Ferroelectric Phase Transition Research Articles

Study of dielectric properties of nanocrystalline material BaTiO3-SiO2

Within the temperature range of −50–200 °C the dielectric properties of nanocrystalline samples of BaTiO3 and BaTiO3-SiO2 (1 wt % SiO2) were studied at frequencies of 25 Hz–1 MHz. The addition of 1 wt % SiO2 to the BaTiO3 leads to a noticeable decrease in the dielectric permittivity of the material and a slight decrease in the temperatures of the ferroelectric phase transition and the transition from the orthorhombic toward tetragonal phase. It is shown that the BaTiO3-SiO2 sample exhibits some features of a relaxor ferroelectric. It is revealed that a significant contribution to the ac conductivity in the ferroelectric phase of BaTiO3 - SiO2 comes from the domain and interphase boundaries dynamics. Above TC, the hopping mechanism of conduction dominates.

Noncritical behavior in Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 relaxor ferroelectric crystals detected by acoustic emission method

[011]-oriented unpoled relaxor ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals are studied by means of acoustic emission and dielectric methods in dependence on both temperature and dc bias electric field. The rhombohedral-cubic ferroelectric phase transition and the dielectric maximum as well as the intermediate temperature are successfully detected. Both rhombohedral-cubic ferroelectric phase transition and the dielectric maximum are studied in dependence on dc bias electric field, too. No the critical end point, but the tricritical one is detected. Existence of the supercritical behavior is discussed in these crystals.

Monitoring the ferroelectric phase transition of barium titanate ceramics via impulse excitation

Impulse excitation is a suitable tool to determine the temperature dependence of Young’s modulus and to monitor the ferroelectric phase transition of unpoled barium titanate ceramics (tetragonal-to-cubic and vice versa). By measurement from room temperature to 200–300 °C and back, it is found that there is an elastic anomaly with a sharp minimum (at 120 °C during heating and 110 °C during cooling, with a completely reproducible hysteresis), below and above which Young’s modulus exhibits values of 40–50 GPa and up to 90 GPa, respectively, and damping changes abruptly from values of order 0.01 to less than 0.001.

Two new high-temperature molecular ferroelectrics [1,5-3.2.2-Hdabcn]X (X = ClO4−, ReO4−)

Molecular ferroelectrics have attracted much attention because of their excellent piezoelectricity, mechanical workability, and second harmonic effect. Here, we successfully prepared two molecular ferroelectrics [1,5–3.2.2-Hdabcn]X (X = ClO4−, 1; ReO4−, 2) by reactions of a quasi-spherical amine 1,5-diazabicycle[3.2.2]nonane (1.5–3.2.2-dabcn) with HX aqueous solution. Compounds 1 and 2 undergo high-temperature phase transitions at 381 K (1) and 396 K (2). Before and after the phase transition, they crystallize in the polar point group mm2, and the centrosymmetric point groups mmm and 4/mmm, respectively. According to Aizu rules, these two compounds experience mmmFmm2 and 4/mmmFmm2 type ferroelectric phase transitions, respectively. The ferroelectricity of both compounds is well expressed in their polycrystalline film at room temperature with low coercive voltages of 13 V for 1 and 25 V for 2. Using piezoelectric force microscopy (PFM), the 180° anti-parallel ferroelectric domains and the reversible polarization switching can be clearly observed in 1 and 2. This high-temperature molecular ferroelectric material has great application potential in flexible materials, biomechanics, intelligent wearables and other fields.

Evolving energy-storage performances during temperature-induced antiferroelectric P–R phase transition in NaNbO3-based lead-free ceramics

Temperature-driven antiferroelectric (AFE) P to AFE R phase transition in MnO2-doped 0.90NaNbO3-0.10CaTiO3 ceramics was investigated through polarization-field response, energy-storage and charge-discharge properties as well as ex/in-situ multiscale structure characterization. Both room-temperature AFE P and high-temperature AFE R phases show double polarization-electric field hysteresis loops, indicating a reversible field-driven AFE to ferroelectric (FE) phase transition. An abnormal variation of critical fields for the AFE-FE and FE-AFE phase transition and a faster polarization-field response contribute to the reduced polarization hysteresis for both AFE P and R phases but an obviously expanded linear polarization-field response only for AFE R phase, being responsible for a two-time significant enhancement in energy-storage properties from P phase to P–R phase boundary and then to R phase. The variation of unit cell anisotropy and domain morphology with temperature was found to play crucial roles in the modulated field-driven phase transition behavior and polarization-field response on heating.

