Browsing by Author "Hoffman, M"

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    Assessment of radioactive ‘Hot Particles’ and marine sediment plutonium and americium levels from the Montebello Islands, Western Australia
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Hoffman, M; Johansen, MP; Cook, M; Howell, NR; Kleinschmidt, R; Clegg, JK
    The Montebello islands are an archipelago off the Western Australian coast that to this day display an artificial radioactive legacy. The legacy is the result of nuclear testing from 1952-1956. that produced long-lived radionuclides such as americium (Am-241) and plutonium (Pu-239/240). This study investigated the extent and characteristics of radioactive contamination in marine sediments near the former Operation Hurricane and Operation Mosaic G2 detonation sites in hopes of contributing to future management strategies and updated assessment of health risks to native flora, fauna and human populations. The project was conducted with samples collected in 2015 by the Australian Nuclear Science and Technology Organisation (ANSTO) as two series; Series 1 chosen to monitor the activity from the Operation Mosaic G2 detonation and Series 2 aiming to determine residual activity from the Operation Hurricane HMS Plymouth detonation. Samples were initially sieved to separate the bulk samples into four size-based fractions for analysis of activity fractionation among sediment grain sizes. Radiation counting processes included alpha spectrometry and gamma spectrometry, back-scatter electron mode scanning electron microscopy (BEI-SEM) and photo-stimulated luminescent (PSL) autoradiography to evaluate the overall radiative status of the sediment locations and to investigate the presence of ‘hot’ particles or heterogenous dispersion of radioactivity. Both spectrometry processes revealed that Series 1 Am-241 and Pu-239/240 activity was dispersed preferentially in the two larger fractions (>500 um and 500-200 um). Activity determined as Am241 and Pu-289/240 vi/as observed across Series 2 as well but as values an order of magnitude lower. Environmental plutonium from Series 1 was present in hot particle form, specifically within particles from the more active >500 um [largest] fraction which revealed gamma emissions of the plutonium progeny Am241. imaging and subsequent analysis by BE!-SEM and energy dispersive X-ray spectroscopy (EDS) of the particles revealed that the majority of the particle material was calcium carbonate, indicative of the dominant geology at the detonation site. Study results provide insights into the radioactive characteristics of hot-particles and bulk sediments at the Montebello site. it is believed and hoped that this investigation will aid decisions on the future management of the Montebello wildlife resources and marine park management, and provide insights into potential risks and protective measures for site visitors and researchers.
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    Determining fundamental properties from diffraction: electric field induced strain and piezoelectric coefficient
    (Australian Institute of Physics, 2016-02-04) Hinterstein, M; Studer, AJ; Hoffman, M
    Piezoelectric ceramics exhibit the remarkable property to couple elastic strain and polarization under the influence of an applied electric field. Among the various types of piezoelectric devices, especially actuators rely on high electric fields to generate high strains and forces. Prominent examples for actuators are multilayer stack actuators used for nanopositioning or in modern combustion engines for automobiles to control injection cycles. The two most important characteristics of this class of materials are macroscopic strain and piezoelectric coefficient. Despite extensive studies and elaborated measurement techniques, the correlation between macroscopic strain and structural response is still not fully understood. Most of the relevant systems found up to now are compositions close to phase boundaries linking highly correlated phases. This results in major challenges for structural analyses due to overlapping reflections. Apart from the well-known field induced structural responses such as domain switching and the converse piezoelectric effect we recently identified field induced phase transitions in different systems as an additional poling mechanism. In order to resolve all three involved poling mechanisms within only one experiment we developed a structural analysis technique with in situ X-ray and neutron powder diffraction data. The results not only separately reveal the contributions of each poling mechanism to the macroscopic strain, but also different behaviours of the individual phases. The calculation of the elastic strain perfectly matches the macroscopic observations, confirming the accuracy of the applied models. Since this method yields fundamental information such as the crystal structure as a function of applied electric field, we were able to calculate the piezoelectric coefficient for the individual phases based on information on the atomic scale. In this contribution we present the latest research on the elucidation of strain mechanisms and fundamental properties in piezoceramics.
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    Domain fragmentation during cyclic fatigue in 94%Bi(1/2)Na(1/2)TiO3-6%BaTiO3.
    (American Institute of Physics, 2012-01-01) Simons, H; Glaum, J; Daniels, JE; Studer, AJ; Liess, A; Rodel, J; Hoffman, M
    The fatigue of the lead-free piezoceramic 94%(Bi1/2Na1/2)TiO3-6%BaTiO3 was investigated under bipolar electric fields. Degradation of the polarization, strain, and permittivity was measured during the fatigue process, and correlated with structural data measured at incremental points in the fatigue process using neutron diffraction. The results suggest a two-stage fatigue mechanism whereby, following a field-induced phase transformation to a poled ferroelectric state, the domain structure becomes progressively fragmented by a repetitive process of domain wall pinning and subdivision. © 2012, American Institute of Physics.
