Paraelectric Region Research Articles

Phase transition and polar cluster behavior above Curie temperature in ferroelectric BaTi0.8Zr0.2O3

We study the phase transition behavior of the ferroelectric BaTi0.8Zr0.2O3 in the paraelectric region. The temperature dependencies of thermal, polar, elastic, and dielectric properties indicate the presence of local structures above the paraelectric–ferroelectric transition temperature Tc = 292 K. The non-zero remnant polarization is measured up to a characteristic temperature T* ∼ 350 K, which coincides with the temperature where the dielectric constant deviates from the Curie–Weiss law. Resonant piezoelectric spectroscopy shows that DC field cooling above Tc using fields smaller than the coercive field leads to an elastic response and remnant piezoelectricity below T*, which likely corresponds to the coherence temperature associated with polar nanostructures in ferroelectrics. The observed remnant effect is attributed to the reorientation of polar nanostructures above Tc.

Reversible evolution of ferroelectric-antiferroelectric phase transition in lanthanum-modified NaNbO3-based ceramics

Sodium niobate (NN) lead-free perovskites have been concentrated on due to high performance and abundant phase structure. The complex structure evolution has become a hot topic of research for this kind of materials. In this work, antiferroelectric phase is recovered by introducing La3+ dopant from modified ferroelectric states, indicating reversible composition-induced antiferroelectric-ferroelectric (AFE-FE) phase transition in NN-based ceramics. Significantly, change tendency of decreasing first and then increasing appears for phase transition temperature with increasing La3+, which is different from general phenomenon for ions dopant. Antiferroelectric orthorhombic (Pbma) is induced from ferroelectric tetragonal (P4mm) with a transient state of paraelectric cubic (Pm3m) via enhancing La3+. Further, substitution on A-site and A/B-sites are revealed with low and high content of La3+, respectively, accompanied by decreased first and then increased oxygen vacancy. Moreover, obviously deteriorated piezoelectric response is observed along with poor domain switching due to the vanishing ferroelectric domain for FE-PE-AFE phase transition. Meanwhile, weak strain, piezoelectric and dielectric properties are observed for antiferroelectric phase with antiparallel dipoles, while enhanced strain and dielectric permittivity are gained around ferroelectric-paraelectric coexistence or paraelectric region originating from electric field-induced ferroelectric state from polar nanoregions. Thus, this work demonstrated an abnormal phase transition in NN-based ceramics, promoting the understanding of antiferroelectrics.

Structures and velocities of noisy ferroelectric domain walls

Ferroelectric domain wall motion is fundamental to the switching properties of ferroelectric devices and is influenced by a wide range of factors including spatial disorder within the material and thermal noise. We build a Landau-Ginzburg-Devonshire (LGD) model of ${180}^{\ensuremath{\circ}}$ ferroelectric domain wall motion that explicitly takes into account the presence of both spatial disorder and thermal noise. We demonstrate both creep flow and linear flow regimes of the domain wall dynamics by solving the LGD equations in a Galilean frame moving with the wall velocity $v$. Thermal noise plays a key role in the wall depinning process at small fields $E$. We study the scaling of the velocity $v$ with the applied DC electric field $E$ and show that noise and spatial disorder strongly affect domain wall velocities. We also show that domain walls develop a local, metastable paraelectric region and widen significantly in the presence of thermal noise in materials with ``multiwell'' potentials, representative of ferroelectrics at temperatures $T$ just below a first-order phase transition (Curie) temperature ${T}_{c}$. These calculations point to the potential of noise and disorder to become control factors for the switching properties of ferroelectric materials, for example for advancement of microelectronic applications.

Temperature-dependent ferroelastic behaviour of antiferroelectric AgNbO3

The macroscopic ferroelastic response of polycrystalline AgNbO3 was investigated under the uniaxial compressive stress of up to -300 MPa from -150 °C to 450 °C, covering weak ferroelectric, antiferroelectric, and paraelectric phase regions. It is found that AgNbO3 exhibits ferroelasticity in the weak ferroelectric (M1), antiferroelectric (M2, M3), as well as the paraelectric regions (O and T), i.e. displaying ferroelastic hysteresis and remnant strain. The changes in mechanical parameters such as coercive stress, back switching strain, and remnant strain values reflect the specific crystal symmetry features at different phase regions together with the influence of temperature on domain wall motion. With stress removed and cooled down to room temperature, X-ray diffraction showed that the sample (at M1 state) exhibited different degrees of remnant domain textures and lattice strains, depending on its phase state when being compressed. Additionally, in situ stress- and temperature-dependent Raman spectroscopy measurements revealed that uniaxial compressive stress could induce changes in NbO6 octahedra and cation displacement, especially for high-temperature phases. Overall, the ferroelasticity, effects of stress on the structure and phase transitions offer opportunities for property engineering of AgNbO3 in capacitor applications.

