Antiferroelectric Type Research Articles

Arctic curves of the four-vertex model

We consider the four-vertex model with a special choice of fixed boundary conditions giving rise to limit shape phenomena. More generally, the considered boundary conditions relate vertex models to scalar products of off-shell Bethe states, boxed plane partitions, and fishnet diagrams in quantum field theory. In the scaling limit, the model exhibits the emergence of an arctic curve separating a central disordered region from six frozen ‘corners’ of ferroelectric or anti-ferroelectric type. We determine the analytic expression of the interface by means of the Tangent Method. We supplement this heuristic method with an alternative, rigorous derivation of the arctic curve. This is based on the exact evaluation of suitable correlation functions, devised to detect spatial transition from order to disorder, in terms of the partition function of some discrete log-gas associated to the orthogonalizing measure of the Hahn polynomials. As a by-product, we also deduce that the arctic curve’s fluctuations are governed by the Tracy–Widom distribution.

Structural Features of Phosphates Ca9 – xMxDy(PO4)7 (M = Zn2+ or Mg2+)

Phosphate solid solutions based on the whitlockite family Ca9 – xMxDy(PO4)7 (M = Zn2+ or Mg2+) have been obtained. The samples have been investigated by a combination of the methods, such as X‑ray diffraction analysis, second optical harmonic generation, and luminescence spectroscopy. It is established that the unit-cell symmetry change (R3c → $$R\bar {3}c$$) in the solid-solution series with an increase in the degree of substitution Ca2+ → M2+; the concentration dependence is determined. Phase transitions of the ferro- and antiferroelectric types, as well as their temperature positions, have been determined by dielectric spectroscopy. The synthesized samples exhibit strong luminescence under 350-nm excitation with the resulting radiation in the white region in color coordinates.

Структурные особенности фосфатов Ca-=SUB=-9-x-=/SUB=-M-=SUB=-x-=/SUB=-Dy(PO-=SUB=-4-=/SUB=-)-=SUB=-7-=/SUB=- (M=Zn-=SUP=-2+-=/SUP=-, Mg-=SUP=-2+-=/SUP=-)

Solid solutions of phosphate with whitlockite-type Ca9-xMxDy (PO4) 7 (M = Zn2 +, Mg2 +) were obtained. The samples were studied by a complex of methods, such as X-ray phase analysis, second harmonic generation, and luminescent spectroscopy. It was established that in the series of solid solutions a change in the symmetry of the unit cell R3c-> R 3c is observed during Ca2+ -M2+ substitution, and the concentration dependence was determined. The phase transitions of the ferroelectric and antiferroelectric type and their temperature position were established by dielectric spectroscopy. The synthesized samples demonstrate intense luminescence with 350 nm excitation and the resulting radiation is in the white region of color coordinates (CIE).

Study of ferro- and anti-ferroelectric polar order in mesophases exhibited by bent-core mesogens

Ferroelectric nature in the NCybC phase and anti-ferroelectric nature in the SmC(I) and SmC(II) phases.

Piezoelectric and functional properties of materials with coexisting ferroelectric and antiferroelectric phases

A brief review of investigations of lead zirconate-titanate based solid solutions with coexisting ferroelectric and antiferroelectric types of dipole ordering is presented. Our goal is to demonstrate the importance of the inhomogeneous state of domain of these phases in formation of properties of these substances, in the search for new piezoelectric ceramic materials, as well as development of new functional materials. An analysis of physical phenomena and peculiarities of behavior of these materials caused by the presence of domains of the coexisting ferroelectric and antiferroelectric phases is presented. Several specific effects caused by this coexistence of phases which are important and significant for applications of these materials in devices are discussed.

Core-to-core dimers forming switchable mesophase.

We report structurally new type of dimers composed of bent-core molecules connected through their central cores by an alkylene spacer. Various self-assembling structures are discovered when prolonging the terminal alkyl chains in arms. Among diverse mesophases, the antiferroelectric type of switching under an applied electric field is observed.

