Browsing by Subject "batio3"

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Crystallographic Changes In Lead Zirconate Titanate Due To Neutron Irradiation
(2014-11) Henriques, A.; Graham, J. T.; Landsberger, S.; Ihlefeld, J. F.; Brennecka, G. L.; Brown, D. W.; Forrester, J. S.; Jones, J. L.; Landsberger, Sheldon
Piezoelectric and ferroelectric materials are useful as the active element in non-destructive monitoring devices for high-radiation areas. Here, crystallographic structural refinement (i. e., the Rietveld method) is used to quantify the type and extent of structural changes in PbZr0.5Ti0.5O3 after exposure to a 1 MeV equivalent neutron fluence of 1.7x10(15) neutrons/cm(2). The results showa measurable decrease in the occupancy of Pb and O due to irradiation, with O vacancies in the tetragonal phase being created preferentially on one of the two O sites. The results demonstrate a method by which the effects of radiation on crystallographic structure may be investigated. (C) 2014 Author(s).
Pseudo Jahn-Teller Effect In The Origin Of Enhanced Flexoelectricity
(2015-01) Bersuker, Issac B.; Bersuker, Issac B.
The controversy between the theory and experiment in explaining the origin of enhanced flexoelectricity is removed by taking into account the pseudo Jahn-Teller effect (PJTE) which, under certain conditions, creates local dipolar distortions of dynamic nature, resonating between two or more equivalent orientations. The latter become nonequivalent under a strain gradient thus producing enhanced flexoelectricity: it is much easier to orient ready-made dipoles than to polarize an ionic solid. For BaTiO3, the obtained earlier numerical data for the adiabatic potential energy surface in the space of dipolar displacements in the Ti centers were used to estimate the flexoelectric coefficient integral in the paraelectric phase in a one-dimensional model with the strain gradient along the [111] direction: integral = -0.43 X 10(-6) Cm-1. This eliminates the huge contradiction between the experimental data of integral similar to mu Cm-1 for this case and the theoretical predictions (without the PJTE) of 3-4 orders-of-magnitude smaller values. Enhanced flexoelectricity is thus expected in solids with a sufficient density of centers that have PJTE induced dipolar instabilities. It explains also the origin of enhanced flexoelectricity observed in other solids, noticeable containing Nb perovskite centers which are known to have a PJTE instability, similar to that of Ti centers. The SrTiO3 crystal as a virtual ferroelectric in which the strain gradient eases the condition of PJTE polar instability is also discussed. (C) 2015 AIP Publishing LLC.