Effect of donor and acceptor dopants on the microstructure and dielectric properties of barium titanate based ceramics

This paper examined the microstructural and dielectric characteristics of BaTiO3 - based ceramics of the general formula BaTi1-x-yNbxMnyO3. The concentration of Mn as acceptor was variable 0.01 and 0.05 at%, while the donor (Nb) was fixed at 0.5 at%. The starting ceramic powders were produced by a conventional solid-state reaction method and sintered at 1290 and 1320oC. In BaTiO3 ceramics doped with a higher Mn concentration (0.05 at% Mn) at a sintering temperature of 1290?C, a bimodal structure with a grain of 10-30 ?m, and 1-5 ?m, was obtained. Sintering at a higher temperature (Tsin = 1320?C), regardless of Mn content, provides the achievement of a uniform microstructure with grains under than 6 ?m. The ceramics doped with 0.01 at% Mn and sintered at 1320?C are characterized by high values of the dielectric constant at room temperature and notable changes in the dielectric constant with temperature. Nb-0.05Mn BaTiO3 doped ceramics sintered at 1290?C show lower dielectric constant values due to the presence of Mn-enriched areas representing paraelectric regions. Areas richer in Mn are associated with the fine-grained structure. The dielectric constant in the investigated systems achieves a constant value for frequencies higher than 3kHz. The Curie temperature of all samples was shifted to lower values in relation to undoped BaTiO3 ceramics. According to Curie-Weiss law were determined the Curie constant C and the Curie temperature Tc.

Temperature Dependence of Dielectric Properties of Ferroelectric Heterostructures with Domain-Provided Negative Capacitance

It is well known that the ferroelectric layers in dielectric/ferroelectric/dielectric heterostructures harbor polarization domains resulting in the negative capacitance crucial for manufacturing energy-efficient field-effect transistors. However, the temperature behavior of the characteristic dielectric properties, and, hence, the corresponding behavior of the negative capacitance, are still poorly understood, restraining the technological progress thereof. Here we investigate the temperature-dependent properties of domain structures in the SrTiO3/PbTiO3/SrTiO3 heterostructures and demonstrate that the temperature–thickness phase diagram of the system includes the ferroelectric and paraelectric regions, which exhibit different responses to the applied electric field. Using phase-field modeling and analytical calculations we find the temperature dependence of the dielectric constant of ferroelectric layers and identify the regions of the phase diagram wherein the system demonstrates negative capacitance. We further discuss the optimal routes for implementing negative capacitance in energy-efficient ferroelectric field-effect transistors.

Role of charge compensation mechanism and defect dipoles on properties of Mn doped BCT ceramics

Single-phase Mn doped Barium Calcium Titanate (BCT) (Ba0.80Ca0.20Ti1-xMnxO3; x = 0.000, 0.005, 0.010, 0.015 and 0.020) lead free ceramics have been prepared by conventional solid-state reaction method. XRD studies and Rietveld refinement confirmed the existence of tetragonal phase (P4mm) for all prepared ceramic compositions. The average grain size increased up to x = 0.005 and thereafter it decreased with increase in Mn content in BCT compositions. Analysis of temperature-dependent dielectric study revealed phase transformation from tetragonal to cubic phase and defect dipole induced anomaly in paraelectric region of temperature-dependent dielectric constant (εʹ–T) curve. Degree of diffusiveness increased with Mn doping in BCT ceramics as confirmed by evaluating diffused phase transition (DPT) parameters (γ and δc) by Power Law fitting and width of diffused phase transition (Dʹ) obtained from derivative of εʹ–T curve. Ferroelectric (P-E loops) study revealed that ceramic composition with x = 0.015 Mn content showed the highest remnant polarization (Pr) and maximum polarization (Pmax) of 14.10 μC/cm2 and 24.20 μC/cm2 respectively. Enhancement in energy storage properties with applied electric fields have been observed at room temperature. Maximum energy storage density Wrec ̴ 190.89 mJ/cm3 with an efficiency of 48.63% has been obtained for x = 0.015. A large piezoelectric charge coefficient (d33) of 460 pC/N has been obtained for x = 0.020. The room temperature magnetic measurements shows feeble ferromagnetism for Mn doped samples. These studies suggest the application of these ceramics for multilayer ceramic capacitors, energy storage, and high power applications.

