Ferroelectric-paraelectric Phase Transition Research Articles

Molecular Ferroelectric Pyridin-4-ylmethanaminium Perchlorate Undergoes Paraelectric–Ferroelectric and Ferroelectric–Ferroelectric Phase Transitions

Molecule-based ferroelectrics are a class of highly desirable intelligent materials for their rich switchable physical properties, easy and environmentally friendly processing, especial lightweight and mechanical flexibility. In the current work, a new molecule-based ferroelectrics pyridin-4-ylmethanaminium perchlorate was discovered undergoing paraelectric–ferroelectric phase transition at Tc = 258.40(8) K and ferroelectric–ferroelectric phase transition at T1 = 255.93(2) K. It crystallizes in monoclinic crystal system with a centrosymmetric space group of C2/c at 293 K and also crystallizes in monoclinic crystal system but with a polar space group of Cc at 223 K. The spontaneous polarization can reach 1.25 μC/cm2 and the coercive field is about 2.6 kV/cm below 254 K. The paraelectric–ferroelectric phase transition belongs to displacive phase transition and the nearby ferroelectric–ferroelectric phase transition contains order–disorder features, which consistent with the dynamic process including deforma...

Studies of Phase Transitions and Magnetoelectric Coupling in PFN-CZFO Multiferroic Composites

We report studies of the ferroelectric and magnetic phase transitions of (1 – x)Pb(Fe0.5Nb0.5)O3 – xCo0.65Zn0.35Fe2O4 (x = 0.2) composite with emphasis upon the nature of magnetoelectric coupling at room temperature. The presence of all cationic elements with their required stoichiometry have been confirmed by SEM and XPS studies. The composite shows well-saturated ferroelectric and ferromagnetic (multiferroic) behavior at room temperature. A ferroelectric-paraelectric phase transition has been confirmed from the temperature dependent dielectric spectra along with DSC and Raman spectroscopic studies. Antiferromagnetic, ferromagnetic, and relaxor paramagnetic states have been observed in this composite. This composite shows strong bulk biquadratic magnetoelectric coupling at room temperature, which can be useful for potential multifunctional device applications.

Ferroelectricity and magnetism in metal-formate frameworks of [NH4][M(HCOO)3] (M = Sc to Zn): a first-principles study

A comprehensive first-principles calculations reveal the multiferroicity and tunable magnetism via carrier doping in [NH4][M(HCOO)3] (M = 3d transition metal).

High pressure single crystal x-ray and neutron powder diffraction study of the ferroelectric–paraelectric phase transition in PbTiO3

The results obtained by high pressure neutron powder diffraction and single-crystal x-ray diffraction for the P4mm–Pmm phase transition in the prototype ferroelectric perovskite lead titanate are shown. Neutron diffraction is found to be strongly sensitive to the dipolar moment in the PbTiO3 unit cell due to the gradual reduction of the displacement of the Ti and O atoms from centrosymmetric positions in the cubic perovskite structure which exhibits anti-phase scattering of Pb, Ti and O atoms. From applying both techniques, the anomalously high Debye–Waller factor for the lead atoms confirms the disordered character of the cubic phase. High pressure single crystal x-ray diffraction also perfectly describes the ferroelectric–paraelectric transition and will be the technique of choice to solve higher pressure structures for PbTiO3.

Quantitative Analysis of the Local Phase Transitions Induced by Laser Heating.

Functional imaging enabled by scanning probe microscopy (SPM) allows investigations of nanoscale material properties under a wide range of external conditions, including temperature. However, a number of shortcomings preclude the use of the most common material heating techniques, thereby limiting precise temperature measurements. Here we discuss an approach to local laser heating on the micron scale and its applicability for SPM. We applied local heating coupled with piezoresponse force microscopy and confocal Raman spectroscopy for nanoscale investigations of a ferroelectric-paraelectric phase transition in the copper indium thiophosphate layered ferroelectric. Bayesian linear unmixing applied to experimental results allowed extraction of the Raman spectra of different material phases and enabled temperature calibration in the heated region. The obtained results enable a systematic approach for studying temperature-dependent material functionalities in heretofore unavailable temperature regimes.

