Browsing by Author "Jo, W"

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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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    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.