Structure-property relationships in ferroelectrics extend over several length scales from the individual unit cell to the macroscopic device, and with dynamics spanning a broad temporal domain. ...Characterizing the multi-scale structural origin of electric field-induced polarization reversal and strain in ferroelectrics is an ongoing challenge that so far has obscured its fundamental behaviour. By utilizing small intensity differences between Friedel pairs due to resonant scattering, we demonstrate a time-resolved X-ray diffraction technique for directly and simultaneously measuring both lattice strain and, for the first time, polarization reversal during in-situ electrical perturbation. This technique is demonstrated for BaTiO3-BiZn0.5Ti0.5O3 (BT-BZT) polycrystalline ferroelectrics, a prototypical lead-free piezoelectric with an ambiguous switching mechanism. This combines the benefits of spectroscopic and diffraction-based measurements into a single and robust technique with time resolution down to the ns scale, opening a new door to in-situ structure-property characterization that probes the full extent of the ferroelectric behaviour.
Exciting a ferromagnetic material with an ultrashort IR laser pulse is known to induce spin dynamics by heating the spin system and by ultrafast spin diffusion processes. Here, we report on ...measurements of spin-profiles and spin diffusion properties in the vicinity of domain walls in the interface region between a metallic Al layer and a ferromagnetic Co/Pd thin film upon IR excitation. We followed the ultrafast temporal evolution by means of an ultrafast resonant magnetic scattering experiment in surface scattering geometry, which enables us to exploit the evolution of the domain network within a 1/e distance of 3 nm to 5 nm from the Al/FM film interface. We observe a magnetization-reversal close to the domain wall boundaries that becomes more pronounced closer to the Al/FM film interface. This magnetization-reversal is driven by the different transport properties of majority and minority carriers through a magnetically disordered domain network. Its finite lateral extension has allowed us to measure the ultrafast spin-diffusion coefficients and ultrafast spin velocities for majority and minority carriers upon IR excitation.
This article reports on energy‐dispersive micro Laue (µLaue) diffraction of an individual gold nanowire that was mechanically deformed in three‐point bending geometry using an atomic force ...microscope. The nanowire deformation was investigated by scanning the focused polychromatic X‐ray beam along the nanowire and recording µLaue diffraction patterns using an energy‐sensitive pnCCD detector that permits measurement of the angular positions of the Laue spots and the energies of the diffracted X‐rays simultaneously. The plastic deformation of the nanowire was shown by a bending of up to 3.0 ± 0.1°, a torsion of up to 0.3 ± 0.1° and a maximum deformation depth of 80 ± 5 nm close to the position where the mechanical load was applied. In addition, extended Laue spots in the vicinity of one of the clamping points indicated the storage of geometrically necessary dislocations with a density of 7.5 × 1013 m−2. While µLaue diffraction with a non‐energy‐sensitive detector only gives access to the deviatoric strain, the energy sensitivity of the employed pnCCD offers absolute strain measurements with a resolution of 1%. Here, the residual strain after complete unloading of the nanowire amounted to maximum tensile and compressive strains of the order of +1.2 and −3%, which is comparable to the actual resolution limit. The combination of white‐beam µLaue diffraction using an energy‐sensitive pixel detector with nano‐mechanical testing opens up new possibilities for the study of mechanical behavior at the nanoscale.
This article reports on energy‐dispersive micro Laue (µLaue) diffraction of an individual gold nanowire that was mechanically deformed in three‐point bending geometry using an atomic force microscope. The nanowire deformation was investigated by scanning the focused polychromatic X‐ray beam along the nanowire and recording µLaue diffraction patterns using an energy‐sensitive pnCCD detector that permits measurement of the angular positions of the Laue spots and the energies of the diffracted X‐rays simultaneously.
In this paper, a novel method to quantify the incubation of damage on piezoelectric crystal is presented. An intrinsic length scale parameter obtained from nonlocal field theory is used as a novel ...measure for quantification of damage precursor. Features such as amplitude decay, attenuation, frequency shifts and higher harmonics of guided waves are commonly-used damage features. Quantification of the precursors to damage by considering the mentioned features in a single framework is a difficult proposition. Therefore, a nonlocal field theory is formulated and a nonlocal damage index is proposed. The underlying idea of the paper is that inception of the damage at the micro scale manifests the evolution of damage at the macro scale. In this paper, we proposed a nonlocal field theory, which can efficiently quantify the inception of damage on piezoelectric crystals. The strength of the method is demonstrated by employing the surface acoustic waves (SAWs) and longitudinal bulk waves in Lithium Niobate (LiNbO3) single crystal. A control damage was introduced and its manifestation was expressed using the intrinsic dominant length scale. The SAWs were excited and detected using interdigital transducers (IDT) for healthy and damage state. The acoustic imaging of microscale damage in piezoelectric crystal was conducted using scanning acoustic microscopy (SAM). The intrinsic damage state was then quantified by overlaying changes in time of flight (TOF) and frequency shift on the angular dispersion relationship.
► V(z) curves are generated for PZT using acoustic microscopy. ► Longitudinal, shear and surface wave velocity are determined. ► SEM is conducted on PZT material for grain size distribution and ...morphology.
Lead Zirconate Titanate (PZT) is a piezo-electric ceramic material that needs to be characterized for its potential use in microelectronics. Energy dispersive X-ray analysis (EDX) is conducted to determine the chemical composition of the PZT ceramics. The scanning electron microscope (SEM) is performed to study the surface morphology, grain structure and grain boundaries. The SEM image helps us to understand the surface wave propagation and scattering phenomena by the PZT and the reason for its anisotropy and inhomogeneity due to the grain structure. In this paper scanning acoustic microscopy at 100MHz excitation frequency is conducted for determining mechanical properties of PZT. Earlier works reported only the longitudinal wave speed in PZT while in this paper longitudinal, shear and surface acoustic wave speeds of sintered PZT are measured from its acoustic material signature (AMS) curves, also known as V(z) curves. AMS or V(z) curve is the variation of the output voltage as a function of the distance between the acoustic lens focal point and the reflecting surface. The average velocities of longitudinal, shear and surface acoustic waves in a PZT specimen are determined from its V(z) curve generated at 100MHz excitation frequency and found to be over 5000m/s, over 3000m/s and between 2500 and 3000m/s, respectively. From these velocities all elastic constants of the specimen are obtained.
•Phase and grain boundaries are barriers to VHCF crack propagation.•Barrier efficiency depends on slip geometry of neighboring grains.•The first barrier decides if duplex stainless steel exhibits a ...real fatigue limit.•Barrier efficiencies can be implemented in the finite element method.
During VHCF loading of duplex steels fatigue damage starts within the softer austenite phase. Depending on the spatial mismatch between the slip systems of neighboring grains, intergranular or transgranular fatigue cracks are initiated. If these cracks can propagate or are blocked depends on the interactions with the local microstructure. These interactions have been studied by ultrasonic fatigue testing in combination with electron microscopy and synchrotron diffraction experiments. It was found that the strength of the first microstructural barrier is decisive for VHCF life. The barrier strength as a function of the microstructural arrangement has been implemented in a micromechanical finite element approach that shall be used to predict the VHCF life or the existence of a fatigue limit for given microstructure parameters.
PDF
