoresponse force microscopy, while the evolution of magnetic domains in TDF induced by an external electric field is observed by magnetic force microscopy, confirming the two-way ME couplings in the multiferroic composite. The technique will be useful in characterizing nanoscale ME couplings in a wide range of multiferroic composites. [ABSTRACT FROM AUTHOR]

Nanopolar structures and local ferroelectricity of Sr0.61Ba0.39Nb2O6 relaxor crystal across Curie temperature have been investigated using piezoresponse force microscopy (PFM). The short-range nanopolar clusters are dominated by long-range ferroelectric order at room temperature, but exhibit themselves at higher temperature through the morphology change in written ferroelectric domains and persisting piezoresponse beyond Curie point. A maximum piezoresponse is observed at 80 °C, which is attributed to the peak in the dielectric permittivity near the ferroelectric phase transition. Substantial asymmetry in PFM hysteresis emerges above Curie temperature, indicating an internal bias field that becomes notable in the absence of long-range ferroelectric order. [ABSTRACT FROM AUTHOR]

We investigate electronic delocalization and magnetic-flux-induced persistent current in the mesoscopic ring, which is constructed according to the nonsymmetric-dimer (NSD) model. The flux-dependent energy spectra, electronic wavefunctions, and persistent currents are theoretically obtained. It is demonstrated that due to the localization-delocalization transition of electrons, the electronic state in the NSD ring can be localized, extended, and the intermediate case between extended states and localized ones. The persistent current (PC) approaches the behavior of free electrons if the Fermi level is around the near-resonant energy. Otherwise, the PC is depressed dramatically. This conclusion could be generalized to other correlated-disordered systems. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]