The First Enantiomeric Stereogenic Sulfur-Chiral Organic Ferroelectric Crystals.

Chiral ferroelectric crystals with intriguing features have attracted great interest and many with point or axial chirality based on the stereocarbon have been successively developed in recent years. However, ferroelectric crystals with stereogenic heteroatomic chirality have never been documented so far. Here, we discover and report a pair of enantiomeric stereogenic sulfur-chiral single-component organic ferroelectric crystals, Rs-tert-butanesulfinamide (Rs-tBuSA) and Ss-tert-butanesulfinamide (Ss-tBuSA) through the deep understanding of the chemical design of molecular ferroelectric crystals. Both enantiomers adopt chiral-polar point group 2 (C2) and exhibit mirror-image relationships. They undergo high-temperature 432F2-type plastic ferroelectric phase transition around 348 K. The ferroelectricity has been well confirmed by ferroelectric hysteresis loops and domains. Polarized light microscopy records the evolution of the ferroelastic domains, according with the fact that the 432F2-type phase transition is both ferroelectric and ferroelastic. The very soft characteristics with low elastic modulus and hardness reveals their excellent mechanical flexibility. This finding indicates the first stereosulfur chiral molecular ferroelectric crystals, opening up new fertile ground for exploring molecular ferroelectric crystals with great application prospects.

The First Enantiomeric Stereogenic Sulfur‐Chiral Organic Ferroelectric Crystals

AbstractChiral ferroelectric crystals with intriguing features have attracted great interest and many with point or axial chirality based on the stereocarbon have been successively developed in recent years. However, ferroelectric crystals with stereogenic heteroatomic chirality have never been documented so far. Here, we discover and report a pair of enantiomeric stereogenic sulfur‐chiral single‐component organic ferroelectric crystals, Rs‐tert‐butanesulfinamide (Rs‐tBuSA) and Ss‐tert‐butanesulfinamide (Ss‐tBuSA) through the deep understanding of the chemical design of molecular ferroelectric crystals. Both enantiomers adopt chiral‐polar point group 2 (C2) and exhibit mirror‐image relationships. They undergo high‐temperature 432F2‐type plastic ferroelectric phase transition around 348 K. The ferroelectricity has been well confirmed by ferroelectric hysteresis loops and domains. Polarized light microscopy records the evolution of the ferroelastic domains, according with the fact that the 432F2‐type phase transition is both ferroelectric and ferroelastic. The very soft characteristics with low elastic modulus and hardness reveals their excellent mechanical flexibility. This finding indicates the first stereosulfur chiral molecular ferroelectric crystals, opening up new fertile ground for exploring molecular ferroelectric crystals with great application prospects.

Influence of domain walls and defects on the electrocaloric effect

The electrocaloric (EC) effect is the adiabatic temperature change of a material in a varying external electric field, which is promising for novel cooling devices. While the fundamental understanding of the caloric response of defect-free materials is well developed, there are important gaps in the knowledge about the reversibility and time-stability of the response. In particular, it is not settled how the time-dependent elements of microstructure that are always present in real materials act on the field-induced temperature changes. Ab initio based molecular dynamics simulations allow us to isolate and understand the effects arising from domain walls (DWs) and defect dipoles and to study their interplay. We show that DWs in cycling fields do not improve the response in either the ferroelectric (FE) phase or at the FE phase transition, but may result in irreversible heat losses. The presence of defect dipoles may be beneficial for the EC response for proper field protocols, and interestingly this benefit is not too sensitive to the defect configuration.

Proton-mediated reversible switching of metastable ferroelectric phases with low operation voltages.