Microdomain dynamics in single-crystalBaTiO3during paraelectric-ferroelectric phase transition measured with time-of-flight neutron scattering

Microscopic polar clusters can play an important role in the phase transition of ferroelectric perovskite oxides such as $\mathrm{BaTi}{\mathrm{O}}_{3}$, which have shown coexistence of both displacive and order-disorder dynamics, although their topological and dynamical characteristics are yet to be clarified. Here, we report sharp increases in the widths and intensities of Bragg peaks from a $\mathrm{BaTi}{\mathrm{O}}_{3}$ single crystal, which are measured in situ during heating and cooling within a few degrees of its phase transition temperature ${T}_{C}$, using the neutron time-of-flight Laue technique. Most significantly sharper and stronger increases in peak widths and peak intensities were found to occur during cooling compared to that during heating through ${T}_{C}$. A closer examination of the Bragg peaks revealed their elongated shapes in both the paraelectric and ferroelectric phases, the analysis of which indicated the presence of microdomains that have correlated $\ensuremath{\langle}111\ensuremath{\rangle}$-type polarization vectors within the {110}-type crystallographic planes. No significant increase in the average size of the microdomains $(\ensuremath{\sim}10\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$ near ${T}_{C}$ could be observed from diffraction measurements, which is also consistent with small changes in the relaxation times for motion of Ti ions measured with quasielastic neutron scattering. The current observations do not indicate that the paraelectric-ferroelectric phase transition in $\mathrm{BaTi}{\mathrm{O}}_{3}$ is primarily caused by an increase in the size of the microscopic polar clusters or critical slowing down of Ti ionic motion. The sharp and strong increases in peak widths and peak intensities during cooling through ${T}_{C}$ are explained as a result of microstrains that are developed at microdomain interfaces during paraelectric-ferroelectric phase transition.

Magnetic Augment in the Nitrogen Substituted Bismuth Ferrite

The nitrogen substituted bismuth ferrite polycrystal sample BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.1</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> has been successfully synthesized using sol-gel method. Its structural and magnetic properties are investigated. The formation of Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> due to charge compensation is found in BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.1</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> from X-ray photoelectron spectra. The crystal structure of BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is barely affected by N doping while the magnetic property is well improved. We propose that it is the coexistence of different superexchanges (Fe-N-Fe and Fe-O-Fe) that breaks the magnetic cancellation effect of the spin spiral, hence increasing the macroscopic magnetization.

Direct transition from the rhombohedral ferroelectric to the paraelectric phase in a (Ba,Sr)TiO3 thin film on a (111)MgO substrate

A heteroepitaxial (200 nm thick) (BST) thin film was deposited on a (111)MgO substrate using rf sputtering. X-ray diffraction examinations confirmed epitaxial growth and rhombohedral symmetry of the film ( and ) at room temperature. Polarized Raman spectra of the film were studied in the temperature range from 100 to 420 K. In contrast to a BST thin film grown on (001)MgO, the observed linear temperature dependence of the squared soft mode frequency suggests the displacive character of the ferroelectric-paraelectric phase transition in a BST thin film on (111)MgO.

Effect of temperature on loss mechanism of 0.7PMN–0.3PZT ceramics

In this work, 0.7Pb(Mg1/3Nb2/3)O3-0.3Pb(Zr0.52Ti0.48)O3 (0.7PMN–0.3PZT) relaxor ferroelectric ceramic was prepared. The dielectric constant was measured by LCR meter at frequencies of 1–100kHz to observe ferroelectric–paraelectric phase transition Tm. To investigate effect of temperature on loss mechanism, 0.7PMN–0.3PZT ceramic was subjected to measurement electric field induced strain and polarization behavior at 0.2Hz and 0.05Hz by modified Michelson interferometric technique and Sawyer-Tower circuit with temperatures between 30°C and 50°C. The result showed dielectric constant peak at around 50°C. The hysteresis of polarization and induced strain decreased to slimmer loop when temperature increased, where polarization hysteresis shows anti-clockwise direction when measured at 0.2Hz but clockwise at 0.05Hz of applied electric field frequency at subswitching field 6kV/cm due to frequency dependence of electrical loss and caused accumulated depolarizing field inside material when lower spontaneous polarization appears to be temperature dependent. The change of linear polarization from positive to negative when the frequency was decreased contributed to a decrease of induced-strain and this is promising for application of actuators.

