Diffuse phase transitions in thick ferroelectric Ba(TixSn1−x)O3 films of perovskite-type structure
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The pressure-induced structural phase transitions of e- and γ-CL-20 were studied by Raman and mid-infrared spectroscopy up to 60 GPa. In this work, the phase transition of CL-20 from the e-phase to the γ′-phase starts at 0.9 GPa and ends at 4.4 GPa. The γ′-phase in this work is distinctly different from the γ-phase recognized by the energetic community in terms of the structure and properties. Subsequently, the η phase starts at 6.9 GPa and ends at 10.6 GPa because of the slight cage distortion. With further increase of the loading pressure, two new phases, φ and ι, were observed at 28 and 50 GPa, respectively. The infrared results are consistent with Raman results and show that similar phase regions are observed for CL-20 under high pressures. The behavior of the γ-phase under pressure indicates that the ζ-phase appears at 1.3 GPa and sustains its stability up to 47.4 GPa. The current results prove that the newly discovered γ′-phase is evidently distinct from the γ-phase and they undergo different phase transition routes under loading compression.
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Investigation of the Ferroelectric Paraelectric Phase Transition in Bulk and Confined Sodium Nitrite
Levanyuk-Sannikov model is used to describe the ferroelectric-paraelectric transition in bulk and confined sodium nitrite (NaNO2). It is found on the basis of this model that the phase transition of NaNO2 for the bulk material is weakly first order whereas for the confined material it is a second order transition. Calculations are performed and the fitted parameters are obtained using this model for the ferroelectric-paraelectric transition in NaNO2. Our results indicate that the Levanyuk-Sannikov model describes adequately the observed behaviour of the ferroelectric-paraelectric transition in NaNO2.
Sodium nitrite
Transition temperature
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The authors of paper commented claim that trimethylammonium tetrachlorozincate crystal shows at 282 K the ferroelectric-paraelectric phase transition. But no ferroelectric hysteresis loop was observed below this temperature. Moreover, in the low-temperature phase the ferroelectric domain walls should exist giving dielectric relaxation in a low frequency electric field. The authors conclude that the phase transition is of the second order. This conclusion is contrary to the DSC data where the phase transition has a strong first order character. In the whole measured temperature range the dielectric loss is 100 times higher than the real part of dielectric constant.
Hysteresis
Atmospheric temperature range
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Geometric ferroelectrics are called as improper ferroelectrics where geometric structural constraints, rather than typical cation-anion paring, induce proper ferroelectric polarization. Hybrid improper ferroelectricity, one kind of geometric ferroelectricity, results from the combination of two or more of non-ferroelectric structural order parameters. In recent, hybrid improper ferroelectricity has been theoretically predicted in ordered perovskites and the Ruddlesden-Popper compounds. However, the ferroelectricity of these compounds has never been experimentally confirmed and even their polar nature has been under debate. In this talk, we report our experimental results of exploring switchable electric polarization and domain structures in the single crystals of the n = 2 layered Ruddlesden-Popper compounds.
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Vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymers are ferroelectric materials and exhibit ferroelectric to paraelectric phase transitions. In order to understand the ferroelectric phase transition of polymers, we performed Monte Carlo simulations for the three states model which an extra freedom was added to Ising model. The simulations reproduced the characters of the ferroelectric phase transition of VDF/TrFE copolymers. The temperature dependence of the specific heat obtained by MC simulations revealed that the transition changed from a first order transition to a diffuse one and that the critical phenomena existed between them. Keywords: Ferroelectric phase transitionMonte Carlo simulationspecific heatVDF-TrFE copolymer Acknowledgments Paper originally presented at IMF-11, Iguassu Falls, Brazil, September 5–9, 2005; received for publication January 26, 2006.
