ORCID Profile
0000-0001-7039-7857
Current Organisation
University of New South Wales
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
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: 12-02-2018
Publisher: Elsevier BV
Date: 2018
Publisher: AIP Publishing
Date: 13-07-2020
DOI: 10.1063/5.0013248
Abstract: Similar to several Pb-based relaxor ferroelectrics, 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 is reported to have a micrometer-sized surface layer. We hypothesize that since this layer has structural properties distinct from the bulk, it would undergo a different property degradation than the bulk during cyclic electrical loading or fatigue. First, we show the existence of a surface layer by comparing X-ray diffraction patterns of the ceramic surface and powders. Then, we show that fatigue damage is mainly localized in the surface layers, and thus, property degradation due to fatigue can be recovered on removing the affected surface layer. We also show that ion migration may be occurring in the surface layer during fatigue experiments using secondary ion mass spectroscopy, where the ion sources may be the s le itself, the electrode layer or the insulating oil in which the experiment is performed. Finally, we show that permanent fatigue damage such as microcracks is dependent on the choice of electrodes. While permanent damage was observed for Pt electrodes, it was not present for oxide electrodes, suggesting that oxygen permeation and accumulation at the electrode/surface interface may play a role in the formation of observed microcracks. In summary, we have shown that fatigue is influenced by the surface layer, and surface layer damage can be controlled using the selection of electrodes.
Publisher: Elsevier BV
Date: 08-2017
Publisher: Elsevier BV
Date: 02-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0TC01300E
Abstract: We demonstrate a unique capability to control the formation and properties of skin layer structures in relaxor ferroelectrics by adjusting defect concentration. It is shown that the skin layer is polar and both electrically and optically active.
Publisher: Springer Science and Business Media LLC
Date: 07-07-2016
Publisher: Elsevier BV
Date: 03-2018
Publisher: Wiley
Date: 06-05-2019
Publisher: Elsevier BV
Date: 08-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9TC05665C
Abstract: The reduction of degradation rate at high cycles indicates the subsequent contribution from micro-scale surface damage, leading to irreversible fatigue.
Publisher: Informa UK Limited
Date: 02-01-2017
Publisher: AIP Publishing
Date: 16-03-2022
DOI: 10.1063/5.0080924
Abstract: The method of generating x-rays using the pyroelectric effect has garnered interest for applications that desire portability and low power consumption, particularly for real-time in-field and on-line analyses. However, the x-ray intensity produced by this type of x-ray generator is low and inconsistent compared to conventional x-ray tubes. The properties of several pyroelectric materials, including LiTaO3, LiNbO3, and PMN-xPT, were studied and subsequently tested on an in-house developed x-ray generator to explore their suitability for the application. The production of electrons to subsequently generate x-ray relies on the process of ferroelectric electron emission and field ionization to be dominant over charge compensation via the DC conductivity of the pyroelectric material. Given that the time of temperature change occurs faster than the material's charge relaxation time, it was found that the ratio of the pyroelectric coefficient to relative permittivity determined the performance of the x-ray generator. Thus, the x-ray count rates and end-point energies produced by LiTaO3 showed that it continues to be a strong candidate for such x-ray generation applications.
Publisher: Wiley
Date: 17-04-2019
DOI: 10.1111/JACE.16475
Publisher: Wiley
Date: 08-01-2018
DOI: 10.1111/JACE.15403
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8TC04189J
Abstract: Addition of KNN to BNT–BT moves the phase diagram to lower temperatures while introduced oxygen vacancies move it to higher temperatures.
Publisher: Wiley
Date: 25-01-2021
DOI: 10.1111/JACE.17625
Abstract: The fracture properties of 0.94(Na 0.5 Bi 0.5 )TiO 3 ‐0.06BaTiO 3 (NBT‐6BT) relaxor ferroelectrics were investigated using the Vickers indentation method and computation of crack tip opening displacement. It was found that an unpoled s le had a fracture toughness of around 1.35 MPa m 1/2 . In contrast, an electrically poled s le exhibited anisotropy with a lower fracture toughness perpendicular to the poling direction and a higher value in the parallel direction, as compared to the unpoled s le. Upon cyclic electrical loading (with applied electric field litudes between 0.73 E C and 1.4 E C ), the indented surface crack was found to propagate. In general, the crack grew rapidly during the initial cycles followed by crack arrest, and the principal driving force for crack growth was proposed to be residual stress around the indentation, as evidenced by the limited field dependence of crack growth. There was also a contribution from the electromechanical strain, which played a role at high cycles ( cycles) and high fields ( .3 E C ). Evidence of a saturation threshold of crack propagation is an advantage for the electromechanical reliability of relaxor ferroelectrics in devices.
No related grants have been discovered for Nitish Kumar.