Paraelectric-antiferroelectric Phase Transition Research Articles

Static and dynamic strain relaxation associated with the paraelectric-antiferroelectric phase transition in PbZrO3

Order parameter coupling associated with the first order, improper ferroelastic (Pm3̅m - Pbam) transition at ~510 K in PbZrO3 has been analysed from the perspective of strain and elasticity. Formal treatment of spontaneous strains using lattice parameter data from the literature reveals typical coupling with the order parameter for octahedral tilting, Q R, and stronger coupling with the order parameter for antiferroelectric displacements,Q Σ. These indicate that coupling between the two order parameters via common strains is not only biquadratic, λQ 2RQ 2Σ, but may also have contributions from a higher order term, λQ 2RQ 4Σ. Variations of elastic and anelastic properties obtained by resonant ultrasound spectroscopy (RUS) at frequencies in the vicinity of 1 MHz show softening as the transition point is approached from above, discontinuous stiffening at the transition point and a pattern of further stiffening in the stability field of the orthorhombic structure. Below the transition point, the pattern of stiffening resembles the evolution of Q 2R and Q 2Σ, as is typical of coupling dominated by terms with the form λe2Q 2, where e is a spontaneous shear strain. The absence of softening due to terms of the form λeQ 2 implies that the relaxation time for changes in the order parameters in response to an induced shear strain is slower than ~10-6 s. Also in contrast with measurements from the literature made at lower frequencies, no evidence for mobility of ferroelastic domain walls was observed at RUS frequencies. A peak in acoustic loss observed at the transition point and precursor softening in the stability field of the cubic phase are consistent with evidence for local dynamical polar clusters. Apart from some differences in relaxation times, the antiferroelectric transition in PbZrO3 does not appear to be overtly different from ferroelectric transitions such as occur in BaTiO3.

Room‐Temperature Symmetric Giant Positive and Negative Electrocaloric Effect in PbMg0.5W0.5O3 Antiferroelectric Ceramic

AbstractAs an emerging solid‐state refrigeration technology with zero‐emission and high energy conversion efficiency, there is a compelling need for ferroelectric materials with giant electrocaloric effects (ECEs) at room temperature suitable for refrigeration applications. The complex perovskite antiferroelectric (AFE), PbMg0.5W0.5O3, containing non‐equivalent B‐site ions with a symmetric giant positive and negative ECE near room temperature is presented. At the Curie temperature of 36 °C, the first‐order AFE–paraelectric phase transition gives rise to a large enthalpy change of 3.92 J g−1, more than four times that of BaTiO3. This leads to a significant ECE under the influence of an electric field. The direct electrocaloric characterization shows that the adiabatic temperature change, ΔT, exhibits symmetric peaks with a giant positive maximum of 1.79 K (ΔS = 1.68 J kg−1 K−1) at 36 °C and a negative maximum of −2.02 K (ΔS = −1.93 J kg−1 K−1) at 34 °C. The ultrahigh magnitude of ΔT near room temperature makes PbMg0.5W0.5O3 a superior electrocaloric material far beyond traditional PbZrO3‐based AFEs. The coexistence of symmetric giant positive and negative ΔT to further improve cooling efficiency is expected. In addition, the good reversibility and negligible leakage current should pave the way for practical applications.

Origin of large negative electrocaloric effect in antiferroelectric PbZrO3

We have studied the electrocaloric response of the archetypal antiferroelectric $\mathrm{PbZr}{\mathrm{O}}_{3}$ as a function of voltage and temperature in the vicinity of its antiferroelectric-paraelectric phase transition. Large electrocaloric effects of opposite signs, ranging from an electrocooling of \ensuremath{-}3.5 K to an electroheating of $+5.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, were directly measured with an infrared camera. We show by calorimetric and electromechanical measurements that the large negative electrocaloric effect comes from an endothermic antiferroelectric-ferroelectric switching, in contrast to dipole destabilization of the antiparallel lattice, previously proposed as an explanation for the negative electrocaloric effect of antiferroelectrics.

