Ferrielectric Phase Research Articles

Composition-driven structural variation in ferrielectric phase of (Bi1/2Na1/2)TiO3-Ba(Mg1/3Nb2/3)O3

We investigate the structural variation in the ferrielectric P4bm phase of (1−x)(Bi1/2Na1/2)TiO3–xBa(Mg1/3Nb2/3)O3 (BNT–BMN) by using high-resolution neutron powder diffraction (NPD) analysis. The NPD study on single-phase BNT–BMN powders obtained by a two-step calcination process reveals that a boundary between rhombohedral R3c and tetragonal P4bm phases exists at x = 4%. The Rietveld analysis reveals that the P4bm phase (x = 5%–10%) exhibits an isotropic expansion of the crystal lattice as well as a decrease in rotation angle of the oxygen octahedra when the BMN composition (x) increases. The compositional-driven variation in the P4bm structure strongly suggests that the polarization and octahedral rotation behaviors associated with phase transition, which is called polarization twist, has a crucial role in the enhancement of polarization properties of BNT–BMN.

Chiral Incommensurate Helical Phase in a Smectic of Achiral Bent-Core Mesogens.

An achiral, bent-core mesogen forms several tilted smectic liquid crystal phases, including a nonpolar, achiral de Vries smectic A which transitions to a chiral, ferroelectric state in applied electric fields above a threshold. At lower temperature, a chiral, ferrielectric phase with a periodic, supermolecular modulation of the tilt azimuth, indicated by a Bragg peak in carbon-edge resonant soft x-ray scattering, is observed. The absence of a corresponding resonant umklapp peak identifies the superlayer structure as a twist-bend-like helix that is only weakly modulated by the smectic layering.

Layered ferrielectric crystals CuInP2S(Se)6: a study from the first principles

ABSTRACTLayered CuInPS(Se) crystals in ferrielectric and paraelectric phases were investigated for the first time via the plane-wave pseudo-potential methodology within density functional theory (DFT). Was proved that structural and electronic properties of the van der Waals layered crystals should be calculated applying dispersion correction to the DFT formalism. The partial and projected density of states were used to evaluate the electronic band structure changes under phase transition. Instability of the CuInPS(Se) crystals was successfully explained by the second-order Jahn-Teller effect.

Symmetry-determined antiferroelectricity in PbZrO3 , NaNbO3 , and PbHfO3

Like ferroelectric or ferroelastic phase transitions, antiferroelectric transitions can be predicted by symmetry. This property is illustrated by a theoretical analysis of the complex phase transitions, occurring in the perovskite compounds $\mathrm{PbZr}{\mathrm{O}}_{3}$, $\mathrm{NaNb}{\mathrm{O}}_{3}$, and $\mathrm{PbHf}{\mathrm{O}}_{3}$, which involve the coupling of several order parameters. The symmetry-breaking order parameters associated with the transitions in the three compounds are determined. The antiferroelectric transitions are shown to verify specific symmetry criteria, which consist of the emergence at the local scale of polar site symmetries coinciding with symmorphic subgroups of the antiferroelectric space group. The theoretical temperature--electric-field phase diagram of $\mathrm{PbZr}{\mathrm{O}}_{3}$ involving ferrielectric and ferroelectric phases is worked out.

Resonant x-ray scattering observation of transitional subphases during the electric-field-induced phase transition in a mixture of Se-containing chiral smectic liquid crystals.

Using resonant x-ray scattering techniques, transitional subphases during the electric-field-induced phase transition of a mixture of Se-containing chiral liquid crystals, 80% AS657 and 20% AS620, in a planar-aligned cell geometry were investigated, where the prototypical phase sequence SmC_{A}^{*}-SmC_{γ}^{*}-AF-SmC^{*} was observed; the transitional subphases were formed during the transition from the three-layer periodicity phase to the ferroelectric phase. In the lower-temperature range where the three-layer SmCγ^{*} phase appeared under the low electric field, nine- and six-layer subphases and a "streak" pattern appeared in sequence after the transition from the SmCγ^{*} phase with increasing applied electric field; the ferroelectric phase was realized. In the higher-temperature range where the four-layer AF phase appeared under a low electric field, the AF phase changed to a three-layer phase at the medium electric field. The twelve-, nine-, and six-layer subphases subsequently appeared in sequence, and finally the ferroelectric phase was generated with increasing electric field. The molecular arrangements of the field-induced subphases, especially the newly found nine-layer periodicity phase, was analyzed. The successive field-induced phase transition of the present results was compared with that of our previous results for pure Se-containing and Br-containing liquid crystals, and the relation to the three-layer ferrielectric phase was discussed.