Effect of Bismuth Doping on the Dielectric and Piezoelectric Properties of Ba1-xBixTiO3 Lead-Free Ceramics

In this paper we report the dielectric and piezoelectric properties of Bi modified Ba1-xBixTiO3 lead-free ceramics. These ceramic samples were synthesized by conventional solid state reaction method. The XRD spectra recorded at room temperature (RT) suggested decrease in the tetragonality (c/a) for Bi doped derivatives with the presence of minor rhombohedral phase for heavily doped specimens. The grain boundary pinning occurring in slightly Bi-doped derivative (x = 0.025) was found to reduce the grain size to submicron regime. However, for higher Bi doping the presence of liquid phase led to the grain coarsening. The doped derivatives exhibited shifting of the paraelectric-ferroelectric (PE-FE) phase transition towards RT with rather diffused Curie peak. The substitution of Bi3+ (with different ionic radii and electronegativity) on A-site of ABO3 structure resulted in regions with modified polar structure giving rise to diffused PE-FE phase transition. The specimen with x = 0.025 exhibited enhanced planar electro-mechanical coupling constant (kp) ∼ 25% with longitudinal piezoelectric constant (d33) of ∼112 pC/N. The sample with x = 0.025 also exhibited 0.085% electric-field induced strain along with the remnant polarization (2Pr) of ∼15 μC/cm2 and coercive field (2Ec) of ∼22 kV/cm. The increased Ec with reasonable Pr is an important material characteristics for the stable functionality of the memory devices.

Investigation of the Physical Properties of PLZT Ferroelectric Ceramics – Effect of the Lanthanum Content

In this work, the structural, ferroelectric and dielectric properties, including radio-frequencies and microwave region, has been investigated in Pb1 − xLax(ZryTi1 − y)1 − (x/4)O3 (PLZT) ferroelectric ceramics, where x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12 and y = 0.70. Ceramic samples were obtained from the solid-state reaction sintering method, and the dielectric measurements were performed in a wide frequency and temperature region, below and above the paraelectric-ferroelectric (PE-FE) phase transition temperature. The structural properties, investigated at room temperature, from the x-ray diffraction (XRD) technique, revealed the evolution from the rhombohedral (R3m symmetry) to orthorhombic (Pmmm symmetry) phases, with the increase of the lanthanum concentration. The ferroelectric as well as the low frequency dielectric properties revealed a change in the PE-FE phase transition characteristics from a normal to a relaxor behavior, with the increase of the lanthanum content. On the other hand, the high-frequency (microwave) dielectric properties studied at room temperature, showed a strong dielectric dispersion on both normal (x≤0.06) and relaxor (x>0.06) compositions, which indeed revealed to be also strongly dependent on the lanthanum concentration.

Phase Transition Characteristics in A-Site La3+ Modified Bi-Layered Aurivillius-Type Structure SrBi2Nb2O9 Ferroelectric Ceramics

The phase transition characteristics have been investigated in lanthanum modified bismuth layer structured SrBi2Nb2O9 (SBN) ferroelectric ceramics, obtained from the conventional sintering method. In particular, structural, ferroelectric and dielectric properties have been analyzed taking into account the influence of the lanthanum content. Results of Raman spectroscopy as well as dielectric response suggested an evolution from normal ferroelectric-paraelectric phase transition to a relaxor-like behavior of the SLBN system, with the increase of the lanthanum concentration. The compositional cationic disorder has been considered as the main cause for the observed behavior, affecting the evolution of the long-rage polar ordering in the studied system.