Dielectric dispersion and ac conductivity behavior in tin-modified lead zirconate antiferroelectric single crystals

Frequency and temperature dielectric response and electrical conductivity behavior around the antiferroelectric–paraelectric phase transition temperature were studied in PbZr0.93Sn0.07O3 antiferroelectric single crystals. The contribution of conductive processes to dielectric relaxation for the studied frequency range is discussed, considering oxygen vacancies and electronic transport. The relaxation processes below the transition temperature are associated with short-range polaronic hopping due to the interaction of the charge carriers (trapped electrons) with the distorted crystal lattice. Based on the specific coupling between electrons and phonons in the largely distorted oxygen octahedral sublattice of PbZr1−xSnxO3 crystals, an attempt to explain the formation of the incommensurate phase was undertaken.

Paraelectric-Antiferroelectric Phase Transition and Capacitance Enhancement by as-Deposited TiN Capping on ZrO <sub>2</sub>

Paraelectric-Antiferroelectric Phase Transition and Capacitance Enhancement by as-Deposited TiN Capping on ZrO <sub>2</sub>

Interlayer strain effects on the structural behavior of BiFeO3/LaFeO3 superlattices

Artificial (BiFeO3)0.5Λ/(LaFeO3)0.5Λ superlattices have been grown by pulsed laser deposition. The periodicity Λ was varied from 150 Å to 25 Å and the relative ratio between BiFeO3 (BFO) and LaFeO3 (LFO) is kept constant in each period. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy investigations indicate antiferroelectric-like structures for large periodicity (Λ ≥ 76 Å), while Pnma LaFeO3-like structures are observed for small periodicity Λ ≤ 50 Å. Room temperature magnetic measurements were obtained by vibrating sample magnetometry and suggest antiferromagnetic ordering with weak ferromagnetism. Temperature dependent x-ray diffraction studies show an important shift of paraelectric-antiferroelectric phase transition scaling with BFO thickness. Strain and size effects explain this behavior and discussion is also made on the possible role of the oxygen octahedral rotation/tilt degree of freedom.

Successive Phase Transition, Dielectric Ordering, and Liquid Crystalline Behavior of Simple (Laurylammonium)(Phenyl Phosphates) Salts.

Successive phase transitions of three kinds of simple 1:1 organic salts of laurylammonium (LA)-phenyl (3-pyridyl) phosphate derivative were examined in terms of thermal properties, single crystal X-ray structural analyses, powder X-ray diffractions, and dielectric responses, where the phosphate anion was chemically modified from phenylphosphate (1) and 3-pyridylphosphate (2) to m-fluorophosphate (3). All 1:1 simple organic salts showed the successive solid-solid and solid-smectic A (SmA) phase transition with high thermal stability. Isostructural alternate cation-anion layer was observed in LA-1 and LA-2, and the packing structure of LA-3 was different from those of the former salts. The L-shaped cation-anion conformation in the molecular assemblies was transformed to the rod-like conformation through the phase transition to SmA phase, where both conformations coexisted in the intermediate solid phase of LA-2 and LA-3. The DSC, PXRD, and dielectric responses of LA-2 showed the antiferroelectric-paraelectric phase transition couple with the flip-flop motion of 3-pyridyl ring along the long axis of the molecule. On the contrary, such molecular motion of the phenyl ring did not show the dielectric phase transition due to no dipole change during molecular rotation of phenyl ring. The motional freedom of m-fluorophenyl ring in LA-3 was completely suppressed by the steric hindrance from the neighboring anions in the absence of dielectric ordering.

Collective In-Plane Molecular Rotator Based on Dibromoiodomesitylene π-Stacks.