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    Electric-field-induced strain mechanisms in lead-free 94%(Bi1/2Na1/2)TiO3–6%BaTiO3.
    (American Institute of Physics, 2011-02-21) Simons, H; Daniels, JE; Jo, W; Dittmer, R; Studer, AJ; Avdeev, M; Rodel, J; Hoffman, M
    High resolution neutron diffraction has been used to investigate the structural origin of the large electric-field-induced remanent strain in 94(Bi1/2Na1/2)TiO3–6BaTiO3 ceramics. The virgin material was found to be a mixture of near-cubic phases with slight tetragonal and rhombohedral distortions of a0a0c+ and a−a−a− octahedral tilt type, respectively. Application of an electric field of 4.57 kV/mm transformed the sample to a predominantly rhombohedral a−a−a− modification with a significantly higher degree of structural distortion and a pronounced preferred orientation of the c-axis along the field direction. These electric field-induced structural effects contribute significantly to the macroscopic strain and polarization of this system. © 2011, American Institute of Physics
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    Ferroelastic contribution to the piezoelectric response in lead zirconate titanate by in situ stroboscopic neutron diffraction
    (Elsevier B. V., 2006-11-15) Jones, JL; Hoffman, M; Daniels, JE; Studer, AJ
    Ferroelastic domain switching during dynamic actuation is measured in situ for a piezoelectric lead zirconate titanate (PZT) ceramic utilizing a new capability developed on The Australian Strain Scanner (TASS) at ANSTO. Diffraction patterns are obtained as a function of time during a 1 Hz cycle. The change in the 0 0 2 and 2 0 0 diffraction intensities indicates there is ferroelastic domain switching at sub-coercive (weak) fields. © 2006 Elsevier B.V.
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    Ferroelastic domain switching fatigue in lead zirconate titanate ceramics
    (Elsevier, 2008-04) Pojprapai, S; Jones, JL; Studer, AJ; Russell, J; Valanoor, N; Hoffman, M
    The influence of the frequency and amplitude of cyclic mechanical loading on soft, tetragonal lead zirconate titanate (PZT) ceramics was investigated via neutron diffraction. Intensity change in the {2 0 0} reflections provided quantitative measurements of domain switching behavior, domain texture and the strain resulting from domain switching. The results are explained using a viscoelasticity model. It was found that the magnitude of applied stress affects the level of strain accumulated, while its frequency affects the time taken for the strain to reach saturation. Furthermore, markedly different behaviors are exhibited by poled and unpoled samples. For samples loaded under identical conditions, the frequency effect is more pronounced in unpoled samples and the accumulated ferroelastic strain is greater in poled samples. © 2008, Elsevier Ltd.
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    A high-temperature-capacitor dielectric based on K0.5Na0.5NbO3-Modified Bi1/2Na1/2TiO3–Bi1/2K1/2TiO3
    (Wiley-Blackwell, 2012-11-01) Dittmer, R; Anton, EM; Jo, W; Simons, H; Daniels, JE; Hoffman, M; Pokorny, J; Reaney, IM; Rödel, J
    A high-temperature dielectric, (1–x)(0.6Bi1/2Na1/2TiO3–0.4Bi1/2K1/2TiO3)–xK0.5Na0.5NbO3, off the morphotropic phase boundary of the parent matrix 0.8Bi1/2Na1/2TiO3–0.2Bi1/2K1/2TiO3, has been developed for application as a high-temperature capacitor. In addition to temperature-dependent permittivity and dielectric loss, DC conductivity and field-dependent permittivity are reported. These properties are correlated with temperature-dependent structure data measured at different length scales using Raman spectroscopy and neutron diffraction. It is suggested that all materials investigated are ergodic relaxors with two types of polar nanoregions providing different relaxation mechanisms. The most attractive properties for application as high-temperature dielectrics are obtained in a material with x = 0.15 at less than 10% variation of relative permittivity of about 2100 between 54°C and 400°C. © 2012, Wiley-Blackwell.
