共查询到20条相似文献,搜索用时 41 毫秒
1.
M. Makrenek D. Ganzke W. Haase S. Wríbel R. Dabrowski 《Molecular Crystals and Liquid Crystals》2013,570(1):573-581
Abstract New liquid crystalline substance, (S) 4-(1-methylheptyloxycarbonyl)-3-chlorophenyl 4′-(4-butanoiloxybut-1-oxy)biphenyl-4-carboxylate, exhibiting ferroelectric and antiferroelectric phases have been studied by means of frequency domain dielectric spectroscopy. DSC calorimetric and electrooptic measurements were done to study its phase transitions and electrooptic behaviour. In the antiferroelectric SmCA* phase one of the dielectric relaxation modes exhibits a non-Arrhenius behaviour. The plots of critical frequencies and dielectric increments vs. temperature show an anomalous behaviour of the relaxation processes in the neighbourhood of the ferroelectric — antiferroelectric phase transition. Reversal current method reveals one current peak in the ferroelectric phase and two in the antiferroelectric one. Temperature dependencies of tilt angle, spontaneous polarization, switching time and transmittance are also presented and discussed in scope of the mean-field theory. 相似文献
2.
E. S. Gagarina E. I. Éknadiosyants L. A. Reznichenko L. A. Shilkina I. P. Raevskii V. P. Sakhnenko V. G. Smotrakov V. V. Eremkin 《Crystallography Reports》2002,47(6):979-990
The domain structure of single-crystal and ceramic samples of Na1 ? x LixNbO3 solid solutions (at x ≤ 0.14) in the orthorhombic ferroelectric and antiferroelectric phases at room temperature is investigated by optical and electron microscopies and X-ray diffraction. The characteristic feature of the domain structure is the formation of 90° complexes consisting of laminar domains with a specific orientation relative to the lattice of the initial cubic phase. Consideration is given to the specific features in packing of these complexes and typical configurations of domains in the crystals. Observations revealed that the domain structure can involve 90°, 60°, 120°, and 180° boundaries, as well as (hhl) boundaries of the S type whose orientation depends on the cell distortion and changes with a variation in x. The indices of these boundaries are determined. The density of 180° boundaries in the ferroelectric phase is very low compared to that of non-90° boundaries. 相似文献
3.
Yumiko Takahashi Atsuo Iida Yoichi Takanishi Toyokazu Ogasawara Ken Ishikawa Hideo Takezoe 《Molecular Crystals and Liquid Crystals》2013,570(1):853-860
Abstract Direct observation of the local layer response of an antiferroelectric liquid crystal to the step form electric field has been carried out by a time resolved synchrotron X-ray micro diffraction measurement. When an electric field was changed from high voltage to OV, corresponding to the ferroelectric to antiferroelectric phase transition, the local layer transformed from the bookshelf to the quasi-bookshelf structure within 0.3 ms. The horizontal chevron structure was found in both the phases, though the decrease in the horizontal chevron angle was observed during a period of 0.2 ms after turning off the electric field. In the antiferroelectric to ferroelectric phase transition process (from OV to high voltage), the layer structure transformed to the bookshelf within 0.04 ms. 相似文献
4.
The formation of ferroelectric domains in triglycine sulfate crystal in the para–ferroelectric phase transition has been investigated in situ by piezoresponse force microscopy. The domain structure has been analyzed using the images of Fourier transforms of the scanned (010) surface of natural cleavage. The formation of a quasi-periodic one-dimensional structure of 180° domains with dominant components of one sign below T C near the transition point is revealed and crystallographic reference to the laboratory coordinate system is performed. 相似文献
5.
6.
L. A. Reznichenko L. A. Shilkina E. S. Gagarina I. P. Raevskii E. A. Dul’kin E. M. Kuznetsova V. V. Akhnazarova 《Crystallography Reports》2003,48(3):448-456
The relation between the phase transition in the vicinity of 420 K discovered earlier and the formation of an incommensurate phase in the temperature range 410–460 K is established based on the X-ray, dielectric, and dilatometric studies of sodium niobate (NaNbO3) single crystals and ceramics. It is also established that this phase is characterized by temperature and temporal instabilities. Anomalies in some physical characteristics in the vicinity of 350 K are revealed. It is also shown that the thermodynamic history of the samples is important for the coexistence of the regions of the ferroelectric Q and antiferroelectric P phases in NaNbO3. 相似文献
7.
M. F. Kupriyanov E. V. Petrovich E. V. Dutova Yu. V. Kabirov 《Crystallography Reports》2012,57(2):205-207
The temperature changes in the PbHfO3 structure in the temperature range of 20 < t < 400°C have been studied by X-ray powder diffraction. The sequence of phase changes with an increase in temperature was
found to be as follows: orthorhombic phase Pbam (O1), orthorhombic phase C2mm (O2), tetragonal phase P4mm (T), and cubic phase Pm3m (C). The C2mm and P4mm phases are ferroelectric, which is confirmed by measuring the dependences ɛ(t). The similarity of the transition pattern obtained with the known transition sequences for ferroelectric (barium titanate,
potassium niobate, and lead titanate) and antiferroelectric (lead zirconate) oxides is analyzed. 相似文献
8.