Effect of temperature on the efficiency of organometallic perovskite solar cells

In recent years perovskite solar cells have attracted an increasing scientific and technological interest in the scientific community. It is important to know that the temperature is one of the factors which have a strong effect on the efficiency of perovskite solar cell. This study communicates a temperature analysis on the photovoltaic parameters of CH3NH3PbI3-based perovskite solar cell in a broad interval from 80 to 360 K. Strong temperature-dependent photovoltaic effects have been observed in the type of solar cell, which could be mainly attributed to CH3NH3PbI3, showing a ferroelectric-paraelectric phase transition at low temperature (T < 160 K). An increase in temperature over the room temperature decreased the perovskite solar cell performance and reduced its efficiency from 16% to 9%. The investigation with electronic impedance spectroscopy reveals that at low temperature (T < 120 K) the charge transport layer limits the device performance, while at high temperature (T > 200 K), the interfacial charge recombination becomes the dominant factor.

Microstructure and Electrical Properties of Eu-Doped K0.5Na0.5NbO3 Ceramics

(K0.5Na0.5)1–3xEuxNbO3 (0≤x≤0.05) lead-free ceramics have been prepared by a conventional solid state reaction. XRD show that the ceramics possess a pure perovskite structure with orthorhombic symmetry. Dopant Eu restrains the grain growth, decreases the ferroelectric-paraelectric phase transition temperature and leads to a diffuse phase transition. With the increase of Eu, the observed remanent polarization (Pr) decreases while the coercive field (Ec) remains almost unchanged. Nevertheless, for the increase in relative permittivity, the sample with x = 0.005 exhibits the optimum piezoelectric properties, giving a large piezoelectric coefficient (d33 = 121 pC/N) and a high planar electromechanical coupling coefficient (kp = 0.41).

Monitoring and understanding the paraelectric-ferroelectric phase transition in the metal-organic framework [NH4 ][M(HCOO)3 ] by solid-state NMR spectroscopy.

The paraelectric-ferroelectric phase transition in two isostructural metal-organic frameworks (MOFs) [NH4 ][M(HCOO)3 ] (M=Mg, Zn) was investigated by in situ variable-temperature (25) Mg, (67) Zn, (14) N, and (13) C solid-state NMR (SSNMR) spectroscopy. With decreasing temperature, a disorder-order transition of NH4 (+) cations causes a change in dielectric properties. It is thought that [NH4 ][Mg(HCOO)3 ] exhibits a higher transition temperature than [NH4 ][Zn(HCOO)3 ] due to stronger hydrogen-bonding interactions between NH4 (+) ions and framework oxygen atoms. (25) Mg and (67) Zn NMR parameters are very sensitive to temperature-induced changes in structure, dynamics, and dielectric behavior; stark spectral differences across the paraelectric-ferroelectric phase transition are intimately related to subtle changes in the local environment of the metal center. Although (25) Mg and (67) Zn are challenging nuclei for SSNMR experiments, the highly spherically symmetric metal-atom environments in [NH4 ][M(HCOO)3 ] give rise to relatively narrow spectra that can be acquired in 30-60 min at a low magnetic field of 9.4 T. Complementary (14) N and (13) C SSNMR experiments were performed to probe the role of NH4 (+) -framework hydrogen bonding in the paraelectric-ferroelectric phase transition. This multinuclear SSNMR approach yields new physical insights into the [NH4 ][M(HCOO)3 ] system and shows great potential for molecular-level studies on electric phenomena in a wide variety of MOFs.