The exploration of ferroelectric phase transitions enables an in-depth understanding of ferroelectric switching and promising applications in information storage. However, controllably tuning the dynamics of ferroelectric phase transitions remains challenging owing to inaccessible hidden phases. Here, using protonic gating technology, we create a series of metastable ferroelectric phases and demonstrate their reversible transitions in layered ferroelectric α-In2Se3 transistors. By varying the gate bias, protons can be incrementally injected or extracted, achieving controllable tuning of the ferroelectric α-In2Se3 protonic dynamics across the channel and obtaining numerous intermediate phases. We unexpectedly discover that the gate tuning of α-In2Se3 protonation is volatile and the created phases remain polar. Their origin, revealed by first-principles calculations, is related to the formation of metastable hydrogen-stabilized α-In2Se3 phases. Furthermore, our approach enables ultralow gate voltage switching of different phases (below 0.4 volts). This work provides a possible avenue for accessing hidden phases in ferroelectric switching.

Polymer actuation using a Joule-heating-induced ferroelectric phase transition.

Polymer actuation using a Joule-heating-induced ferroelectric phase transition.

Electro-thermal actuation in percolative ferroelectric polymer nanocomposites.

The interconversion between electrical and mechanical energies is pivotal to ferroelectrics to enable their applications in transducers, actuators and sensors. Ferroelectric polymers exhibit a giant electric-field-induced strain (>4.0%), markedly exceeding the actuation strain (≤1.7%) of piezoelectric ceramics and crystals. However, their normalized elastic energy densities remain orders of magnitude smaller than those of piezoelectric ceramics and crystals, severely limiting their practical applications in soft actuators. Here we report the use of electro-thermally induced ferroelectric phase transition in percolative ferroelectric polymer nanocomposites to achieve high strain performance in electric-field-driven actuation materials. We demonstrate a strain of over 8% and an output mechanical energy density of 11.3 J cm-3 at an electric field of 40 MV m-1 in the composite, outperforming the benchmark relaxor single-crystal ferroelectrics. This approach overcomes the trade-off between mechanical modulus and electro-strains in conventional piezoelectric polymer composites and opens up an avenue for high-performance ferroelectric actuators.

Investigation of dielectric relaxor-like anomaly behaviour of non-ferroelectric BaZrO3 polycrystalline ceramic

The dielectric responses and ac conductivity of non-ferroelectric BaZrO3 polycrystalline ceramic were examined in the wide ranges of frequency and temperature. The colossal dielectric behaviour was detected in the dielectric spectra, accompanied by two relaxor-like anomalies. The activation energy associated with the relaxor behaviour at low temperature regions was estimated to be 0.85 eV. The bulk relaxation and Maxwell-Wagner relaxation effect are responsible for the oxygen-vacancy induced pseudo-relaxor behaviour at low-temperature dielectric anomalies. The dielectric anomaly at 585 °C was confirmed to be a paraelectric to ferroelectric phase transition induced by the process of disordered to ordered state of oxygen vacancies. A modified empirical Cole-Cole model was proposed to explain the frequency-dependent permittivity and dielectric loss spectra. The two humps at low and high-temperature regions associated with oxygen-vacancy induced pseudo-relaxor and paraelectric to the ferroelectric phase transition, respectively, were observed in the temperature-dependent ac conductivity study.

Ferroelectric phase transitions in epitaxial antiferroelectric PbZrO3 thin films

The archetypical antiferroelectric, PbZrO3, is currently attracting a lot of interest, but no consensus can be clearly established on the nature of its ground state as well as on the influence of external stimuli over its physical properties. Here, the antiferroelectric state of 45-nm-thick epitaxial thin films of PbZrO3 is established by observing the characteristic structural periodicity of antiparallel dipoles at the atomic scale, combined with clear double hysteresis of the polarization-electric field response related to antiferroelectric–to–ferroelectric phase transitions. Surprisingly, while the antiferroelectric state is identified as the ground state, temperature-dependent measurements show that a transition to a ferroelectric-like state appears in a large temperature window (100 K). Atomistic simulations further confirm the existence, and provides the origin, of such ferroelectric state in the films. Electric-field-induced ferroelectric transitions are also detected by the divergence of the piezoresponse force microscopy response. Using this technique, we further reveal the signature of a ferroelectric ground state for 4-nm-thick PbZrO3 films. Compared with bulk crystals, these results suggest a more complex competition between ferroelectric and antiferroelectric phases in epitaxial thin films of PbZrO3.

