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1.
Lagerwall JP Heppke G Giesselmann F 《The European physical journal. E, Soft matter》2005,18(1):113-121
We study the effects of mixing ferroelectric and antiferroelectric liquid-crystal compounds (FLCs and AFLCs) when the former
are strictly synclinic and the latter strictly anticlinic, i.e. one mixture component exhibits only SmC* and the other only SmC a* as tilted phase. Three different paths between syn- and anticlinicity were detected: transition directly between SmC* and
SmC a*, transition via the SmCβ* and SmCγ* subphases, or by “escaping” the clinicity frustration by reducing the tilt to zero, i.e. the SmA* phase is extended downwards in temperature, separating SmC* from SmC a* in the phase diagram. The most common path is the one via the subphases, demonstrating that these phases appear as a result
of frustration between syn- and anticlinic and, consequently, between syn- and antipolar order. For assessing the role of
chirality, we also replaced the FLC with non-chiral synclinics. With one of the AFLCs, the route via supbhases was detected
even in this case, suggesting that chirality --although necessary-- does not have quite the importance that has previously
been attributed to the appearance of the subphases. The path chosen in the mixture study seemed to be determined mainly by
the synclinic component, the subphase induction occurring only when the SmA*-SmC* transition was second order. 相似文献
2.
Ch. Schwan F. Martin G. Jakob J.C. Martinez H. Adrian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):477-481
We have investigated the crystal structure and the ferroelectric properties of BaTiO3 thin films with YBa2Cu3O as the bottom and Au as the top electrode. Epitaxial heterostructures of YBa2Cu3O and BaTiO3 were prepared by dc and rf sputtering, respectively. The crystal structure of the films was characterised by X-ray diffraction.
The ferroelectric behaviour of the BaTiO3 films was confirmed by hysteresis loop measurements using a Sawyer Tower circuit. We obtain a coercive field of 30 kV/cm
and a remanent polarisation of 1.25 μC/cm2. At sub-switching fields the capacitance of the films obeys a relation analogous to the Rayleigh law. This behaviour indicates
an interaction of domain walls with randomly distributed pinning centres. At a field of 5 MV/m we calculate a 3% contribution
of the irreversible domain wall motion to the total dielectric constant.
Received 24 June 1999 and Received in final form 27 August 1999 相似文献
3.
Summary We present second harmonic generation results which, for the first time, allow us to assess the correlation length of the
order parameter exhibited by the mixed crystal K1−x
Na
x
TaO3. Our data, including linear birefringence results, evidence a transition to a polar state characterized, for a 15% Na doped
sample, by clusters of size 0.12 to over 1 μm and a spontaneous polarization of 503 mC/m2. Even if these findings can be consistent with a ferroelectric transition characterized by long-range order, precursor effects
and the behaviour of hysteresis are more indicative of a glass-type transition. 相似文献
4.
P. Khare D. Sa 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):205-209
Using a phenomenological Landau theory, the size dependence on ferroelectric
transition for free-standing long cylindrical nanoparticles is discussed.
We derive
the size dependence of the transition temperature, polarization profile as
well as the static susceptibility. The transition temperature vanishes below
a critical size where the static susceptibility shows divergence obeying
Curie-Weiss law. In order to make this result compared with experiments,
the average polarization and the susceptibility is computed with a Gaussian
particle size distribution. The average polarization in such a case shows
smearing with respect to the particle size whereas the divergence in the
susceptibilty gets rounded. This might correspond to a size dependent soft
mode which can be observed in Raman measurement. 相似文献
5.
R. Enjalbert J. Galy Y. Vysochanskii A. Ouédraogo P. Saint-Grégoire 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):169-177
The structural change occurring in between the paraelectric and the ferroelectric phases is investigated by means of X-ray diffraction. Details of the structure
in both phases are obtained and the role of the lone pair is discussed in the light of structural data. In agreement with the 2/
m to m symmetry lowering, polar displacements are found within the m plane away from a particular crystallographic direction but antiparallel displacements occur also. These results are discussed
in the frame of the phenomenological theory which predicts a particular temperature dependence of the dielectric polarization
in this crystal.
Received: 10 July 1998 相似文献
6.
L. Zhang W. L. Zhong C. L. Wang Y. P. Peng Y. G. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):565-573
The size effect of the dielectric properties and the barrier height was investigated in the ferroelectric solid solution BaxSr1-xTiO3 system. The decrease of the grain size causes the suppression of the ferroelectricity, and the increase of the relaxation
frequency. Barrier heights increase with increasing grain size. The result is analogous to magnetic phase transitions in nanocrystals
and other solid-solid phase transitions in nanocrystals. It suggests a general rule that may be of use in the discovery of
new metastable phases. An explanation of this phenomenon was given by an electric potential model that agrees well with the
experimental results. For BaxSr1-xTiO3 system, the decrease of xcauses the decrease of the barrier height.