Structure formation in monolayers composed of hard bent-core molecules

ABSTRACTWe investigate the role of excluded volume interactions instabilising different structures in monolayers filled with bent-shaped molecules using the Onsager type of density functional theory supplemented by constant-pressure Monte-Carlo simulations. We study influence of molecular features, like the apex angle, thickness of the arm and the type of the arm edges on the stability of layered structures. For simple molecular shapes taken the observed phases are dominated by the lamellar antiferroelectric type as observed experimentally, but a considerable sensitivity of the ordering to details of the molecular shape is found for order parameters and wave vectors of the structures. Interestingly, for large opening angles and not too thick molecules, a window of stable nematic splay-bend phase is shown to exist.

Magnetic and dielectric properties of Mn 2 V 2 O 7

The magnetic and dielectric properties of the manganese di-vanadate compound Mn2V2O7 are reported. The sample shows martensitic type structural transition close to room temperature which is evident both in the magnetic and dielectric data. Mn2V2O7 shows signature of antiferromagnetic type ordering around 17 K with concomitant anomaly in the dielectric properties at the same point, although no spontaneous electric polarization was found below 17 K. This clearly signifies a magnetic order driven electric anomaly and possibly it is antiferroelectric type with no net polarization. The dielectric relaxation behaviours show marked difference across the structural transition close to room temperature. Interestingly, the sample shows reversible switching behaviour across the structural transition close to 300 K between high and low dielectric states which can have important practical applications.

ChemInform Abstract: Magnetic and Magnetoelectric Properties of Rare Earth Molybdates

AbstractReview: 68 refs.

Magnetic and Magnetoelectric Properties of Rare Earth Molybdates

We present results on ferroelectric, magnetic, magneto-optical properties and magnetoelectric effect of rare earth molybdates (gadolinium molybdate, GMO, and terbium molybdate, TMO, and samarium molybdate, SMO), belonging to a new type of ferroelectrics predicted by Levanyuk and Sannikov. While cooling the tetragonal β-phase becomes unstable with respect to two degenerate modes of lattice vibrations. The β-β′ transition is induced by this instability. The spontaneous polarization appears as a by-product of the lattice transformation. The electric order in TMO is of antiferroelectric type. Ferroelectric and ferroelastic GMO and TMO at room temperature are paramagnets. At low temperatures GMO and TMO are antiferromagnetic with the Neel temperatures TN=0.3 K (GMO) and TN=0.45 K (TMO). TMO shows the spontaneous destruction at 40 kOe magnetic field. Temperature and field dependences of the magnetization in TMO are well described by the magnetism theory of singlets at 4.2 K ≤ T ≤ 30 K. The magnetoelectric effect in SMO, GMO and TMO, the anisotropy of magnetoelectric effect in TMO at T = (1.8–4.2) K, the Zeeman effect in TMO, the inversion of the electric polarization induced by the laser beam are discussed. The correlation between the magnetic moment of rare earth ion and the magnetoelectric effect value is predicted. The giant fluctuations of the acoustic resonance peak intensity near the Curie point are observed.

Phase separation in lithium intercalated anatase: A theory

Lithium intercalated anatase used in Li-ion batteries has some special features: coexistence of Li-rich and Lipoor phases as well as two possible positions for Li ions in the oxygen tetrahedron. A theoretical description of the compound considering those peculiarities is presented. As shown by the performed symmetry analysis, the intercalation induced lattice deformation can be accompanied by the ordering of antiferroelectric type (internal piezoeffect). In the following step, a qualitative illustration of the phase separation in the lithiated anatase is given within the Landau expansion at the proper choice of coefcients . A microscopic model for description of the compound is also proposed which combines features of the Mitsui and Blume-Emery-Grifts models and utilizes the symmetry analysis results. Various ground state and temperature-dependent phase diagrams of the model are studied to nd a set of model parameters corresponding to the lithiated anatase. A phase separation into the empty and half-lled phases in a wide temperature range has been found closely resembling the phase coexistence in the intercalated crystal. In the framework of the model, the two-position Li subsystem could have the ordering of ferro- or antiferroelectric types which, however, has not been yet observed by the experiment.