Stability over time of ferroelectric phase transition and polarization switching in a nanocomposite based on potassium dihydrogen phosphate filled with cellulose

Stability over time of ferroelectric phase transition and polarization switching in a nanocomposite based on potassium dihydrogen phosphate filled with cellulose

Peculiarities of Modified Ceramics (Na0.5Bi0.5)TiO3–BaTiO3–(K0.5Na0.5)NbO3

Single-phase ceramic samples with new compositions (1 – x – у)(Na0.5Bi0.5)TiO3–хBaTiO3–у(K0.5Na0.5)NbO3 (x = 0.05, у = 0–0.15) modified with ZnO and GeO2 additions were obtained by solid-phase synthesis. Their crystal structure, microstructure, and dielectric and local piezoelectric properties were studied. A phase with a perovskite structure with a pseudocubic unit cell was found to form in all of the synthesized samples; it was shown that the unit cell volume increased as a result of the partial replacement of base cations by complex additive cations. The ferroelectric phase transitions were confirmed by dielectric spectroscopy. Residual piezoelectric hysteresis loops were obtained for the synthesized samples in the polarization switching spectroscopy mode, which confirmed the switching of ferroelectric polarization.

Pressure‐driven phase transition and energy conversion in ferroelectrics: Principles, materials, and applications

AbstractThe pressure‐driven explosive energy‐conversion (EEC) effect of ferroelectric (FE) materials has been extensively studied in scientific research and high‐tech applications owing to its high pulse‐power output capability. The fundamental principle of this effect is pressure‐driven phase transition and depolarization in FE materials, accompanied by discharging behavior from the charge release upon pressure loading. Pb(Zr,Ti)O3has been an excellent example of a materials exhibiting these properties. However, recent investigations have been focused on developing other lead‐based or lead‐free materials with a higher energy‐storage ability and better temperature stability. In this article, we review the recent progress achieved in the past decades on different types of lead‐based and lead‐free ceramics, single crystals, and multilayer films, based on their unique pressure‐driven phase transition and energy‐conversion properties. Their pulse power discharging performance under actual shock‐wave compression is also summarized, followed by a detailed discussion of the failure mechanism under shock‐wave compression. Finally, several issues and perspectives are proposed for future investigation in this area. All these not only assist in the design of new materials for high‐performance EEC but are also helpful for the practical application of these promising materials in pulse‐power technologies.

Structure, morphological and dielectric properties of BZT-BST ceramics

Barium zirconate titanate (BZT), a relaxor ferroelectric ceramic based on barium titanate (BT), has received substantial research. In this study, Ba(Zr0.2Ti0.8)O3 and Ba0.85Sr0.15TiO3 were separately prepared by solid state method and thereafter they were mixed in the following ratio (1-x){Ba(Zr0.2Ti0.8)O3} – x{Ba0.85Sr0.15TiO3} (x = 0, 0.1, 0.2) (BZT-BST) to make ceramic composite using high energy ball mill. The structure, morphology, and dielectric properties of these composites have been systematically studied. The crystal structure of the BZT-BST composite was determined by X-ray diffraction technique. The XRD pattern shows a well-developed tetragonal perovskite crystal structure. Without a second phase, all samples exhibit the perovskite structured BZT diffraction peaks. Permittivity measurements show that the relative permittivity (εr) of the composite increases as the amount of BST increases from × = 0 to × = 0.1, but then decreases at × = 0.2, indicating a broad transition in dielectric constant. The observed Curie temperatures (Tc) for all the compositions mentioned are 31 °C, 36 °C, and 43 °C, of ​​which the dielectric maximum for each composition is found to be ∼ 5000, 6100, and 3810 at the frequency of 1 kHz. It can be seen that the relative permittivity (εr) of all three BZT-BST compositions decreases gradually with increasing frequency. At low frequency, there are several different polarizations mechanisms. However, at high frequencies, only electronic displacement polarization exists. Morphological analysis of the sintered samples by Field emission scanning electron microscopy (FESEM) shows that the pure BZT ceramics have numerous pores. The compactness of BZT-BST ceramics was significantly enhanced by the addition of BST. The grain size of BZT-BST ceramics increases with increasing BST content. Pure BZT ceramics exhibit ferroelectric diffusion phase transition characteristics with weak relaxation behaviour. BZT-BST composites exhibit increasing relaxation behaviour with increasing BST content. These may be the most promising candidate materials for capacitor applications.