Effect of sintering temperature and oxygen atmosphere on electrocaloric effect of BaTiO3 ceramics

This paper demonstrates the effect of sintering parameters on the electrocaloric effect (ECE) in BaTiO3 ferroelectric ceramics, especially the sintering temperature and atmosphere. The samples were prepared by solid-state reaction method. With the rise of sintering temperature from 1200 °C to 1350 °C, the grain size increases remarkably and the densification is improved. The 1350 °C sintered sample has better ferroelectricity and higher latent heat for ferroelectric-paraelectric phase transition than those of the 1200 °C sintered sample. Correspondingly, it exhibits much better ECE. If the sample is sintered in pure oxygen, instead of in air, all ferroelectricity, dielectric strength and ECE are further enhanced. The sample sintered at 1350 °C in oxygen exhibits an excellent ECE performance with ΔT max = 1.37 K and ΔS max = 1.75 J/kg K.

Ac conductivity and ferroelectric phase transition of Bi0.7(Ba0.8Sr0.2)0.3Fe0.7Ti0.3O3 ceramic

The Bi0.7(Ba0.8Sr0.2)0.3Fe0.7Ti0.3O3 ceramic is synthesized by a solid state reaction method and characterized by X-ray diffraction (XRD), SEM, Raman spectra and impedance spectroscopy. Besides, the XRD pattern shows perovskite phase with rhombohedral structure (R3c space group) at room temperature. Furthermore, the ferroelectric-paraelectric phase transition (TC) and G-type antiferromagnetic Neel temperature (TN) is detected by Raman spectroscopy. Meanwhile, the electrical conductivity of the sample is investigated in the temperature and the frequency range 713–773K and 100–1000kHz respectively by means of impedance spectroscopy. The Nyquist plots (−Z″ versus Z′) frequency plots are well fitted to an equivalent circuit model. The ac conductivity data obey the universal power law. The nature of variation of dc conductivity suggests Arrhenius type of electrical conductivity. The temperature dependence of the alternative current conductivity (σg) and direct current conductivity (σdc) confirm the presence of the ferroelectric–paraelectric phase transition.

Phenomenological theory of magnetoelectric coupling in granular multiferroics

We study coupling between the ferroelectric polarization and magnetization of granular ferromagnetic film using a phenomenological model of combined multiferroic system consisting of granular ferromagnetic film placed above the ferroelectric (FE) layer. The coupling is due to screening of Coulomb interaction in the granular film by the FE layer. Below the FE Curie temperature the magnetization has hysteresis as a function of electric field. Below the magnetic ordering temperature the polarization has hysteresis as a function of magnetic field. We study the magneto-electric coupling for weak and strong spatial dispersion of the FE layer. The effect of mutual influence decreases with increasing the spatial dispersion of the FE layer. For weak dispersion the strongest coupling occurs in the vicinity of the ferroelectric-paraelectric phase transition. For strong dispersion the situation is the opposite. We study the magneto-electric coupling as a function of distance between the FE layer and the granular film. For large distances the coupling decays exponentially due to the exponential decrease of electric field produced by the oscillating charges in the granular ferromagnetic film.

Ferroelectric-Paraelectric Phase Transition of CsH2PO4studied by Static NMR and MAS NMR

The microscopic dynamics of CsH2PO4, with two distinct hydrogen bond lengths, are studied by static nuclear magnetic resonance (NMR) and magic angle spinning (MAS) NMR. The proton dynamics of the two crystallographically inequivalent hydrogen sites were discussed in terms of the 1 H

Order-disorder type critical behavior at the magnetoelectric phase transition in multiferroicDyMnO3

We present the results of detailed dielectric investigations of the relaxation dynamics in ${\mathrm{DyMnO}}_{3}$ multiferroic manganite. A strong low-frequency relaxation process near the paraelectric-ferroelectric phase transition is observed. We provide experimental evidence to show that this relaxation mode corresponds to a chirality switching of the spin cycloid in ${\mathrm{DyMnO}}_{3}$. We demonstrate that the relaxation dynamics in ${\mathrm{DyMnO}}_{3}$ is typical for an order-disorder phase transition and may be understood within a simple model with a double-well potential. These results suggest the interpretation of the paraelectric sinusoidal phase in manganites as a dynamical equilibrium of magnetic cycloids with opposite chiralities.