L. M. Blinov S. P. Palto V. V. Lazarev A. R. Geivandov S. G. Yudin 《Crystallography Reports》2006,51(5):843-849
An antiferroelectric liquid-crystal (LC) material formed of banana-shaped molecules in the sandwich metal-thin Langmuir-Blodgett
film-metal geometry, which is typical of solid-state technology, is investigated. Upon heating the thin-film elements, the
material passes to the high-temperature (68–127°C) LC B
2 phase, which, despite severe limitation on the film thickness (∼100 nm or less), exhibits antiferroelectric switching, which
was previously observed only in bulk samples (10 μm thick) of the LC studied. At film thicknesses smaller than ∼40 nm, ferroelectric
switching is observed, which is caused by the stabilization of the ferroelectric LC phase by the boundary surfaces. The largest
values of the switched polarization of films (∼400 nC/cm2) are comparable with the polarization of bulk samples. The coercive field increases with decreasing film thickness and reaches
∼106 V/cm for the thinnest films. This value corresponds to the intrinsic coercive field of the ferroelectric under conditions
of a strong surface effect, which suppresses domain processes.
Published in Russian in Kristallografiya, 2006, Vol. 51, No. 5, pp. 898–905.
Dedicated to the 60th Birthday of M.V. Kovalchuk
The text was submitted by the authors in English. 相似文献
9.
Yu. V. Shaldin 《Crystallography Reports》2002,47(3):484-488
The temperature dependence of spontaneous polarization in SbNbO4: Fe crystals has been studied. The temperatures of the ferroelectric and the structural phase transitions (537 ± 1) K and (876 ± 1) K are determined from the permittivity data. The anomalies in the temperature dependence of Ps provided by the presence of the FeSb and (O i V Sb)-type impurity centers are observed in the whole range of ferroelectric ordering. In the SbNbO4 structure, the macrofragments—two types of mesotetrahedra formed by Sb ions and NbO6-octahedra-are established, which are responsible for the spontaneous polarization of the crystal. 相似文献
10.
The small-angle X-ray scattering in calomel (univalent mercury chloride Hg2Cl2) single crystals at low temperatures has been investigated. Data on the size of superstructural ferroelectric domains have been obtained for the first time. Lang measurements with anomalous X-ray transmission have made it possible to trace the temperature dynamics of crystal lattice of the high-temperature D4h phase of Hg2Cl2 from 300 K to the Curie temperature (186 K) and the formation of ferroelastic domains in the temperature range of 186–100 K. The lowering of paraphase symmetry in the closest vicinity of the phase transition temperature is indicative of tricritical point transition. 相似文献
11.
Relaxor antiferroelectric (Pb,La)(Zr,Sn,Ti)O3 (PLZST) with the composition near the morphotropic phase boundary shows excellent electrical properties. However, the crystal growth of PLZST is limited by the incongruent melting of the materials. Crystal growth of PLZST was induced by a platinum wire in the flux solution with 50 wt% PbO‐PbF2‐B2O3 as a solvent. The obtained PLZST single crystals are optical transparent with light yellow color. The size of the crystals in regular rectangular shape varies from 0.5 mm to 1 mm. The PLZST single crystals exhibit tetragonal phase structure. The element contents of the crystals were measured by inductively coupled plasma atomic emission spectrometry. The results show that the composition of as‐grown crystals is a little bit deviated from the starting composition. The single crystals show two dielectric peaks at 115 °C and 182 °C, corresponding to antiferroelectric‐ferroelectric and ferroelectric‐paraelectric phase transitions. The dielectric data of as‐grown crystals indicate there is typical relaxor behavior near 182 °C. The value of relaxor factor n is 1.49642. 相似文献
12.
Neutron and high resolution X‐ray diffraction investigations on perfect single crystals of RbH2PO4 (RDP), a hydrogen bonded ferroelectric of KDP type are reported. The results of crystal structure analysis from diffraction data, below and above the paraelectric ‐ ferroelectric phase transition, support a disorder ‐ order character of [PO4H2]‐‐groups. The tetragonal symmetry of the paraelectric phase with the double well potential of the hydrogen atoms obtained by diffraction, results simply from a time‐space average of orthorhombic symmetry. According to the group ‐ subgroup relation between the tetragonal space group I42d and the orthorhombic Fdd2 a short range order of ferroelectric clusters in the tetragonal phase is observed. With decreasing temperature the ferroelectric clusters increase and the long range interaction between their local polarisation vectors leads to the formation of lamellar ferroelectric domains with alternating polarisation directions at TC = 147 K. From the high resolution X‐ray data it is concluded that below TC the ferroelastic strain in the (a,b)‐plane leads to micro‐angle grain boundaries at the domain walls. The tilt angle is enhanced by an applied electric field parallel to the ferroelectric axis. The resulting dislocations at the domain walls persist in the paraelectric phase leading to a memory effect for the arrangement of twin lamellae. With increased electric field the phase transition temperature TC is decreased. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
S. E. Kichanov D. P. Kozlenko J. W. Wasicki P. Czarnecki V. P. Glazkov W. Nawrocik B. N. Savenko C. Lathe 《Crystallography Reports》2007,52(3):447-449
The structure of deuterated pyridinium perrhenate (d5PyH)ReO4 (C5D5NHReO4) is studied by X-ray diffraction at room temperature and pressures up to 3.5 GPa and by neutron diffraction in the temperature range 10–293 K and at pressures up to 2.0 GPa. Under normal conditions, this compound belongs to the orthorhombic space group Cmc21 (ferroelectric phase II). At room temperature and pressures above P > 0.7 GPa, a transition to an orthorhombic phase (paraelectric phase II) is observed. This paraelectric phase is described by the space group Cmcm. At a pressure as high as P = 2.0 GPa, phase I remains stable at temperatures down to 10 K. This fact indicates that the high pressure suppresses the ferroelectric state in deuterated pyridinium perrhenate (d5PyH)ReO4. 相似文献
14.
