Zhiyang Wang

Electric-field-induced strain contributions in morphotropic phase boundary composition of (Bi1/2Na1/2)TiO3-BaTiO3 during poling

The microscopic contributions to the electric-field-induced macroscopic strain in a morphotropic 0.93(Bi1/2Na1/2TiO3)−0.07(BaTiO3) with a mixed rhombohedral and tetragonal structure have been quantified using full pattern Rietveld refinement of in situ high-energy x-ray diffraction data. The analysis methodology allows a quantification of all strain mechanisms for each phase in a morphotropic composition and is applicable to use in a wide variety of piezoelectric compositions. It is shown that during the poling of this material 24%, 44%, and 32% of the total macroscopic strain is generated from lattice strain, domain switching, and phase transformation strains, respectively. The results also suggest that the tetragonal phase contributes the most to extrinsic domain switching strain, whereas the lattice strain primarily stems from the rhombohedral phase. The analysis also suggests that almost 32% of the total strain is lost or is a one-time effect due to the irreversible nature of the electric-field-induce...

Electric-field-induced paraelectric to ferroelectric phase transformation in prototypical polycrystalline BaTiO3

An electric-field-induced paraelectric cubic to ferroelectric tetragonal phase transformation has been directly observed in prototypical polycrystalline BaTiO3 at temperatures above the Curie point (TC) using in situ high-energy synchrotron X-ray diffraction. The transformation persisted to a maximum temperature of 4 °C above TC. The nature of the observed field-induced transformation and the resulting development of domain texture within the induced phase were dependent on the proximity to the transition temperature, corresponding well to previous macroscopic measurements. The transition electric field increased with increasing temperature above TC, while the magnitude of the resultant tetragonal domain texture at the maximum electric field (4 kV mm−1) decreased at higher temperatures. These results provide insights into the phase transformation behavior of a prototypical ferroelectric and have important implications for the development of future large-strain phase-change actuator materials.

The effect of inter-granular constraints on the response of polycrystalline piezoelectric ceramics at the surface and in the bulk

The electro-mechanical coupling mechanisms in polycrystalline ferroelectric materials, including a soft PbZrxTi1−xO3 (PZT) and lead-free 0.9375(Bi1/2Na1/2)TiO3-0.0625BaTiO3 (BNT-6.25BT), have been studied using a surface sensitive low-energy (12.4 keV) and bulk sensitive high-energy (73 keV) synchrotron X-ray diffraction with in situ electric fields. The results show that for tetragonal PZT at a maximum electric field of 2.8 kV/mm, the electric-field-induced lattice strain (e111) is 20% higher at the surface than in the bulk, and non-180° ferroelectric domain texture (as indicated by the intensity ratio I002/I200) is 16% higher at the surface. In the case of BNT-6.25BT, which is pseudo-cubic up to fields of 2 kV/mm, lattice strains, e111 and e200, are 15% and 20% higher at the surface, while in the mixed tetragonal and rhombohedral phases at 5 kV/mm, the domain texture indicated by the intensity ratio, I111/I111¯ and I002/I200, are 12% and 10% higher at the surface than in the bulk, respectively. The obse...

A sample cell for in situ electric-field-dependent structural characterization and macroscopic strain measurements.

When studying electro-mechanical materials, observing the structural changes during the actuation process is necessary for gaining a complete picture of the structure-property relationship as certain mechanisms may be meta-stable during actuation. In situ diffraction methods offer a powerful and direct means of quantifying the structural contributions to the macroscopic strain of these materials. Here, a sample cell is demonstrated capable of measuring the structural variations of electro-mechanical materials under applied electric potentials up to 10 kV. The cell is designed for use with X-ray scattering techniques in reflection geometry, while simultaneously collecting macroscopic strain data using a linear displacement sensor. The results show that the macroscopic strain measured using the cell can be directly correlated with the microscopic response of the material obtained from diffraction data. The capabilities of the cell have been successfully demonstrated at the Powder Diffraction beamline of the Australian Synchrotron and the potential implementation of this cell with laboratory X-ray diffraction instrumentation is also discussed.

Quantitative analysis of domain textures in ferroelectric ceramics from single high-energy synchrotron X-ray diffraction images

In this study, the possibility of determining the orientation distribution function (ODF) and quantifying the domain textures of polycrystalline ferroelectrics based on single high-energy X-ray diffraction images using a Rietveld refinement method is assessed. A spherical harmonics texture model is incorporated in the approach to determine the ODFs for phase constituents in poled lead-free ferroelectric ceramics (1 − x)(Bi0.5Na0.5)TiO3 − xBaTiO3 with x = 0.0625 and 0.075 from both single high-energy synchrotron diffraction images and full rotation diffraction data collected with the samples rotated perpendicular to the poling axis. A quantitative comparison is made between the complete pole figures and pole density profiles obtained from the ODFs extracted from the different diffraction data. The results show that a good approximation to the domain textures of fiber-type in poled ceramics as determined from the full rotation data can be obtained from single diffraction images, with the dominant pole densi...