Interest in artificial solid-state molecular rotator systems is growing as they enable systems to be designed for achieving specific physical functions. The phase transition behavior of four halomesitylene crystals indicated dynamic in-plane molecular rotator characteristics in dibromoiodomesitylene, tribromomesitylene, and dibromomesitylene crystals. Such molecular rotation in diiodomesitylene crystals was suppressed by effective I···I intermolecular interactions. The in-plane molecular rotation accompanied by a change in dipole moment resulted in dielectric phase transitions in polar dibromoiodomesitylene and dibromomesitylene crystals. No dielectric anomaly was observed for the in-plane molecular rotation of tribromomesitylene in the absence of this dipole moment change. Typical antiferroelectric-paraelectric phase transitions were observed in the dibromomesitylene crystal, whereas the dielectric anomaly of dibromoiodomesitylene crystals was associated with the collective in-plane molecular rotation of polar π-molecules in the π-stack. We found that the single-rope-like collective in-plane molecular rotator was dominated by intermolecular I···I interactions along the π-stacking column of polar dibromoiodomesitylene.

Structural evolution and enhanced magnetization of Bi1−xPrxFeO3

The structural, ferroelectric, vibrational, and magnetic properties of polycrystalline Bi1−xPrxFeO3 (0≤x≤0.50) powders are investigated by the measurements of X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering spectroscopy, and magnetization at room temperature. Our results reveal that the rare-earth ion Pr substitution at Bi site causes the structural transformations from rhombohedral R3c phase to orthorhombic Pbam phase at x≈0.15, and then to orthorhombic Pnma phase at higher Pr concentration x≈0.25, accompanying the ferroelectric–antiferroelectric–paraelectric phase transition. Measurements of magnetic properties confirm that Pr substitution can improve the magnetization of BiFeO3 before approaching the first phase transition. We find that an inverse behavior occurs after passing a maximum across the antiferroelectric–paraelectric phase boundary. We also obtain the unique switching behavior in low magnetic field of Bi0.5Pr0.5FeO3 from the field dependence on magnetization, indicating the existence of the antiferromagnetic ordering.

Ferroelectric and antiferroelectric properties of Si-doped HfO2 thin films

Ferroelectric and antiferroelectric HfO2 nano-films were prepared by changing silicon doping concentration, and their basic properties conpared in terms of polarization hysteresis, capacitance-voltage and leakage-voltage behavior, as well as the effect of temperature on phase stability. Antiferroelectric thin film exhibits a higher dielectric constant than the ferroelectric film, and is characterized by the double polarization hysteresis loops due to reversible antiferroelectric-ferroelectric phase transition induced during loading and unloading processes of electric field. No antiferroelectric-paraelectric phase transition is observed at measuring temperatures up to 185 ℃. The negative differential resistivity effect observed in leakage measurements is attributed to the contributions from slow response mechanisms like polarization relaxation.

Study of Dielectric Properties and Phase Transformation of Thermally Modified Nano-Composite PbIn1/2Nb1/2O3

Differential thermal analysis as well as Raman and dielectric studies of PbIn1/2Nb1/2O3 single crystals exhibiting a different degree of order were performed. For this purpose two ordering procedures were applied. In Procedure A the as grown crystals were annealed at 650°C for different periods of time. Whereas in Procedure B the crystals were annealed at various temperatures, ranging from 650 to 850°C, long enough to reach the thermodynamic equilibrium state. With the increase of the degree of order, the heat anomaly related to the antiferroelectric-paraelectric phase transitions in the ordered regions, increase and shifts towards higher temperatures. Simultaneously the diffuse and frequency dependent maximum of the dielectric permittivitty ϵ(T), characteristic for disordered crystals, gradually forms a sharp maximum typical for ordered crystals and shifts towards higher temperatures. The evolution of Raman spectra at room temperature also indicates their sensitivity to the ordering state. Systematic dielectric investigations allowed us to distinguish two contributions to the dielectric response, one originating from the antiferroelectric and other from the ferroelectric nano-regions. The diagrams showing temperatures of the observed phase transitions versus annealing conditions as well as the coexistence of different phases are given in the paper. The experiments performed showed that lead indium niobate presents a thermally modified nano-composite structure composed of ordered antiferroelectric regions embedded in a disordered ferroelectric matrix.

