Mean-Field Behavior of the Paraelectric-Ferroelectric Phase Transition of a Fluorinated Compound
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The partially fluorinated MHPOBC analogue (MHPO(F)PBC) shows an attractive phase sequence: SmA*, SmC f *, SmC* and SmC A *. The SmC f * phase was only observed by reversal current switching method. Measurements of spontaneous polarization P s (T) reveal the existence of the SmC f * sub-phase between the SmA* and SmC* phases. Linear dielectric spectroscopy studies corroborate almost model behavior of the soft mode relaxation frequency - obtained under bias field of 20V/20 w m -in the vicinity of the SmA*-SmC* phase transition. Keywords: Ferroelectric And Antiferroelectric Liquid CrystalsDielectric SpectroscopyAntiferroelectric ModesSpontaneous PolarizationPhase TransitionsKeywords:
Ferroics
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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Abstract The paper reviews the results of experimental and theoretical studies of ferroic phase transitions in β-LiNH4SO4 and its deuterated analogue. β-LiNH4SO4 undergoes succesive phase transitions: a paraelectric - ferroelectric phase transition at T1 ≃ 462 K, a ferroelectric - ferroelastic phase transition at T2 ≃ 283 K and a transition from one ferroelastic phase to the other at T3 ≃ 28 K. Attention is focused on the influence of the order of phase transitions on the pattern of ferroelectric and ferroelastic domain structure, and also on the role played by the dynamics of molecular groups in the mechanism of transitions. The pre-transition effect connected with the ferroelectric-paraelectric transition: heterophase, capable of accounting for anomalies in different physical properties present 1-3 K below T1 is shown. The anomalous temperature variation of spontaneous polarisation of the crystal is discussed within the framework of the phenomenological model of weak ferroelectrics.
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Ferroelasticity
Phenomenological model
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Solid-state physics
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Abstract Abstract Structural phase transition in CsZnPO4 crystal has been studied with X-ray diffraction technique. A new phase transition has been found to take place at a transition temperature T 3=200K on cooling from a room temperature phase (the phase III) to a new phase which is called the phase IV. Characteristic point of this phase transition is that it is a typical first-order phase transition and it takes a very long time to accomplish the phase change. When sample is rapidly quenched from a starting temperature T s=205K in the phase III to a final temperature T f=19K in the phase IV through T3, it takes about 3 days to accomplish the phase transition. Key Words: slow phase transitionfirst-order phase transitionX-ray diffraction
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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.
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Atmospheric temperature range
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Two-step phase transition model, displacive to order-disorder, is proposed. The driving forces for these two transitions are fundamentally different. The displacive phase transition is one type of the structural phase transitions. We clearly define the structural phase transition as the symmetry broking of the unit cell and the electric dipole starts to form in the unit cell. Then the dipole-dipole interaction takes place as soon as the dipoles in unit cells are formed. We believe that the dipole-dipole interaction may cause an order-disorder phase transition following the displacive phase transition. Both structural and order-disorder phase transition can be first-order or second-order or in between. We found that the structural transition temperatures can be lower or equal or higher than the order-disorder transition temperature. The para-ferroelectric phase transition is the combination of the displacive and order-disorder phase transitions. It generates a variety of transition configurations along with confusions. In this paper, we discuss all these configurations using our displacive to order-disorder two-step phase transition model and clarified all the confusions.
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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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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.
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Ferroelectric Polymers
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Abstract Phase transition materials are attractive from the viewpoints of basic science as well as practical applications. For example, optical phase transition materials are used for optical recording media. If a phase transition in condensed matter could be predicted or designed prior to synthesizing, the development of phase transition materials will be accelerated. Herein we show a logical strategy for designing a phase transition accompanying a thermal hysteresis loop. Combining first-principles phonon mode calculations and statistical thermodynamic calculations considering cooperative interaction predicts a charge-transfer phase transition between the A–B and A + –B − phases. As an example, we demonstrate the charge-transfer phase transition on rubidium manganese hexacyanoferrate. The predicted phase transition temperature and the thermal hysteresis loop agree well with the experimental results. This approach will contribute to the rapid development of yet undiscovered phase transition materials.
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Rubidium
Hysteresis
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