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    Intrinsic and extrinsic contributions to the piezoelectric effect in soft lead zirconate titanate (PZT) ceramics by time-resolved neutron diffraction
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Jones, JL; Daniels, JE; Studer, AJ; Hoffman, M; Finlayson, TR
    Piezoelectric ceramics are used in biomedical, naval, micromechanical, and many other precision engineering applications and therefore require a well-characterized, stable response. Utilizing a new capability developed on the The Australian Strain Scanner (TASS) at ANSTO, we have directly measured in situ the intrinsic and extrinsic t contributions to the piezoelectric effect in soft lead zirconate titanate (PZT) ceramics. The 002 and 200 diffraction peaks are measured as a function of time using a stroboscopic technique which enables timing resolutions of less than 30us. In other words, we have measured the 200 and 002 peak profiles as a function of time during piezoelectric activation. In this tetragonal crystal structure, a comparison of the 002 and 200 integrated intensity yields the non-180° domain switching contribution (extrinsic) while shifting of the peaks yields the change in 001 and 100 lattice strains (intrinsic). Both components lead to the macroscopic strain measured as the piezoelectric response, which is found to be a function of frequency and applied electric field. These results go toward explaining the nonlinearities of piezoelectric response versus frequency and magnitude of driving field measured in earlier work. © The Authors
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    Measurement and analysis of field-induced crystallographic texture using curved position-sensitive diffraction detectors
    (Springer Nature, 2014-02-09) Simons, H; Daniels, JE; Studer, AJ; Jones, JL; Hoffman, M
    This paper outlines measurement and analysis methodologies created for determining the structural responses of electroceramics to an electric field. A sample stage is developed to apply electric fields to ceramic materials at elevated temperatures during neutron diffraction experiments. The tested voltages and temperatures range from −20 kV to +20 kV and room temperature to 200 °C, respectively. The use of the sample environment for measuring the response of ferroelectric ceramics to an electrical stimulus is demonstrated on the instrument Wombat, a monochromatic neutron diffractometer employing a curved positive sensitive detector. Methodologies are proposed to account for the geometrical effects when vector fields are applied to textured materials with angularly dispersive detector geometries. Representative results are presented for the ferroelectric (Bi1/2Na1/2)TiO3-6%BaTiO3 (BNT-6BT) which show both phase transformation and ferroelectric domain texturing under the application of an electric field. This experimental and analysis approach is well suited for time-resolved measurements such as stroboscopic and in situ studies on a variety of electro-active materials.© 2014, Springer Science+Business Media New York.
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    Neutron diffraction study of the polarization reversal mechanism in [111](c)-oriented Pb(Zn1/3Nb2/3)O-3-xPbTiO(3).
    (American Institute of Physics, 2007-05-24) Daniels, JE; Finlayson, TR; Davis, M; Damjanovic, D; Studer, AJ; Hoffman, M; Jones, JL
    The polarization reversal mechanism in [111](c)-oriented Pb(Zn1/3Nb2/3)O-3-xPbTiO(3) has been investigated by in-situ neutron diffraction. Stepwise static-field measurements of the (222)(c) rocking curves confirm a two-stage polarization reversal mechanism via a sequence of non-180 degrees domain reorientations. The time-resolved response has also been measured upon application of a bipolar square wave with a 30 s period to observe directly the relaxation times of diffracted neutron intensity during the reversal process. Upon application of a large antipolar field, the diffraction intensity increases quickly, before relaxing over a longer time period with an exponential decay constant, tau, of approximately 5.7 s. These large time constants correlate with a frequency dependence of the macroscopic strain-field response. © 2007, American Institute of Physics
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    Origin of large recoverable strain in 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 near the ferroelectric-relaxor transition
    (America Institute of Physics, 2013-02-11) Simons, H; Daniels, JE; Glaum, J; Studer, AJ; Jones, JL; Hoffman, M
    Piezoceramics of composition 0.94(Bi(0.5)Na(0.5))TiO(3)-0.06BaTiO(3) demonstrate large recoverable strain at elevated temperature (T > 75 degrees C), which is absent at room temperature. In situ neutron diffraction was used to measure changes in the crystallographic and domain structures during electric field application at temperatures ranging from 25 degrees C to 100 degrees C. Quantitative evaluation of the ferroelastic domain volume fraction in the field-induced phases enabled calculation of the strain contribution from non-180 degrees domain switching. The large recoverable strain is shown to be associated with the reversible nature of the phase transformation. These findings have implications to additional BNT-xBT-based composition and other relaxor ferroelectrics. © 2013, American Institute of Physics
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    Tailoring the piezoelectric and relaxor properties of (Bi1/2Na1/2)TiO3-BaTiO3 via zirconium doping
    (John Wiley and Sons, 2013-04-25) Glaum, J; Simons, H; Acosta, M; Hoffman, M
    This article details the influence of zirconium doping on the piezoelectric properties and relaxor characteristics of 94(Bi1/2Na1/2)TiO3–6Ba(ZrxTi1−x)O3 (BNT–6BZT) bulk ceramics. Neutron diffraction measurements of BNT–6BZT doped with 0%–15% Zr revealed an electric-field-induced transition of the average crystal structure from pseudo-cubic to rhombohedral/tetragonal symmetries across the entire compositional range. The addition of Zr up to 10% stabilizes this transition, resulting in saturated polarization hysteresis loops with a maximum polarization of 40 μC/cm2 at 5.5 kV/mm, while corresponding strain hysteresis measurements yield a maximum strain of 0.3%. With further Zr addition, the ferroelectric order is progressively destabilized and typical relaxor characteristics such as double peaks in the current density loops are observed. In the strain hysteresis, this destabilization leads to an increase of the maximum strain by 0.05%. These changes to the physical behavior caused by Zr addition are consistent with a reduction of the transition temperature TF-R, above which the field-induced transformation from the relaxor to ferroelectric state becomes reversible. © 2013, The American Ceramic Society.