Ti‐Doping to Reduce Conductivity in Bi0.85Nd0.15FeO3 Ceramics

AbstractIn 2009, Karimi et al. reported that Bi1‐xNdxFeO3 0.15 ≤ x ≤ 0.25 exhibited a PbZrO3 (PZ)‐like structure. These authors presented some preliminary electrical data for the PZ‐like composition but noted that the conductivity was too high to obtain radio‐frequency measurements representative of the intrinsic properties. In this study, Bi0.85Nd0.15Fe1‐yTiyO3 (0 ≤ y ≤ 0.1) were investigated, in which Ti acted as a donor dopant on the B‐site. In contrast to the original study of Karimi et al., X‐ray diffraction (XRD) of Bi0.85Nd0.15FeO3 revealed peaks which were attributed to a mixture of PZ‐like and rhombohedral structures. However, as the Ti (0 < y ≤ 0.05) concentration increased, the rhombohedral peaks disappeared and all intensities were attributed to the PZ‐like phase. For y = 0.1, broad XRD peaks indicated a significant decrease in effective diffracting volume. Electron diffraction confirmed that the PZ‐like phase was dominant for y ≤ 0.05, but for y = 0.1, an incommensurate structure was present, consistent with the broadened XRD peaks. The substitution of Fe3+ by Ti4+ decreased the dielectric loss at room temperature from >0.3 to <0.04 for all doped compositions, with a minimum (0.015) observed for y = 0.03. The decrease in dielectric loss was accompanied by a decrease in the room temperature bulk conductivity from ∼1 mS cm−1 to <1 μS cm−1 and an increase in bulk activation energy from 0.29 to >1 eV. Plots of permittivity (ϵr) versus temperature for 0.01 ≤ y ≤ 0.05 revealed a step rather than a peak in ϵr on heating at the same temperature determined for the antiferroelectric–paraelectric phase transition by differential scanning calorimetry. Finally, large electric fields were applied to all doped samples which resulted in a linear dependence of polarisation on the electric field similar to that obtained for PbZrO3 ceramics under equivalent experimental conditions.

Growth and orientation dependence of electrical properties of 0.92Na0.5Bi0.5TiO3-0.08 K0.5Bi0.5TiO3 lead-free piezoelectric single crystal

A 0.92Na0.5Bi0.5TiO3-0.08 K0.5Bi0.5TiO3 (0.92NBT-0.08KBT) lead-free piezoelectric single crystal with dimensions of Φ 35 × 10 mm was successfully grown by the top-seeded solution growth method. The effective segregation coefficient for K was calculated to be 0.27. An x-ray powder diffraction measurement showed that the as-grown crystal possesses a rhombohedral perovskite structure at room temperature. The room-temperature dielectric constants for poled 〈001〉, 〈110〉, and 〈111〉 oriented crystal samples are found to be 683, 567, and 435 at 1 kHz, respectively. The (Tm, ɛm) values for 〈001〉, 〈110〉, and 〈111〉 oriented crystals are (316 °C, 4318), (317 °C, 4160), and (318 °C, 4348) at 1 kHz, which indicate that the dielectric parameters of the as-grown crystals show weaker anisotropy. The curves, ɛ(T), for the three crystallographic orientations show two anomalies at about 170 and 320 °C, respectively, relating to the ferroelectric-antiferroelectric phase and the antiferroelectric-paraelectric phase. There is a thermal hysteresis, ΔT ≈ 35 °C for the ferroelectric-antiferroelectric phase transformation between heating and cooling. The antiferroelectric phase, the thermal hysteresis, and the dielectric relaxor behavior around 170 °C can be attributed to the formation of an intermediate orthorhombic modulated phase at 170–320 °C. For the 〈001〉, 〈110〉, and 〈111〉 crystal samples, the room-temperature piezoelectric constants, d33, reach 175, 130, and 70 pC/N, respectively. The remanent polarization for the 〈001〉, 〈110〉, and 〈111〉 crystal samples are 8.1, 10.8, and 13.5 μC/cm2, respectively, and the ratio is 1:1.33:1.67, close to 1:2:3. The diffusive factors, α, are found to be 1.94, 1.91, and 1.50 for the 〈001〉, 〈110〉, and 〈111〉 oriented crystal samples, which indicate that the antiferroelectric-paraelectric phase transition of the as-grown 0.92NBT-0.08KBT crystal is a strong diffuse one. The electromechanical coupling coefficients for the 〈001〉, 〈110〉, and 〈111〉 oriented 0.92NBT-0.08KBT crystals at room temperature are 52, 50, and 48%, respectively. The values of kt for the three main crystallographic orientations change slightly with the increase of temperature from 15 to 140 °C, demonstrating a relatively stable thermal electromechanical coupling property.

