Browsing by Author "Simons, H"
Now showing 1 - 7 of 7
Results Per Page
Sort Options
- ItemDomain 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, MThe 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.
- ItemElectric-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, MHigh 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
- ItemA 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, JA 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.
- ItemMeasurement 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, MThis 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.
- ItemOrigin 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, MPiezoceramics 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
- ItemTailoring 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, MThis 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.
- ItemTemperature 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, MThe 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