ORCID Profile
0000-0003-2138-1933
Current Organisation
Oregon State University
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Publisher: World Scientific Pub Co Pte Lt
Date: 12-2016
DOI: 10.1142/S2010135X16500326
Abstract: Ceramics of the composition BaBiO 3 (BB) were sintered in oxygen to obtain a single phase with monoclinic [Formula: see text]2/[Formula: see text] symmetry as suggested by high-resolution X-ray diffraction. X-ray photoelectron spectroscopy confirmed the presence of bismuth in two valence states — 3[Formula: see text] and 5[Formula: see text]. Optical spectroscopy showed presence of a direct bandgap at [Formula: see text] 2.2[Formula: see text]eV and a possible indirect bandgap at [Formula: see text] 0.9[Formula: see text]eV. This combined with determination of the activation energy for conduction of 0.25[Formula: see text]eV, as obtained from ac impedance spectroscopy, suggested that a polaron-mediated conduction mechanism was prevalent in BB. The BB ceramics were crushed, mixed with BaTiO 3 (BT), and sintered to obtain BT–BB solid solutions. All the ceramics had tetragonal symmetry and exhibited a normal ferroelectric-like dielectric response. Using ac impedance and optical spectroscopy, it was shown that resistivity values of BT–BB were orders of magnitude higher than BT or BB alone, indicating a change in the fundamental defect equilibrium conditions. A shift in the site occupancy of Bi to the A-site is proposed to be the mechanism for the increased electrical resistivity.
Publisher: Informa UK Limited
Date: 02-01-2017
Publisher: Springer Science and Business Media LLC
Date: 11-02-2016
DOI: 10.1038/SREP20829
Abstract: Structure-property relationships in ferroelectrics extend over several length scales from the in idual 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 BaTiO 3 -BiZn 0.5 Ti 0.5 O 3 (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.
Publisher: AIP Publishing
Date: 27-07-2020
DOI: 10.1063/5.0013410
Abstract: Changes in the polarization state of ferroelectric materials are mediated through the motion of planar defects such as domain walls. The interplay between the two processes that enable the inversion of the macroscopic polarization in ferroelectric materials, non-180° (domain reorientation) and 180° (domain reversal), is not well understood. In this work, time-resolved x-ray diffraction was carried out during the application of an external electric field to investigate the dynamic electric-field response mechanisms of BaTiO3 (BT) and BiZn1/2Ti1/2O3(BZT)-modified BT (0.94BT-0.06BZT). These data evidence that the incorporation of BZT into BT fundamentally alters what processes are activated to reorient the polarization by 180°. Polarization reversal in BT is achieved through direct inversion of spontaneous dipoles. However, the addition of BZT into BT promotes a two-step polarization reversal process (i.e., two consecutive non-180° reorientation events).
Publisher: Springer Science and Business Media LLC
Date: 23-05-2013
Publisher: Elsevier BV
Date: 08-2017
Publisher: Springer Science and Business Media LLC
Date: 07-07-2016
Publisher: Wiley
Date: 08-01-2018
DOI: 10.1111/JACE.15403
Publisher: Elsevier BV
Date: 03-2018
Location: United States of America
Location: United States of America
No related grants have been discovered for David Cann.