Polymorphism and polar properties of an antiferroelectric (R)-2-methylheptyloxycarbonylphenyl-4-[(4-decyloxy-3-fluoro)benzoyloxy]benzoate liquid crystal are studied. The phases are identified, and the phase transition points are determined. Dielectric constant, dielectric losses, and pyroelectric properties are studied for the orthogonal smectic SmA and tilted smectic, SmC α * , SmC *, SmC γ * , and SmC A * phases. The temperature dependence of spontaneous polarization is measured by the repolarization current technique and integration of the pyroelectric constant. 相似文献
15.
Spontaneous twisting of (NH4)2SO4 crystals at the phase transition from the paraelectric phase Pnam to the ferroelectric phase Pna2 (T C = 223 K) was studied using the method of low-frequency torsion pendulum. It is shown that the macroscopic twisting of samples is caused by the rearrangement of ferroelastic twins with the {011} and {031} twinning planes existing in both the paraelectric and ferroelectric phases. A model interpreting the effect of the spontaneous twisting below the ferroelectric Curie point is proposed. 相似文献
16.
Precision X-ray structural investigation of Cd1 ? x Zn x Te single crystals (x = 0.04, 0.10, 0.21, 0.30, 0.40) is performed at temperatures below and above the ferroelectric phase transition. The regularities associated with the increase in the concentration of Zn atoms in solid solutions are revealed. It is established that the unit cell parameter of the crystals varies according to the Vegard law. The thermal parameters of Te and Zn atoms are strongly overestimated within the model of a sphalerite-type average structure. It is found that the positions of the Zn cations are split and the anion sublattice is disordered in such a way that the Te anions are predominantly displaced along the threefold axes. The Zn atoms can serve as off-center impurities. This phenomenon offers strong possibilities for manifesting the ferroelectric properties in the solid solutions under investigation. 相似文献
17.
Abstract In order to elucidate the hysteresis-free response (V-shaped response) observed at a transmittance of light in antiferroelectric smectic materials, the dynamical responses of the order parameters to an electric field are studied on the basis of an extended ANNNI model with J 3 < 0. It is shown that the V-shaped responses appear at mesophases with long period near the ferroelectric phase in low frequency range. 相似文献
18.
V. A. Isupov 《Crystallography Reports》2004,49(5):719-723
The most interesting problems in the crystal chemistry of ferroelectric and antiferroelectric perovskites PbB
0.5
′
B
0.5
″
O3 are considered. The properties and specific features of perovskites (such as the smearing of ferroelectric phase transitions,
relaxor state, ferroelectric-antiferroelectric transformations, and spontaneous phase transitions to a macrodomain state)
depend on the distribution of B′ and B″ ions over octahedral positions of the crystal lattice, i.e., on the order and disorder of these ions.
__________
Translated from Kristallografiya, Vol. 49, No. 5, 2004, pp. 806–810.
Original Russian Text Copyright ? 2004 by Isupov. 相似文献
19.
V. K. Malinovskii A. M. Pugachev H. V. Surovtsev A. P. Shebanin 《Crystallography Reports》2004,49(1):119-122
A central peak has been revealed in the Raman spectrum of ferroelectric crystals of lithium niobate LiNbO3 in the temperature range 80–300 K. It is shown that the extrapolation of the central peak, which manifests itself in inelastic-light-scattering spectra near the ferroelectric transition (Tc ~ 1400 K), cannot account for the existence of the central peak so far from the phase transition. 相似文献
20.
《Journal of Non》2007,353(47-51):4422-4427
The percolative nature of the ferroelectric phase transition in a potassium tantalate niobate (KTN) crystal is studied using time domain dielectric spectroscopy. A relaxation process linked to the off-center niobium ions is observed. The dynamic nature of this relaxation shows well defined temperature regimes in which it progresses from independent (Arrhenius) to cooperative (Vogel–Fulcher–Tammann) behavior. A recursive fractal model was applied in order to interpret the data obtained from the dielectric measurements. The structural parameters, ν and μ, derived from the correlation functions, enable the investigation of the onset of the phase transition in terms of the fractal dimensions of the polarization excitation. 相似文献