Received 3 August 1998 and Received in final form 22 November 1998 相似文献
7.
J. Dec W. Kleemann Th. Woike R. Pankrath 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):627-632
The complex dielectric susceptibility of Sr
0.61
Ba
0.39
Nb
2
O
6
:Ce
3+
(SBN61:Ce) has been measured at frequencies and temperatures before and after poling. The relaxor behaviour with large polydispersivity observed above the ferroelectric phase transition
temperature, T
c
= 360 and 340 K for x
(Ce) = 0 and 0.0066, respectively, is perfectly modeled within the framework of Chamberlin's dynamically correlated domain approach.
Below T
c
the dynamic nanodomain state crosses over into a ferroelectric state with polydispersive domain wall dynamics at very low
frequencies. Presumably SBN61:Ce belongs to the three-dimensional random field Ising rather than to the dipole glass universality
class.
Received 1 October 1999 相似文献
8.
A. Bussmann-Holder A. R. Bishop 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(3):279-282
Motivated by recent experiments demonstrating suppression of
ferroelectricity with pressure in SrTi18O3, the dynamics of the
phase transition mechanism are reinvestigated within a nonlinear
polarizability model. For temperatures far above the phase transition polar
micro domains are formed which increase in size with decreasing temperature
to freeze out at Tc without forming long range order. Experimentally,
soft mode dynamics are simultaneously observed, evidencing that displacive
and order/disorder features coexist. In the ferroelectric phase both
components persist whereby an incomplete and inhomogeneous ferroelectric
state is formed. 相似文献
9.
B. Fugiel 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):159-163
The parameters of the hysteresis loop in the ferroelectric Rochelle salt
were investigated using a sample with two pairs of electrodes: measurement
electrodes and the side ones. It has been shown that the difference between
the potentials of the measurement and the side electrodes (generating an
inhomogeneous electric field) leads to gradual decay in time t of the
remanent polarization Pr. The time required for the hysteresis loop to
disappear in the inhomogeneous electric field (not parallel to the
ferroelectric axis) decreases with temperature increase from 44±3 h
at – 9°C to 2.3±0.1 h at 21.9 °C. On the other hand, the
crystal placed for a sufficiently long time simultaneously in the measuring
electric field and in the constant inhomogeneous one may finally exhibit a
stationary hysteresis loop with a reduced remanent polarization and the
unchanged coercive field. It has been shown that the crystal as a whole does
not have to be polarized perpendicularly to the ferroelectric axis in order
for its hysteresis loop to be reduced. 相似文献
10.
A Copper–Formate Framework Showing a Simple to Helical Antiferroelectric Transition with Prominent Dielectric Anomalies and Anisotropic Thermal Expansion,and Antiferromagnetism
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Ran Shang Sa Chen Prof. Zhe‐Ming Wang Prof. Song Gao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(48):15872-15883
We present here the compound [NH4][Cu(HCOO)3], a new member of the [NH4][M(HCOO)3] family. The Jahn–Teller Cu2+ ion leads to a distorted 49?66 chiral Cu–formate framework. In the low‐temperature (LT) orthorhombic phase, the Cu2+ is in an elongated octahedron, and the ${{\rm NH}{{+\hfill \atop 4\hfill}}}$ ions in the framework channel are off the channel axis. From 94 to 350 K the ${{\rm NH}{{+\hfill \atop 4\hfill}}}$ ion gradually approaches the channel axis and the related modulation of the framework and the hydrogen‐bond system occurs. The LT phase is simple antiferroelectric (AFE). The material becomes hexagonal above 355 K. In the high‐temperature (HT) phase, the Cu2+ octahedron is compressed, and the ${{\rm NH}{{+\hfill \atop 4\hfill}}}$ ions are arranged helically along the channel axis. Therefore, the phase transition is one from LT simple AFE to HT helical AFE. The temperature‐dependent structure evolution is accompanied by significant thermal and dielectric anomalies and anisotropic thermal expansion, due to the different status of the ${{\rm NH}{{+\hfill \atop 4\hfill}}}$ ions and the framework modulations, and the structure–property relationship was established based on the extensive variable‐temperature single‐crystal structures. The material showed long range ordering of antiferromagnetism (AFM), with low dimensional character and a Néel temperature of 2.9 K. Therefore, within the material AFE and AFM orderings coexist in the low‐temperature region. 相似文献