X‐ray diffraction and optical birefringence studies on four nematogenic difluorobenzene derivatives

The results of optical microscopy, DSC, X‐ray diffraction and optical birefringence studies on four nematogenic difluorobenzene derivatives are presented. The thermal stability of the compounds increases substantially as greater flexibility is introduced into the core structure. Average intermolecular distances, obtained from X‐ray data, are found to increase when a comparatively rigid planar phenyl ring is substituted by a flexible non‐planar cyclohexyl ring in the core structure. From the values of apparent molecular lengths in the nematic phase, a short range antiferroelectric type of association is found to exist between neighbouring molecules. Density values suggest that the molecular packing is less efficient with increasing flexibility either in chain‐ or in core‐structure. All the refractive indices exhibit normal dispersive behaviour, and a positive optical anisotropy is observed in all the compounds which decreases quickly with temperature. Temperature dependences of orientational order parameters, determined from both X‐ray and optical birefringence studies, are presented. Variations of different physical properties with order parameters are discussed.

Dielectric study of nematic and induced smectic-A phases in binary mixtures of pentyloxy cynobiphenyl with three p-azoxybenzenes

Static dielectric properties of 18 binary mixtures of 4,4′-pentyloxy cyanobiphenyl (5OCB) with 4,4′-bis(alkoxy)azoxybenzenes (nOAB) for n = 5, 6 and 7 have been studied in detail. Seventeen mixtures show induced smectic-A (SmA) phase; a few mixtures exhibit nematic phase as well. Pure 5OCB has a large positive dielectric anisotropy while nOAB members have small but negative anisotropy. However, all the mixtures exhibit positive anisotropy. In the mixtures, except those with x 5OCB ≥ 0.85, the values of ε∥, ε⊥ and increase smoothly with temperature. The values of εiso are found to be higher than the values within the mesophases, with a jump at T NI or T SI. Effective values of the dipole moments in the mixtures are found to be less than the values observed in the pure compounds. This suggests that anti-parallel homo-dimers of 5OCB exist in the mixtures as observed in the pure compound. Moreover, at the onset of SmA phase, values of are found to decrease from those in the nematic phase. This implies that additional anti-ferroelectric type of ordering is developed in the induced SmA phase. In all the mixtures the anisotropy parameter Δε decreases with concentration, becomes minimum at x 5OCB = 0.5, and then increases quite fast. Kirkwood correlation factors have also been calculated to find the nature and extent of the molecular associations.

On the Phase Transitions in Ferroelectric-Antiferroelectric Mixed Systems

A new theoretical approach to the investigation of phase transitions in ferroelectric-antiferroelectric mixed systems is proposed. The model Hamiltonian describes both long and short range interactions between particles the total dipole momentum of which can be oriented only along the z-axis (ferroelectric type of ordering), or along the x-axis (antiferroelectric type of ordering). Using the replica method for calculation of partition function for randomly distributed sites with ferroelectrically and antiferroelectrically ordering particles, the complete analysis of possible phase transitions is performed. The problem of coexistence of para-, ferro-, antiferroelectric, spin-glass and mixed phases are discussed in detail.

Dielectric constant of a highly polarizable atomic fluid: the clausius–mossotti versus the onsager relation

The relation between the dielectric constant and the particle polarizability for a polarizable liquid composed of Lennard-Jones particles carrying a saturable induced dipole is studied by computer simulations. It is shown that the widely accepted Clausius–Mossotti relation is only valid for low polarizabilities and fails for high polarizabilities. The results can be fitted accurately by an Onsager-like relation using an effective particle radius measured in the simulations which is larger than the equivalent hard-sphere radius defined conventionally. Furthermore, the orientational ordering transition found at high polarizabilities is shown to be of anti-ferroelectric type.