High-Temperature Dielectric and Relaxation Behavior of Tantalum-Doped Sodium Bismuth Titanate-Barium Titanate Ceramics

Ta-doped 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 [(1 − x)(0.94BNT–0.06BT) − xTa (x = 0.00–0.02)] ceramics were prepared by a solid-state reaction process. X-ray diffraction (XRD) shows a rhombohedral symmetry with space group R3c for all samples. The introduction of Ta moves the low-temperature dielectric anomaly to lower temperature while the high-temperature dielectric anomaly becomes broader, although the dielectric permittivity is depressed slightly. Dielectric permittivity (ɛr) as a function of temperature for the sample x = 0.02 shows a stable and broad relative permittivity ∼ 3500 from 50 °C to 400 °C with low dielectric loss (tanδ) ≤ 0.02 from 80 °C to 340 °C (at 1 kHz). A Debye-like relaxation was found in the paraelectric region. The activation energy of relaxation frequency (Ea) of the samples x = 0, 0.005, 0.01, 0.02 is 0.62 eV, 0.84 eV, 1.15 eV and 1.20 eV and the activation energy of conduction (Econ) is 0.56 eV, 0.72 eV, 0.89 eV and 0.90 eV for x = 0.00, x = 0.005, x = 0.01 and x = 0.02, respectively, which are derived from isothermal impedance spectroscopy and admittance spectroscopy, respectively. The dielectric relaxation behavior is related to the migration of oxygen vacancies and cation vacancies dependence on the concentration of Ta.

Magnetoelectric and magnetodielectric coupling in partially Ni-doped CoFe2O4 and 0.15(Ba0·7Ca0·3TiO3)–0.85(BaZr0·2Ti0·8O3) composites prepared via clean microwave sintering

Multiferroic composites with high magnetoelectric coupling at room temperature are considered as the most significant materials due to their potential application in many electronic devices. Furthermore, ultrafast, eco-friendly energy-efficient innovative techniques to develop multifunctional materials have attracted abundant importance. In this study, we report on ferrite–ferroelectric particulate composites prepared via clean, eco-friendly, ultrafast, hybrid-microwave sintering. Partially Ni-doped CoFe2O4 was selected as a magnetostrictive phase due to its considerable value of the magnetostriction coefficient, λ11 ≈ −118 ppm, saturation magnetization Ms ≈ 80 emu/gm, and μB ≈ 3.37 and mixed with a 0.15(Ba0·7Ca0·3TiO3)–0.85(BaZr0·2Ti0·8O3) ferroelectric phase in different content ratios of 10%, 20%, 30%, and 40%. The multiferroic properties of the sintered composite samples were investigated considering magnetoelectric and magnetodielectric couplings. The highest value of the magnetoelectric coupling coefficient, αME = 22..09 mV/Oe·cm was observed for the composite with 40% ferrite content, while similar composite exhibits the higher value of the magnetodielectric coupling coefficient which is 3.52% at 1 kHz (frequency) and 1 T (magnetic field). X-ray diffraction and Raman spectroscopy confirmed the phases of the ferrite and ferroelectric constituents without revealing any additional phases. The impedance and AC conductivity of the multiferroic compositions were analyzed under various temperatures and by applying a magnetic field at room temperature. The temperature-dependent dielectric nature confirms that the addition of Ni-doped CoFe2O4 into a ferroelectric constituent substantially influences the dielectric constant in the paraelectric region. These results may offer an alternative technique for the preparation of multiferroic composites with improved coupling properties.

Large Piezoelectric Response in Hybrid Rare-Earth Double Perovskite Relaxor Ferroelectrics.

