1,732 research outputs found
Dynamics of relaxor ferroelectrics
We study a dynamic model of relaxor ferroelectrics based on the spherical
random-bond---random-field model and the Langevin equations of motion. The
solution to these equations is obtained in the long-time limit where the system
reaches an equilibrium state in the presence of random local electric fields.
The complex dynamic linear and third-order nonlinear susceptibilities
and , respectively, are calculated as
functions of frequency and temperature. In analogy with the static case, the
dynamic model predicts a narrow frequency dependent peak in ,
which mimics a transition into a glass-like state.Comment: 15 pages, Revtex plus 5 eps figure
Epitaxial growth and structural characterization of Pb(Fe1/2Nb1/2)O3 thin films
We have grown lead iron niobate thin films with composition Pb(Fe1/2Nb1/2)O3
(PFN) on (0 0 1) SrTiO3 substrates by pulsed laser deposition. The influence of
the deposition conditions on the phase purity was studied. Due to similar
thermodynamic stability spaces, a pyrochlore phase often coexists with the PFN
perovskite phase. By optimizing the kinetic parameters, we succeeded in
identifying a deposition window which resulted in epitaxial perovskite-phase
PFN thin films with no identifiable trace of impurity phases appearing in the
X-ray diffractograms. PFN films having thicknesses between 20 and 200 nm were
smooth and epitaxially oriented with the substrate and as demonstrated by RHEED
streaks which were aligned with the substrate axes. X-ray diffraction showed
that the films were completely c-axis oriented and of excellent crystalline
quality with low mosaicity (X-ray rocking curve FWHM<0.09). The surface
roughness of thin films was also investigated by atomic force microscopy. The
root-mean-square roughness varies between 0.9 nm for 50-nm-thick films to 16 nm
for 100-nm-thick films. We also observe a correlation between grain size,
surface roughness and film thickness.Comment: 13 Pages, 6 figures. To be published in J. Mag. Mag Mater.
proceedings of EMRS200
Size effects in the thin films of order - disorder ferroelectrics subject to the depolarization field
The films of order-disorder type ferroelectrics were considered in the mean
field approximation taking into account depolarization field. It was shown that
size effects in this system could be described on the base of bulk system
equation of state with Curie temperature dependent on the film thickness. The
critical size hc and critical temperature Tc of phase transition from
ferroelectric to paraelectric phase was calculated allowing for the
depolarization field contribution. The comparison of the polarization
dependence on the film thickness, temperature and electric field for the films
of order-disorder and displacement type ferroelectrics is performed. In
particular it was shown that all the dipoles become ordered at T=0
independently on the film thickness for h>hc contrary to the displacement type
ferroelectrics. Critical thickness appeared larger and polarization
distribution sharper for the displacement type ferroelectrics than for
order-disorder type ferroelectrics.Comment: 7 pages, 4 figures, 1 tabl
The Soft Mode in H-Bonded Ferroelectrics Revisited
The nature of the soft tunneling modes in KH2P04 type
ferroelectrics is discussed and a new model is described for the
proton-lattice coupling in these systems
THERAPY AND QUALITY OF LIFE OF PATIENTS WITH PSYCHOSIS
The symptoms and the individual experience of psychosis vary from patient to patient. Treatment, medication and cognitive psychotherapy are targeted mostly on positive and lately also on negative symptoms of psychosis. Deficits in metacognition found in patients with psychosis have a profound impact on the recovery process, their quality of life and experience of mental pain. Long term group psychotherapy helps patients to mourn their loss, improve their metacognition, and reduce the stigma and mental pain in patients with psychosis
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