Heat capacity at constant pressure and thermodynamic properties of phase transitions in PbMO3 (M=Ti, Zr and Hf)

The heat capacity of PbMO3 (M=Ti, Zr and Hf) at constant pressure was measured using a differential scanning calorimeter (DSC) from room temperature up to 870 K. Large anomalies were found in the heat capacity curves, corresponding to the ferroelectricparaelectric phase transition in PbTiO3 (PT), the antiferroelectric-paraelectric phase transitions in PbZrO3 (PZ) and PbHfO3 (PH). The transition entropies were estimated as 7.3 J K−1 mol−1 (PT), 9.9 J K−1 mol−1 (PZ) and 9.3 J K−1 mol−1 (PH). These values of transition entropies are much larger than that of a typical displacive-type phase transition.

Reinvestigation of Phase Transitions in Na0.5Bi0.5TiO3 by TEM. Part II: Second Order Orthorhombic to Tetragonal Phase Transition

NBT presents an orthorhombic to tetragonal second order phase transition that occurs near 320 °C. It corresponds to the so-called antiferroelectric-paraelectric phase transition. A model is presented in which the diffuse phase transition is achieved by the progressive canceling of the antiphase octahedra tilting prevailing within a - b + a - orthorhombic structure, whereas the in-phase tilting is maintained. This transformation gives finally rise to the a 0 a 0 c + octahedra tilting system of the tetragonal phase. Electron diffraction experiments show that a long-range ordering occurs within the tetragonal phase. It probably develops as P4 2 /mnm ordered nanoregions disseminated within a P4-/mbm disordered matrix. The order is still visible in the temperature domain of the cubic phase.

Crystallographic and dielectric properties of flux grown [formula omitted] (B′B″: InNb, InTa, YbNb, YbTa and MgW) single crystals

Single crystals of PbIn 1/2Nb 1/2O 3 (PIN), PbIn 1/2Ta 1/2O 3 (PIT), PbYb 1/2Nb 1/2O 3 (PYN), PbYb 1/2Ta 1/2O 3 (PYT) and PbMg 1/2W 1/2O 3 (PMW) have been grown by the flux method. The PbO-based solvents were used. Transparent, light yellow and arrow like shaped PIN and PIT crystals of the perovskite structure were obtained. Small amounts of red and of octahedron habit PIN and PIT crystals of the pyrochlore type were simultaneously grown. In the case of PYN, PYT and PMW only the crystals of the perovskite structure have been grown. The transparent and brown PYN and PYT crystals of octahedron habit were obtained. The transparent, light yellow and of octahedron or truncated octahedron shape PMW crystals were grown. The crystals were characterised by X-ray and dielectric studies. They showed that as-grown PIN crystals are nearly disordered, exhibit the rhombohedral distortion of the pseudo-perovskite unit cell and reveal relaxor behaviour. The partially ordered PIT crystals show monoclinic distortion and undergo antiferroelectric–paraelectric phase transition. The PYN, PYT and PMW single crystals, characterised by chemical order in the B′/B″ ion sublattice, exhibit orthorhombic symmetry and undergo the first-order antiferroelectric–paraelectric phase transitions.