Piezoelectric materials are technologically important, and the most used are perovskite ferroelectrics. In recent years, more and more emerging areas have put forward new requirements for piezoelectric materials, such as light weight, low acoustic impedance, good flexibility, and biocompatibility. In this context, hybrid organic-inorganic perovskite ferroelectrics have emerged as promising supplements, because they combine attractive features of inorganic and organic materials. Among them, hybrid double-metal perovskites have recently been found to exhibit excellent ferroelectricity. However, their potential as piezoelectric materials has not been exploited. Here, we describe large piezoelectric response in hybrid rare-earth double perovskite relaxor ferroelectrics (RM3HQ)2RbLa(NO3)6 and (RM3HQ)2NH4La(NO3)6 (RM3HQ = R-N-methyl-3-hydroxylquinuclidinium). They are simultaneously ferroelectric and ferroelastic crystals, with the R3 ferroelectric phase and P213 paraelectric phase. We found that ferroelectric polar microdomains and paraelectric nonpolar regions coexist in a wide temperature range through variable-temperature piezoresponse force microscopy images. The two-phase coexistence reveals low energy barriers of transitions between the two phases and between the polar microdomains with different polarization directions. These lead to the easy polarization rotation of the polar microdomains upon applying a stress and, accordingly, the large piezoelectric response up to 106 pC N-1 for (RM3HQ)2RbLa(NO3)6. This finding represents a significant step toward novel applications of piezoelectric materials based on lead-free hybrid perovskites.

Field-induced ferroelectricity in paraelectric phase of Barium strontium titanate

The nonlinear polarization and ferroelectricity in the paraelectric region of Ba0.7Sr0.3TiO3 ceramic samples are investigated. For this, samples are poled at a finite field and field-induced phase is analyzed through XRD, SEM, dielectric, impedance, and Piezo force microscopy high-frequency studies before and after poling. The Rayleigh-like dynamics is inspected along with the switching behavior in to samples. Our study suggests field-induced ferroelectricity in Ba0.7Sr0.3TiO3 due to polar distortion.

Correlation between orthorhombic distortion with relaxation and Conduction mechanism of Gd3+ modified SrBi4Ti4O15 ceramics

Aurivillius single-phase ceramics of Gd3+ substituted SrBi4Ti4O15 with nominal formula of Sr1-xGd2×/3Bi4Ti4O15 (where x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.1) herein denoted as SGBT-x have been prepared by using mixed oxide technique. The primary structural analysis from XRD study confirms that orthorhombic distortion to increase with increase in Gd-content, which was strongly supported by Raman spectroscopy. Two of the relaxation mechanisms were clearly identified from cole-cole plot and modulus spectroscopy analysis, which could be discerned to both grain and grain boundary contributions effect. The kinetic study of frequency dependent AC conductivity at various temperature was investigated by using Jonscher's power law equation, σtot(ω)=A(T) ωs + σDC(T); where 0 < s < 1. Close resemblance of obtained activation energy from relaxation mechanism, DC conductivity as well as hopping conduction below transition temperature (TC) suggested that the transport behavior is to originate from oxygen vacancy related hopping mechanism in SGBT-0.08 specimen. In order to further confirm the possible conduction mechanisms in the system the 's' exponent has also been analyzed detail at different temperature regions. Overall we examine that CBH (correlated barrier hopping) and NSPT (non-overlapping small polaron) are two of the appropriate models for conduction process in ferroelectric and paraelectric region respectively. Also the orthorhombic distortion (b/a) of SGBT system plays a major role in the conduction and relaxation process.

SYNTHESIS AND PROPERTIES OF NIOBIUM-, COBALT-SUBSTITUTED SOLID SOLUTIONS OF BISMUTH TITANATE WITH LAYERED PEROVSKITE STRUCTURE

The Bi4Ti3–2xNbxCoxO12 (x = 0.05, 0.10, 0.15) solid solutions have been synthesized using ceramic method, their crystal structure, thermal expansion, electrical and dielectric properties have been studied. It has been established that Bi4Ti3–2xNbxCoxO12 titanates are p-type semiconductors whose electrical conductivity at low temperatures is higher, but at high temperatures is lower than for the base Bi4Ti3O12 bismuth titanate. It has been found that partial co-substitution of titanium by niobium and cobalt in Bi4Ti3O12 leads to the increase in the size of the unit cell of the Bi4Ti3–2xNbxCoxO12 solid solutions, a decrease in their Curie temperature, a decrease in the dielectric constant and dielectric losses, and slightly affects the magnitude of their linear thermal expansion coefficient. For Bi4Ti3.8Nb0.1Co0.1O12 and Bi4Ti3.7Nb0.15Co0.15O12 solid solutions, a sharp increase in the activation energy of electrical conductivity has been observed at the transition from the ferroelectric region to the paraelectric region.