Antiferroelectric‐ferroelectric phase transition in lead‐free AgNbO3 ceramics for energy storage applications

AbstractThe high‐energy storage density reported in lead‐free AgNbO3 ceramics makes it a fascinating material for energy storage applications. The phase transition process of AgNbO3 ceramics plays an important role in its properties and dominates the temperature and electric field dependent behavior. In this work, the phase transition behavior of AgNbO3 ceramics was investigated by polarization hysteresis and dielectric tunability measurements. It is revealed that the ferrielectric (FIE) phase at room temperature possesses both ferroelectric (FE)‐like and antiferroelectric (AFE)‐like dielectric responses prior to the critical AFE‐FE transition point. A recoverable energy storage density of 2 J/cm3 was achieved at 150 kV/cm due to the AFE‐FE transition. Based on a modified Laudau phenomenological theory, the stabilities among the AFE, FE and FIE phases are discussed, laying a foundation for further optimization of the dielectric properties of AgNbO3.

Comments on the published article “Electric field induced transformations and dielectric properties of ferrielectric smectic phase” by T. Soltani et al., Journal of Molecular Liquids, 199 (2014) 162–166

This Letter concerns errors and shortcomings in the article by T. Soltani et al., “Electric field induced transformations and dielectric properties of ferrielectric smectic phase”, Journal of Molecular Liquids, 199 (2014) 162–166.

Cation-Eutectic Transition via Sublattice Melting in CuInP2S6/In4/3P2S6 van der Waals Layered Crystals.

Single crystals of the van der Waals layered ferrielectric material CuInP2S6 spontaneously phase separate when synthesized with Cu deficiency. Here we identify a route to form and tune intralayer heterostructures between the corresponding ferrielectric (CuInP2S6) and paraelectric (In4/3P2S6) phases through control of chemical phase separation. We conclusively demonstrate that Cu-deficient Cu1-xIn1+x/3P2S6 forms a single phase at high temperature. We also identify the mechanism by which the phase separation proceeds upon cooling. Above 500 K both Cu+ and In3+ become mobile, while P2S64- anions maintain their structure. We therefore propose that this transition can be understood as eutectic melting on the cation sublattice. Such a model suggests that the transition temperature for the melting process is relatively low because it requires only a partial reorganization of the crystal lattice. As a result, varying the cooling rate through the phase transition controls the lateral extent of chemical domains over several decades in size. At the fastest cooling rate, the dimensional confinement of the ferrielectric CuInP2S6 phase to nanoscale dimensions suppresses ferrielectric ordering due to the intrinsic ferroelectric size effect. Intralayer heterostructures can be formed, destroyed, and re-formed by thermal cycling, thus enabling the possibility of finely tuned ferroic structures that can potentially be optimized for specific device architectures.

Polar Nature of (CH3NH3)3Bi2I9 Perovskite-Like Hybrids.

High-quality single crystals of perovskite-like (CH3NH3)3Bi2I9 hybrids have been synthesized, using a layered-solution crystal-growth technique. The large dielectric constant is strongly affected by the polar ordering of its constituents. Progressive dipolar ordering of the methylammonium cation upon cooling below 300 K gradually converts the hexagonal structure (space group P63/mmc) into a monoclinic phase (C2/c) at 160 K. A well-pronounced, ferrielectric phase transition at 143 K is governed by in-plane ordering of the bismuth lone pair that breaks inversion symmetry and results in a polar phase (space group P21). The dielectric constant is markedly higher in the C2/c phase above this transition. Here, the bismuth lone pair is disordered in-plane, allowing the polarizability to be substantially enhanced. Density functional theory calculations estimate a large ferroelectric polarization of 7.94 μC/cm2 along the polar axis in the P21 phase. The calculated polarization has almost equal contributions of the methylammonium and Bi3+ lone pair, which are fairly decoupled.

Theory of antiferroelectric phase transitions

At variance with structural ferroic phase transitions which give rise to macroscopic tensors coupled to macroscopic fields, criteria defining antiferroelectric (AFE) phase transitions are still under discussion due to the absence of specific symmetry properties characterizing their existence. They are recognized by the proximity of a ferroelectric (FE) phase induced under applied electric field, with a double hysteresis loop relating the induced polarization to the electric field and a typical anomaly of the dielectric permittivity. Here, we show that there exist indeed symmetry criteria defining AFE transitions. They relate the local symmetry of the polar crystallographic sites emerging at an AFE phase transition with the macroscopic symmetry of the AFE phase. The dielectric properties of AFE transitions are deduced from a Landau theoretical model in which ferroelectric and ferrielectric phases are shown to stabilize as the result of specific symmetry-allowed couplings of the AFE order- parameter with the field-induced polarization.