Giant dynamic electromechanical response via field driven pseudo-ergodicity in nonergodic relaxors

Enhanced electromechanical response can commonly be found during the crossover from normal to relaxor ferroelectric state, making relaxors to be potential candidates for actuators. In this work, (Pb0.917La0.083)(Zr0.65Ti0.35)0.97925O3 ceramic was taken as a case study, which shows a critical nonergodic state with both double-like P-E loop and irreversible relaxor-normal ferroelectric phase after poling at room temperature. The low-hysteresis linear-like S-P2 loop, in-situ synchrotron X-ray diffraction and transmission electron microscope results suggest that the nonpolar relaxor state acts as a bridge during polarization reorientation process, accompanying which lattice strain contributes to 61.8% of the total strain. In other words, the transformation from normal ferroelectric to nonergodic relaxor state could be triggered by electric field through polarization contraction, which could change to be spontaneously with slightly increasing temperature in the nonergodic relaxor zone. Therefore, pseudo-ergodicity in nonergodic relaxors (i.e. reversible nonergodic-normal ferroelectric phase transition) driven by periodic electric field should be the main mechanism for obtaining large electrostrain close to the nonergodic-ergodic relaxor boundary. This work provides new insights into polarization reorientation process in relaxor ferroelectrics, especially phase instability in nonergodic relaxor zone approaching to freezing temperature.

Charged Domain Walls in BaTiO3 Crystals Emerging from Superdomain Boundaries

AbstractPrevious experiments with barium titanate crystals have shown that electric field applied in the vicinity of its ferroelectric phase transition can be used to introduce peculiar ferroelectric domain walls, persisting to the ambient conditions: head‐to‐head charged walls compensated by the 2D electron gas. The present in situ optical observations allow the documentation of the early stage of this poling process in which the cubic and ferroelectric phases coexist, the latter being broken into multiple martensitic superdomains, separated by superdomain boundaries. It is revealed that the transient superdomains are subsequently converted into the regular ferroelectric domains, while the superdomain boundaries transform into the desired charged domain walls. In order to assign the observed transient domain patterns, to understand the shapes of the observed ferrolectric precipitates and their agglomerates as well as to provide the overall interpretation of the recorded domain formation process, the implications of the mechanical compatibility of the coexisting superdomain states are derived in the framework of the Wechsler–Lieberman–Read theory. These results also suggest that both the electric conductivity and interlinked motion of the superdomain boundaries and phase fronts are involved in the transport of the compensating charge carriers toward the charged domain wall location.

Nanoscale investigation on electric field induced ferroelectric phase transitions in the rhombohedral PMN-PT single crystal

The excellent piezoelectric property of Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT) single crystals has attracted increasing attentions for their application in electromechanical devices. Generally, the electric field induced phase transition is an important contribution to the piezoelectric response. Understanding the pathway of electric field induced phase transition is essential for the practical application of PMN-PT crystals. Here, evolution of the domain structure and surface screening charges during phase transitions in the (001) oriented 0.72PMN-0.28PT crystal were studied at nanoscale via piezo-response force microscopy (PFM) and Kelvin probe force microscopy (KPFM). In combination with confocal polarized Raman spectroscopy, electric field induced phase transitions were locally studied. PFM tip bias poling in 0.72PMN-0.28PT single crystal results in a rhombohedral to monoclinic phase transition. And the monoclinic phase relaxes back to the rhombohedral at elevated temperatures. Our work provides nanoscale investigations on the electric field induced phase transition, and will be instructive for the practical application of PMN-PT single crystals.