Investigation on the Symmetry and the Order Parameter of the Displacive Antiferroelectric Phase Transition

The shortage of the order parameter of the antiferroelectric phase in the previous reference is pointed out. An axial vector R = ∑ iqi ri × Δ ri/V was proposed as the order parameter of the displacive antiferroelectric phase. This vector is of the symmetry groupC ∞ i . Using R as the order parameter, we reinvestigated the antiferroelectric model of Kittle type. We find that the vector can adequately reflect the symmetry change of the paraelectric-antiferroelectric phase transition by using Curie principle.

Very High Resolution 17O NMR Evidence for Displacive Behavior in Hydrogen-Bonded Solids: Squaric Acid

Magic angle sample spinning (MAS)7O NMR studies of the paraelectric-antiferroelectric phase transition (at TC = 373 K) of the model hydrogen-bonded compound squaric acid (H2C4O4 ) reveal a significant displacive component in the microscopic mechanism of the transition. The high resolution (400% enhancement over conventional MAS) was obtained by utilizing single crystals. All four oxygens were clearly shown to be chemically different at T < TC . The peak assignment was supported by quantum theoretical calculations of the 17O isotropic chemical shifts using a pentamer model of the crystal structure. There was a clear break in the isotropic part of the chemical shift on lowering the temperature through TC , implying that the phase transition involves a distortion of the whole H2C4O4 framework, and not just the order-disorder rearrangement of the H's i.e., future models of the transition should include a displacive component, in addition to an order-disorder part. The observation of the double at T > TC implies that the two O─H⋅⋅⋅O chains retain their difference in the paraelectric phase as well. This is consistent with the one-dimensional Ising chain model, in contrast to the more prevalent, two-dimensional, C4O4 square-lattice model.

Phase transition and dielectric properties of La-doped Pb(Zr,Sn,Ti)O3 antiferroelectric ceramics under hydrostatic pressure and temperature

Phase transition and dielectric properties of La-doped Pb(Zr,Sn,Ti)O3 antiferroelectric ceramics under hydrostatic pressure and temperature have been studied, and effects of temperature on the pressure-induced phase transition and the dielectric property dependence on the applied hydrostatic pressure have been investigated. It has been found from experimental results that the ferroelectric–antiferroelectric phase transition pressure is decreased with increasing temperature, and that when applying hydrostatic pressure the ferroelectric–antiferroelectric phase transition temperature is decreased and antiferroelectric–paraelectric phase transition temperature is increased. All these observed phenomena are very useful and informative for deep understanding of the behaviors of temperature and pressure-induced dielectric frequency dispersion and diffuse phase transition.

Thermal Behavior and Phase Transition in PZT near the Morphotropic Phase Boundary

The heat capacities of single crystals of antiferroelectric PbZrO 3 and PbZr 0.99 Ti 0.01 O 3 , and sol-gel derived ceramics of ferroelectric PbZr 1 m x Ti x O 3 ( x = 0.46, 0.48, and 0.50) were measured by a.c. calorimetry. Only one sharp anomaly at 505.6 K in a PbZrO 3 single crystal showed the paraelectric-antiferroelectric phase transition without any accompanying intermediate phase. In addition to the antiferroelectric phase transition, PbZr 0.99 Ti 0.01 O 3 showed two clear anomalies that corresponded to a series of phase transitions. PZT near the morphotropic phase boundary (MPB) showed one peak and additional broad shoulder-type anomalies in C p at high temperatures. The broad shoulder showed very wide thermal hysteresis of about 140 K, which evidence suggests an intermediate state between paraelectric and ferroelectric phases. The monoclinic phase in the low-temperature region reported by Noheda et al. was confirmed.