Effects of interaction in the Hofstadter regime of the honeycomb lattice

We investigate phases of spinless fermions on the honeycomb lattice with nearest neighbor interaction in the Hofstadter regime. The interaction induces incompressible nematic and ferri-electric phases with broken translation symmetry. Some of the transitions are accompanied by changes in the Hall conductivity. We study pair correlations and show that the quantum metric, averaged over the Brillouin zone, characterizes the shape of the pair correlation function.

Induction of new ferrielectric smectic phases in the electric field

ABSTRACTA theoretical approach for the description of intermediate phase sequences (observed in the temperature range between Sm-C* and Sm-CA*) in the presence of electric field is derived. The induction of long-periodicity ferrielectric smectic phases by the electric field is discussed. In particular, we acknowledge the induction of the 12-layer and 15-layer periodicity subphases, whose structure coincides with the ones observed by resonant x-ray scattering in [A. Iida, I. Nishiyama, and Y. Takanishi, Phys. Rev. E 89, 032503 (2014)].

Polar Order and Frustrated Antiferromagnetism in Perovskite Pb2MnWO6 Single Crystals.

Single crystals of the multiferroic double-perovskite Pb2MnWO6 have been synthesized and their structural, thermal, magnetic and dielectric properties studied in detail. Pure perovskite-phase formation and stoichiometric chemical composition of the as-grown crystals are confirmed by X-ray single-crystal and powder diffraction techniques as well as energy-dispersive X-ray and inductively coupled plasma mass spectrometry. Detailed structural analyses reveal that the crystals experience a structural phase transition from the cubic space group (s.g.) Fm3̅m to an orthorhombic structure in s.g. Pn21a at about 460 K. Dielectric data suggest that a ferrielectric phase transition takes place at that same temperature, in contrast to earlier results on polycrystalline samples, which reported a transition to s.g. Pnma and an antiferroelectric low-temperature phase. Magnetic susceptibility measurements indicate that a frustrated antiferromagnetic phase emerges below 8 K. Density functional theory based calculations confirm that the cationic order between Mn and W is favorable. The lowest total energy was found for an antiferromagnetically ordered state. However, analyses of the calculated exchange parameters revealed strongly competing antiferromagnetic interactions. The large distance between the magnetic atoms, together with magnetic frustration, is shown to be the main reason for the low value of the ordering temperature observed experimentally. We discuss the structure-property relationships in Pb2MnWO6 and compare these observations to reported results on related Pb2BWO6 perovskites with different B cations.

Giant barocaloric effects at low pressure in ferrielectric ammonium sulphate.

Caloric effects are currently under intense study due to the prospect of environment-friendly cooling applications. Most of the research is centred on large magnetocaloric effects and large electrocaloric effects, but the former require large magnetic fields that are challenging to generate economically and the latter require large electric fields that can only be applied without breakdown in thin samples. Here we use small changes in hydrostatic pressure to drive giant inverse barocaloric effects near the ferrielectric phase transition in ammonium sulphate. We find barocaloric effects and strengths that exceed those previously observed near magnetostructural phase transitions in magnetic materials. Our findings should therefore inspire the discovery of giant barocaloric effects in a wide range of unexplored ferroelectric materials, ultimately leading to barocaloric cooling devices.

Manipulation of Dy-Mn coupling and ferrielectric phase diagram of DyMn2O5: The effect of Y substitution of Dy

DyMn2O5 is an extraordinary example in the family of multiferroic manganites and it accommodates both the 4f and 3d magnetic ions with strong Dy-Mn (4f-3d) coupling. The electric polarization origin is believed to arise not only from the Mn spin interactions but also from the Dy-Mn coupling. Starting from proposed scenario on ferrielectricity in DyMn2O5 where the exchange-strictions associated with the Mn3+-Mn4+-Mn3+ blocks and Dy3+-Mn4+-Dy3+ blocks generate the two ferroelectric sublattices, we perform a set of characterizations on the structure, magnetism, and electric polarization of Dy1-xYxMn2O5 in order to investigate the roles of Dy-Mn coupling in manipulating the ferrielectricity. It is revealed that the non-magnetic Y substitution of Dy suppresses gradually the Dy3+ spin ordering and the Dy-Mn coupling. Consequently, the ferroelectric sublattice generated by the exchange striction associated with the Dy3+-Mn4+-Dy3+ blocks is destabilized, but the ferroelectric sublattice generated by the exchange striction associated with the Mn3+-Mn4+-Mn3+ blocks remains less perturbed, enabling the ferrielectricity-ferroelectricity transitions with the Y substitution. A phenomenological ferrielectric domain model is suggested to explain the polarization reversal induced by the Y substitution. The present work presents a possible scenario of the multiferroic mechanism in not only DyMn2O5 but probably also other RMn2O5 members with strong 4f-3d coupling.