Ferroelectric Polymers
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Based on first-principles calculations, we discover two new two-dimensional (2D) ferroelectric materials SbN and BiP. Both of them are stable in a phosphorene-like structure and maintain their ferroelectricity above room temperature. Till date, SbN has the largest in-plane spontaneous polarization of about 7.81 × 10-10 C m-1 ever found in 2D ferroelectric materials, and it can retain its ferroelectricity until melting at about 1700 K. The spontaneous polarizations and switching barriers can easily be tuned by strains. Additionally, the ferroelectricity can still be maintained in their multilayers. These advantages make SbN and BiP promising candidate materials for future integrated ferroelectric devices.
Phosphorene
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The ferroelectric phase transition characteristics of the 0.32Pb(In1/2Nb1/2)O3-0.345Pb(Mg1/3Nb2/3)O3-0.335PbTiO3 (0.32PIN-0.345PMN-0.335PT) single crystals were studied by the temperature-dependent Raman spectroscopy and some electrical properties. Ferroelectric monoclinic phase was confirmed at room temperature by the numbers of the Raman modes. Successive ferroelectric phase transitions, i.e. ferroelectric monoclinic phase to ferroelectric tetragonal phase transition (FEM-FET) and ferroelectric tetragonal phase to paraelectric cubic phase transition (FET-PC), are evidenced by the anomalies of Raman modes line width, peaks intensity and their ratios around TM-T and TC/Tm temperatures. The temperature dependent permittivity derivative ξ = dϵ/dT not only provides further evidence of the successive ferroelectric phase transitions, but also demonstrates the second-order transition characteristic of the FEM-FET phase transition and the first-order transition feature of the FET-PC phase transition. The FEM-FET phase transition is also confirmed by the abnormal narrowing of the P-E loops, decrease of the Pr and Ec values, and extremums of the pyroelectric performance.
Tetragonal crystal system
Monoclinic crystal system
Transition temperature
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Ferroelectric materials are a special type of polar substances, including solids or liquid crystals. However, obtaining a material to be ferroelectric in both its solid crystal (SC) and liquid crystal (LC) phases is a great challenge. Moreover, although cholesteric LCs inherently possess the advantage of high fluidity, their ferroelectricity remains unknown. Here, through the reasonable H/F substitution on the fourth position of the phenyl group of the parent nonferroelectric dihydrocholesteryl benzoate, we designed ferroelectric dihydrocholesteryl 4-fluorobenzoate (4-F-BDC), which shows ferroelectricity in both SC and cholesteric LC phases. The fluorination induces a lower symmetric polar P1 space group and a new solid-to-solid phase transition in 4-F-BDC. Beneficial from fluorination, the SC and cholesteric LC phases of 4-F-BDC show clear ferroelectricity, as confirmed by well-shaped polarization-voltage hysteresis loops. The dual ferroelectricity in both SC and cholesteric LC phases of a single material was rarely found. This work offers a viable case for the exploration of the interplay between ferroelectric SC and LC phases and provides an efficient approach for designing ferroelectrics with dual ferroelectricity and cholesteric ferroelectric liquid crystals.
Antiferroelectricity
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Abstract The structural phase transition between phase P and phase R in NaNbO 3 single crystals was studied by an optical method. It was found that this transition is similar to the martensitic transformation and that the phase fronts are formed by crystallographic planes having indices close to {0.2.11}. Behind the simple phase front a monodomain state arises. The polydomain state is the resultant of complex phase fronts.
Ferroics
R-Phase
Ferroelasticity
Diffusionless transformation
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High pressure ultrasonic and D - E hystresis measurements were performed on a vinylidene fluoride-trifluoroethylene (VDF/TrFE) copolymer with 54 mol% VDF content to investigate the pressure effect on physical properties accompanying wiht a ferroelectric phase transition. Differing from the results at atmospheric pressure where the ferro-to-paraelectric phase transition proceeded simply in one-step, this copolymer exhibited at 350 MPa two-step temperature variations in ultrasonic velocity and absorption, and remanent polarization upon the ferroelectric phase transition. These results agree well with the previous results of DTA and X-ray diffraction experiments, suggesting that the changes in the nature of the ferroelectric phase transition is attributed to the pressure-induced structural transformation.
Transition temperature
Ferroelectric Polymers
Ferroics
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