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Instruments / Technical Area	Publication Details	Published
I15-Extreme Conditions	Domain switching and shear-mode piezoelectric response induced by cross-poling in polycrystalline ferroelectrics D. A. Hall , L. Daniel , M. Watson , A. Condie , T. P. Comyn , A. K. Kleppe , P. J. Withers Journal Of Applied Physics 136 DOI: 10.1063/5.0238994 Diamond Proposal Number(s): [8699] Open Access Show Abstract ▼ Abstract: The mechanisms contributing to the electromechanical response of piezoelectric ceramics in shear mode have been investigated using high energy synchrotron x-ray diffraction. Soft lead zirconate titanate ceramic specimens were subjected to an electric field in the range 0.2 to 3.0 MV m-1, perpendicular to that of the initial poling direction, while XRD patterns were recorded in transmission. At low electric field levels, the axial strains remained close to zero but a significant shear strain occurred due to the reversible shear-mode piezoelectric coefficient. Both the axial and shear strains increased substantially at higher field levels due to irreversible ferroelectric domain switching. Eventually, the shear strain decreased again as the average remanent polarization became oriented towards the electric field direction. The lattice strain and domain orientation distributions follow the form of the total strain tensor, enabling the domain switching processes to be monitored by the rotation of the principal strain axis. Reorientation of this axis towards the electric field direction occurred progressively above 0.6 MV m-1, while the angle of rotation increased from 0° to approximately 80° at the maximum field of 3.0 MV m-1. A strong correlation was established between the effective strains associated with different crystallographic directions, which was attributed to the effects of elastic coupling between grains in the polycrystal.	Nov 2024
I15-Extreme Conditions	Temperature-dependent ferroelectric properties and aging behavior of freeze-cast bismuth ferrite–barium titanate ceramics Bastola Narayan , Zihe Li , Bing Wang , Astri Bjørnetun Haugen , David Hall , Hamideh Khanbareh , James Roscow Acs Applied Materials & Interfaces DOI: 10.1021/acsami.4c03002 Diamond Proposal Number(s): [34299] Open Access Show Abstract ▼ Abstract: Lead-free BiFeO3–BaTiO3 (BF-BT) piezoceramics have sparked considerable interest in recent years due to their high piezoelectric performance and high Curie temperature. In this paper, we show how the addition of highly aligned porosity (between 40 and 60 vol %) improves the piezoelectric performance, sensing, and energy harvesting figures of merit in freeze-cast 0.70BiFeO3–0.30BaTiO3 piezoceramics compared to conventionally processed, nominally dense samples of the same composition. The dense and porous BF-BT ceramics had similar longitudinal piezoelectric coefficients (d33) immediately after poling, yet the dense samples were observed to age faster than those of porous ceramics. After 24 h, for example, the porous samples had significantly higher d33 values ranging from 112 to 124 pC/N, compared to 85 pC/N for the dense samples. Porous samples exhibited 3 and 5 times higher longitudinal piezoelectric voltage coefficient g33 and energy harvesting figure of merit d33g33 than dense samples due to the unexpected increase in d33 and decrease in relative permittivity with porosity. Spontaneous polarization (Ps) and remnant polarization (Pr) decrease as the porosity content increased from 37 to 59 vol %, as expected due to the lower volume of active material; however, normalized polarization values with respect to porosity level showed a slight increase in the porous materials relative to the dense BF-BT. Furthermore, the porous ceramics showed improved temperature-dependent strain–field response compared to the dense. As a result, these porous materials show excellent potential for use in high temperature sensing and harvesting applications.	Apr 2024
I15-Extreme Conditions	Acceptor doping and actuation mechanisms in Sr-doped BiFeO3BaTiO3 ceramics Ziqi Yang , Yizhe Li , Bing Wang , Juncheng Pan , Annette K. Kleppe , David Hall Journal Of Materiomics 71 DOI: 10.1016/j.jmat.2023.04.007 Diamond Proposal Number(s): [30553] Open Access Show Abstract ▼ Abstract: BiFeO3-BaTiO3 (BF-BT) ceramics are important multiferroic materials, which are attracting significant attention for potential applications in high temperature lead-free piezoelectric transducers. In the present study, the effects of Sr2+ as an acceptor dopant for Bi3+, in the range from 0 to 1.0 at%, on the structure and ferroelectric/piezoelectric properties of 0.7BiFeO3-0.3BaTiO3 ceramics were evaluated. The use of a post-sintering Ar annealing process was found to be an effective approach to reduce electrical conductivity induced by the presence of electron holes associated with reoxidation during cooling. A low Sr dopant concentration (0.3 at %) yielded enhanced ferroelectric (Pmax ~ 0.37 C m-2, Pr ~ 0.30 C m-2) and piezoelectric (d33 ~ 178 pC N-1, kp ~ 0.27) properties, whereas higher levels led to chemically heterogeneous core-shell structures and secondary phases with an associated decline in performance. The electric field-induced strain of the Sr-doped BF-BT ceramics was investigated using a combination of digital image correlation macroscopic strain measurements and in-situ synchrotron X-ray diffraction. Quantification of the intrinsic (lattice strain) and extrinsic (domain switching) contributions to the electric field induced strain indicated that the intrinsic contribution dominated during the poling process.	May 2023

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