A Neutron Diffraction Study of Magnetically Ordered Ferroelectric Materials

Structural, magnetic, dielectric properties and Mossbauer effect were investigated on complex perovskite with composition AFe2/3B1/3O3 (A=Ca,Sr,Pb,Ba; B=W,Te). The most striking feature of this type of complex perovskites is the coexistence of magnetic and antiferroelectric types of ordering in a certain temperature interval. It was found that ferrimagnetic Ca and Sr compounds belong to a partially ordered perovskite structure, and antiferromagnetic Pb phase to a disordered one. The possible models for nuclear and magnetic structures were proposed in accordance with the observed dielectric and magnetic properties.

A Neutron Diffraction Study of Magnetically Ordered Ferroelectric Materials

A number of compounds with perovskite-type structure A(Fe0.67 B0.33)O3 (A = Ba, Pb, Sr, Ca; B = W, Te) were investigated using X-ray and neutron powder diffraction, dielectric and magnetic measurements and Mössbauer effect. The most striking feature of this type of complex perovskites is the coexistence of magnetic and antiferroelectric types of ordering in a certain temperature range. It was found that ferrimagnetic Ca, Sr and Ba compositions belong to a partially ordered perovskite-related structure, and an antiferromagnetic Pb phase to a disordered one. The possible models for nuclear and magnetic structures were proposed in accordance with the observed dielectric and magnetic properties.

X-Ray and Dielectric Studies of Fe and Nb-Substituted Pb(Mg 1/2 W 1/2 )O 3 Ceramics

The crystal structure and dielectric properties of (1 m x )Pb(Mg 1/2 W 1/2 )O 3 m x Pb(Fe 1/2 Nb 1/2 )O 3 (PMW 1 m x PFN x ) (0 h x h 0.3) solid solution have been studied by X-Ray diffraction and dielectric property measurements. On increasing PFN substitutions up to x = 0.14, the crystal structure changes from the cubic to the orthothombic at a sharp phase transition of the paraelectric(PE)-antiferroelectric(AFE) type that is independent of applied frequency. However, on further increasing PFN substitution(0.16 h x h 0.30), the dielectric constant curve as a function of temperature becomes gradually broader and the apparent transition becomes frequency-dependent while the crystal structure changes to the pseudocubic.

X-Ray and Dielectric Studies of Fe and Nb-Substituted Pb(Mg 1/2 W 1/2 )O 3 Ceramics

The crystal structure and dielectric properties of (1 m x )Pb(Mg 1/2 W 1/2 )O 3 m x Pb(Fe 1/2 Nb 1/2 )O 3 (PMW 1 m x PFN x ) (0 h x h 0.3) solid solution have been studied by X-Ray diffraction and dielectric property measurements. On increasing PFN substitutions up to x = 0.14, the crystal structure changes from the cubic to the orthothombic at a sharp phase transition of the paraelectric(PE)-antiferroelectric(AFE) type that is independent of applied frequency. However, on further increasing PFN substitution(0.16 h x h 0.30), the dielectric constant curve as a function of temperature becomes gradually broader and the apparent transition becomes frequency-dependent while the crystal structure changes to the pseudocubic.

Evolution of the atomic and magnetic structure of Sr 3Fe 2WO 9: A temperature dependent neutron powder diffraction study

Both the nuclear and magnetic structure of a complex perovskite with composition Sr 3Fe 2WO 9 (SFWO) has been studied by neutron powder diffraction (NPD) at different temperatures. The most striking feature of this type of complex perovskite is the coexistence of ferrimagnetic and antiferroelectric types of ordering below T = 373 K. The NPD data at 10 and 300 K were refined with a model in the tetragonal space group I4/m. SFWO has a partially ordered perovskite structure, in which Fe and W cations distribute regularly to some degree at the B-sites in the ABO 3 perovskite lattice. For both temperatures magnetic diffraction peaks were registered, and a possible model for the magnetic structure was proposed in accordance with the ferrimagnetic properties of SFWO.