Electrical properties of sodium and neodymium modified SrBi4Ti4O15 piezoelectric ceramics

ABSTRACTFerroelectric ceramic Sr0.8Na0.1Nd0.1Bi4Ti4O15 (SNNBT) is prepared by solid state reaction method. Single phase formation with orthorhombic structure is confirmed by X- Ray diffraction analysis. Scanning electron micrograph of the ceramic shows the plate like grains of different sizes. Dielectric properties and phase transitions are studied. Relationship of Curie temperature with ionic radii of elements is discussed. Cole-Cole plots of impedance suggest the relaxation to be non-Debye type. The activation energies are obtained in Ferro and Para electric regions from the temperature variation of dc conductivity. Piezoelectric parameters have been measured on well-densified and poled samples. This study shows that SNNBT is a proficient ceramic for applications at high temperatures.

Curie point and a space charge relaxation in ferroelectric poly(vinylidene fluoride‐trifluoroethylene) copolymers with different thermal history

ABSTRACTHigh‐temperature processes of space charge relaxation in films of poly(vinylidene fluoride‐trifluoroethylene) (70–30) have been investigated. The films were prepared by the crystallization from a solution in tetrahydrofuran at a room temperature. X‐ray data analysis showed that initial films crystallize in metastable state: a paraelectric phase is formed at fast crystallization below the Curie temperature. An exothermic process was observed at heating, indicating a solid‐state crystallization of metastable paraelectric regions. This process is controlled by melting of ordered regions formed at secondary crystallization. These transformations of structure affect characteristics of the high‐temperature space charge relaxation process. In particular, it was found that activation energy of extrinsic conductivity is reduced by several times in the region of ferroelectric‐paraelectric phase transition. An additional relaxation process was registered above the Curie temperature, which is caused by the relaxation of charges in double electric layer formed on an interface between an electrode (Au) and fluorine‐containing polymer. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46186.

Modification of structural and electrical properties of Ca element on barium titanate nano-material synthesized by hydrothermal method

ABSTRACTBa1-xCaxTiO3 (x = 0.10, 0.15, 0.20 and 0.25) ceramics were prepared by using standard Sol-Gel hydrothermal reaction technique at 150°C. Structural and dielectric properties were carry out by using X-ray diffraction and dielectric constant, tangent loss and conductivity measurements. Single-phase perovskite-type X-ray diffraction patterns were observed and the samples have a phase with a tetrahedral structure at room temperature for all the compositions. SEM image of Ba1-xCa xTiO3 powder shows inhomogeneity with the increment of Ca element. Small grains with average grain sizes of ∼20 ± 5 nm uniformly distributed over the mesocrystals. The temperature dependence of the dielectric permittivity of tetrahedral Ba1-xCaxTiO3 ceramic as a function of frequency (1 kHz-100 kHz) at different temperature (RT–300°C) provided useful information on electrical behavior (Ferroelectric-Relaxor relationship). The behavior of the dielectric graph (in paraelectric region) confirmed the relaxor behavior of the material at high temperature (160–300°C) range. Nature of diffusivity graph also indicating that, increase of Ca content improved the diffusivity of materials. Values of Tm increased with increasing x = 0.10– 0.25, from ∼120°C to 140°C. In the comparison of other, the composition Ba0.90Ca0.10TiO3 reveals strong results. It has dielectric permittivity (ϵ) 5741 ± 200 at the low value of loss tanδ = 0.009 ± .091 along with the transition temperature (Tc) at ∼131 ± 2 shows diffusivity 1.72 ± 10 < 2 and activation energy 0.821 ± .030.

