Browsing by Author "Guo, YP"

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    A correlated electron diffraction, in situ neutron diffraction and dielectric properties investigation of poled (1-x)Bi0.5Na0.5TiO3-xBaTiO3 ceramics
    (American Institute of Physics, 2011-10-15) Wang, J; Liu, Y; Withers, RL; Studer, AJ; Li, Q; Norén, L; Guo, YP
    A correlated electron diffraction, temperature-dependent in situ neutron diffraction, and temperature-dependent dielectric properties investigation of poled (1-x)Bi(0.5)Na(0.5)TiO(3)-xBaTiO(3) (BNTBT100x) (x = 0.04, 0.07, and 0.12) samples has been carried out. The results show that the depolarization temperature, T(d), of the rhombohedral BNTBT 4 sample is associated with the disappearance of G +/- 1/2 [111]*(p) satellite reflections and a(-)a(-)a(-) octahedral tilting while that of the BNTBT 12 sample is associated with a metrically tetragonal to metrically cubic or pseudo-cubic symmetry. In the case of the poled BNTBT 7 sample in the MPB region, the dielectric properties show a quite distinct two stage transition from a room temperature clearly metrically tetragonal phase again to a metrically cubic or pseudo-cubic symmetry above 150 degrees C. There is no apparent change in its average structure in vicinity of T(d) in BNTBT 7. Electron diffraction shows the presence of considerable octahedral tilt twin disorder in all three samples. (C) 2011 American Institute of Physics.
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    Response of intergrown microstructure to an electric field and its consequences in the lead-free piezoelectric bismuth sodium titanate
    (Elsevier, 2012-03) Liu, Y; Norén, L; Studer, AJ; Withers, RL; Guo, YP; Li, YX; Yang, H; Wang, J
    We investigate the R3c average structure and micro-structure of the ceramic Bi 0.5Na 0.5TiO 3 (BNT) in situ under applied electric fields using diffraction techniques. Electron diffraction implies the presence of significant octahedral tilt twin disorder, corresponding to the existence of a fine scale intergrown microstructural (IGMS) 'phase' within the R3c rhombohedral average structure matrix. A careful neutron refinement suggests not only that the off-centre displacements of the cations relative to the oxygens in the R3c regions increases systematically on application of an electric field but also that the phase fraction of the IGMS regions increases systematically. The latter change in phase fraction on application of the electric field enhances the polar displacement of the cations relative to the oxygen anions and affects the overall strain response. These IGMS regions form local polar nano regions that are not correlated with one another, resulting in polarisation relaxation and strain behaviour observed in BNT-containing materials. © 2012 Elsevier Inc. All rights reserved.