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    Temperature and magnetic field dependent magnetization of nanoparticulate ZnFe2O4 produced by mechanochemical synthesis
    (Australian Institute of Nuclear Science and Engineering, 2016-02-02) Nesa, F; Wang, X; Wang, JL; Kennedy, SJ; Campbell, SJ; Hoffman, M
    ZnFe2O4 is basically a non-inverted ferrite which is enormously used as ferrofluids, magnetoelectric refrigeration and contrast agent for magnetic resonance imaging. A series of nanoparticulate ZnFe2O4 of average sizes F ~ 9 nm to 90 nm with a range of inversion 0.008 to 0.35 has been produced by mechanochemical synthesis. The blocking temperature of the investigated samples has increased with increasing crystallite size and accordingly behaved as Curie-Weiss paramagnetic materials. The temperature dependent magnetic behavior of these nanoparticulates has been investigated over the temperature range from 5 K to 300 K at a magnetic field of 100 oe. DC magnetization over a magnetic field range of 0 oe to 10000 oe at 5 K, 150 K and 200 K has been observed which interpreted that the samples are superparamagnetic materials. All the samples showed the normal magnetic hysteresis below blocking temperature which also shows that the coercively increases with decreasing inversion 1. The frequency dependent magnetic behaviour of nanoparticulate ZnFe2O4 of 90 nm crystallite size has also been studied over a frequency range of 10 Hz to 10000 Hz which interpreted that with the increase of frequency the magnetization of this sample increased to saturation magnetization for all samples are approximately at 100 K temperature.
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    Temperature dependence on domain switching behavior in lead zirconate titanate under electrical load via in situ neutron diffraction
    (Wiley-Blackwell, 2011-10-01) Pojprapai, S; Simons, H; Studer, AJ; Luo, ZH; Hoffman, M
    The influence of temperature on the kinetics of domain switching in lead zirconate titanate was investigated by using in situ neutron diffraction. Samples were electrically loaded to 1 kV/mm at 30°C, 125°C, and 175°C, after which the diffracted patterns in the on- and off-state were compared. The results demonstrated that the degree of domain switching increases with increased temperature. Corroboration with hysteresis measurements showed that while the coercive field decreases with increasing temperature, the degree of saturation increased significantly. According to Merz's model, it is therefore apparent that, due to increased switching rate at high temperature, domain switchability increases with temperature. © 2011, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
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    Time-resolved diffraction measurements of electric-field-induced strain in tetragonal lead zirconate titanate
    (American Institute of Physics, 2007-05-01) Daniels, JE; Finlayson, TR; Studer, AJ; Hoffman, M; Jones, JL
    The dynamic electric-field-induced strain in piezoelectric ceramics enables their use in a broad range of sensor, actuator, and electronic devices. In piezoelectric ceramics which are also ferroelectric, this macroscopic strain is comprised of both intrinsic (piezoelectric) and extrinsic (non-180 degrees domain switching) strain components. Extrinsic contributions are accompanied by hysteresis, nonlinearity, and fatigue. Though technologically significant, direct measurement of these mechanisms and their relative contributions to the macroscopic response has not yet been achieved at driving frequencies of interest. Here we report measurements of these mechanisms in ceramic lead zirconate titanate during application of subcoercive cyclic driving electric fields using an in-situ stroboscopic neutron diffraction technique. Calculations are made from the diffraction measurements to determine the relative contributions of these different strain mechanisms. During applied electric field square waves of +0.5E(c) unipolar and +/- 0.5E(c) bipolar, at 1 Hz, non-180 degrees domain switching is found to contribute 34% and 40% of the macroscopically measured strain, respectively. © 2007, American Institute of Physics