Quantum Paraelectric States in SrTiO3and KTaO3: Barrett Model, Vendik Model, and Quantum Criticality

The dielectric constants of the quantum paraelectrics SrTiO3 and KTaO3 are measured between 4 and 325 K. Their temperature dependences are analyzed on the basis of the Barrett and Vendik models. The former model deals with a ferroelectric optical mode coupled with other optical modes, whereas the latter deals with the mode coupled with acoustic modes. In addition, the latter contains a measure of the density of defects and inhomogeneity. The dielectric constants at low temperatures can be accurately described using Vendik’s formula; however, they cannot be accurately described using Barrett’s formula, even after the introduction of a measure of the density of defects and inhomogeneity. A critical quantum paraelectric region has been introduced recently between a classical region and a quantum paraelectric one. We point out that the critical region is where a low-temperature approximation is well realized for the model with the coupling between the ferroelectric and acoustic modes.

Possible coexistence of cycloidal phases, magnetic field reversal of polarization, and memory effect in multiferroic R0.5Dy0.5MnO3 (R = Eu and Gd)

We report the occurrence of both ab and bc cycloidal ordering of Mn-spins at different temperatures and their possible coexistence at low temperatures in the polycrystalline mixed rare-earth compounds, R0.5Dy0.5MnO3 (R = Eu and Gd), which exhibit extraordinary magnetoelectric properties. While the polarization of Gd0.5Dy0.5MnO3 is comparable to TbMnO3, the compound Eu0.5Dy0.5MnO3 shows high value of polarization. However, both of them show giant magnetic tunability and exhibit large magnetocapacitance whose sign changes across the two cycloidal ordering temperatures. Intriguingly, the electric polarization can be reversed upon ramping up or ramping down the magnetic field, which has not been observed for any of the RMnO3 system. Most strikingly, these compounds show non-volatile ferroelectric memory effect even in the paraelectric and paramagnetic region (TC ≤ T ≤ 80 K). We attribute these remarkable properties to the coexistence of ab and bc cycloidal ordered phases.

Effect of Eu Doping on the Structural, Electrical, and Dielectric Properties of K0.5Na0.5NbO3 Ceramics for High-Temperature Capacitor Applications

The structural and dielectric properties of Eu-doped K0.5Na0.5NbO3 (KNN) ceramics were investigated as a potential candidate for use in high-temperature capacitors with working temperature beyond 200°C. x-Ray diffraction results showed that tetragonal and cubic structure distortions occurred for low- and high-concentration doping, respectively. With increase of Eu content, the dielectric anomaly of the tetragonal–cubic transition was depressed and shifted to low temperature, while the temperature of the orthorhombic–tetragonal transition remained unchanged. A dielectric relaxation associated with oxygen vacancies was detected in the paraelectric phase region. The activation energy of oxygen vacancies depended on the Eu concentration and the defect compensation mechanism. KNN doped with 3 mol% Eu (KNN3Eu) showed good dielectric temperature stability (±10%) with relatively high permittivity (>1800 at 225°C) over the temperature range from 119°C to 495°C, representing a good starting point for development of high-temperature capacitor materials.

Suppressed ferroelectric relaxor behavior of Mn‐modified Ba(Zr0.3Ti0.7)O3 relaxor ceramics

MnCO3‐modified Ba(Zr0.3Ti0.7)O3 relaxor ferroelectric ceramics were fabricated by using the solid‐state reaction method. The temperature dependences of electrical and dielectric properties of the ceramics were systematically investigated over the range −140 to 400 °C. The typical ferroelectric relaxor behavior of the Ba(Zr0.3Ti0.7)O3 ceramics was greatly suppressed by adding a proper amount of MnCO3. The suppressed relaxor behavior can be restored by annealing the samples in air, which is attributed to the presence of oxygen vacancies in the samples. In the paraelectric phase region, the low‐frequency dielectric relaxations associated with oxygen vacancies are observed above room temperature, and increase with increasing of Mn content. Compared to the undoped Ba(Zr0.3Ti0.7)O3 ceramic, Mn‐doped samples display excellent temperature stability in a wide temperature. The critical composition of x = 0.05 (MnCO3) not only exhibits a lower degree of ferroelectric relaxor behavior (ΔTm = 5.6 K), but also maintains a relatively higher tunability (66.9%@30 kV cm−1) than that of pure Ba(Zr0.3Ti0.7)O3 (ΔTm = 16.5 K, 49.6%@30 kV cm−1).