Ferrielectric phase in the (Bi1/2Na1/2)TiO3–Ba(Mg1/3Nb2/3)O3 system

We have investigated the crystal structure of (1 − x)(Bi1/2Na1/2)TiO3–xBa(Mg1/3Nb2/3)O3 (BNT–BMN) by high-resolution neutron powder diffraction (NPD) analysis. Our NPD study combined with polarization hysteresis measurements for ceramics reveals that a boundary between rhombohedral R3c and tetragonal P4bm phases exists at x = 4–5%. The Rietveld analysis of the NPD data shows that the crystal structure with x = 10% has a single-phase tetragonal structure in space group P4bm, as has been reported for BNT–7%BaTiO3. The P4bm structure exhibits antiparallel displacements of A- and B-site cations, which results in a small spontaneous polarization (Ps) of 13.3 µC/cm2 (estimated from the refined structural parameters). The results obtained for BNT–10%BMN ceramics strongly suggest ferrielectric features; the application of electric fields induces a transition from the P4bm phase with a small Ps to other ferroelectric phases with a large Ps.

Dielectric Behavior of Monoclinic Rb(H0.7D0.3)2PO4 under Constant Hydrostatic Pressure

The dielectric constant of monoclinic Rb(H0.7D0.3)2PO4 was measured in a temperature range covering the ferrielectric phase transition temperature at various hydrostatic pressures below 0.45 GPa. All the dielectric constant showing a pronounced deviation from the Curie-Weiss law was analyzed successfully by the expression on the basis of the quasi-one-dimensional Ising model. The characteristic parameters Γ, B and ξ in the theoretical expression were estimated at various pressures for Rb(H0.7D0.3)2PO4. The pressure derivative of characteristic parameters dΓ/dp, dB/dp and dξ/dp were estimated to be −311 K/GPa, −0.4 K/GPa and −48 (GPa)−1, respectively.

Structure and properties of nonwoven materials based on copolymer of tetrafluoroethylene and vinyldenefluoride produced by aerodynamic formation

Properties of nonwoven materials based on copolymer of tetrafluoroethylene and vinyldenefluoride produced by aerodynamic formation in a turbulent gas flow are investigated in the paper. By means of scanning microscopy, it is shown that synthesized nonwoven materials are characterized by high porosity and complicated spatial organization. By means of X-ray diffraction, infrared spectroscopy, combination scattering spectroscopy, thermogravimetric analysis, and differential scanning calorimetry, it is shown that fibers that form the nonwoven material are characterized by a crystal structure typical of ferrielectric phases. The quantitative content of residual solvents in the formed materials is determined. By using a mobile cell culture, it is shown that the produced nonwoven materials are not toxic and can be used for medical purposes.

Chiral smectic transition phases appearing near the electric-field-induced phase transition observed by resonant microbeam x-ray scattering.

The electric-field-induced phase transition of a chiral liquid crystal containing Br revealed a transition phase between the three-layer periodicity ferrielectric phase and the synclinic ferroelectric phase in the electric field versus temperature phase diagram. Resonant x-ray scattering from the transition phase showed a diffuse streak or spotty weak reflections, which were composed of strong m/3-order (where m = 1 and 2) reflections and other weak peaks. The spotty reflections were found to be related to a 12-layer periodicity phase with a weak contribution from the 15-layer periodicity. An x-ray intensity analysis based on the Ising model suggested that the 12-layer periodicity phase was composed of two three-layer ferrielectric blocks and six synclinic layers. This model indicated that, in the transition phase, the three-layer ferrielectric molecular configuration gradually changed to the synclinic configuration. The diffuse streak appearing around m/3-order reflections near the field-induced transition from the four-layer periodicity phase to the synclinic ferroelectric phase is also discussed.

Crystal and magnetic structures of hexagonal YMnO3

The available data on the structural and magnetic transitions in multiferroic hexagonal YMnO3 have been reviewed, first making use of the computer programs from the group theoretical ISOTROPY software suite to list possible crystal and magnetic structures, then taking into account the capability of neutron diffraction and other physical methods to distinguish them. This leads to a clear view of the transformation sequence, as follows. Hexagonal YMnO3 is paraelectric in P63/mmc at elevated temperatures, and undergoes a single structural transition on cooling through 1250 K to a ferrielectric phase in P63cm that is retained through room temperature. At a much lower temperature, 70 K, there is a magnetic transition from paramagnetic to a triangular antiferromagnetic arrangement, most likely with symmetry P63'cm'. Comment is made on the unusual coupling of ferroelectric and magnetic domains reported to occur in this material, as well as on the so-called `giant magneto-elastic' effect.