First-order Ferroelectric Phase Transition Research Articles

Distortion modes and ferroelectric properties in hybrid improper ferroelectric Sr3(Sn,Zr)2O7 ceramics

In the present work, the distortion modes and ferroelectric properties of Sr3(Sn1−xZrx)2O7 (x = 0.0, 0.25, 0.5, 0.75, 1.0) ceramics with double-layered Ruddlesden–Popper structures were investigated. The amplitudes of three distortion modes for the ferroelectric phase deviated from the aristotype one were quantified using the symmetry-mode approach adopted in Rietveld refinement against x-ray diffraction patterns. The remanent polarization and the coercive field decreased with increasing the content of Zr4+ cations. The decline of polarization should attribute to the nonpolar secondary phase, while the suppression of a coercive field may connect with the decreased amplitude of the rotation mode. The Curie temperatures increased linearly with increasing x value in Sr3(Sn1−xZrx)2O7 ceramics, inducing from the decline of a tolerance factor. A typical first-order improper ferroelectric phase transition was determined using a differential scanning calorimetry measurement and dielectric characterization. From the present work, a straightforward way to quantify the amplitude of a distortion mode for the ferroelectric phase was given, and the ferroelectric properties could be effectively tuned by substituting the cations at the B site in the Sr-based hybrid improper ferroelectrics.

Coexisting Mechanisms for the Ferroelectric Phase Transition in Li2SrNb2O7

Pseudo-Ruddlesden–Popper-type Li2SrNb2O7 (LSNO), which belongs to a layered perovskite-type family, exhibits a first-order ferroelectric phase transition at 217 K. Our first-principles calculations...

Improved ferroelectric properties in hybrid improper ferroelectric Sr3−xBaxZr2O7

In the present work, Sr3−xBaxZr2O7 (x = 0.1, 0.2, 0.3) ceramics with Ruddlesden-Popper structures were prepared by a standard solid-state reaction method. The refinement results showed that the present ceramics formed a single orthorhombic phase with A21am space groups. The lattice constant and tolerance factor increased while the Curie temperature decreased linearly with increasing the content of barium cations, and the typical first-order improper ferroelectric phase transitions were determined in all ceramics. Moreover, the declines of oxygen octahedral rotation angle and coercive field were observed, while the enhanced remanent polarizations were found, therefore the improved ferroelectric properties were achieved by introducing the barium cations. The sharper decline of Curie temperature was induced by the hetero-valent substitution in contrast to the universal relationship between Curie temperature and tolerance factor. From the present work, the tolerance factor could not determine ferroelectric properties, and the possible way to improve ferroelectric properties was explored for Sr3Zr2O7-based ceramics.

Elastic and anelastic properties of vinylidene fluoride-trifluoroethylene (VDF-Tr) copolymers in the vicinity of phase transition

Temperature dependences of internal friction Q−1 and elastic modulus E of the VDF60Tr40 copolymer were studied in the temperature range of 20–100 °C at a frequencies f ≈ 3–17 Hz. A distinct softening of the modulus E was found near the Curie temperature. In the vicinity of 60 °C, a wide maximum of Q−1 is revealed, which is a superposition of two Q−1 peaks. The “low-temperature” peak of internal friction is due to the process of α-relaxation in the non-crystalline polymer fraction. “High-temperature” one is associated with a first-order ferroelectric phase transition in the crystalline fraction.

Lead-free molecular ferroelectric [N,N-dimethylimidazole]3Bi2I9 with narrow bandgap

Lead-based organic-inorganic hybrid perovskite materials are widely applied in solar cells due to their excellent optoelectronic properties. These materials usually appear ferroelectricity with the built-in electric field, which can be used to improve the power conversion efficiency (PCE) of solar cells. However, the toxicity of lead has severely hampered their applications. Hence, it is of utmost significance to explore novel organic-inorganic hybrid perovskite materials with non-toxicity, ferroelectricity, and narrow bandgap at room temperature to enhance the PCE for broad practical applications. Herein, we reported a lead-free hybrid molecular ferroelectric material, i.e. (C5N2H9)3Bi2I9, with zero-dimensional perovskite-like structure. (C5N2H9)3Bi2I9 undergoes first-order ferroelectric phase transition with a Curie temperature of 327 K. Moreover, the dielectric constants of (C5N2H9)3Bi2I9 exhibit a step-like anomaly varied between the high-temperature paraelectric phase and the low-temperature ferroelectric phase. Furthermore, (C5N2H9)3Bi2I9 demonstrates a narrow bandgap of 2.1 eV. Hence, the as-reported novel member of the organic-inorganic hybrid family renders great promise for optoelectronic devices.

Rational analysis of processes of (first-order) ferroelectric phase transition and those of ferroic hysteresis

From the view-point of non-equilibrium (or irreversible) statistical thermodynamics, the similarities and differences between the processes of (first-order) ferroelectric phase transition and those of ferroic hysteresis were compared. They are all irreversible. The former are local and rate-dependent, at the meanwhile, the latter are non-local and rate-independent.

Electrocalorics hit the top.

A first-order ferroelectric phase transition is driven supercritically in multilayer capacitors of PbSc0.5Ta0.5O3, enabling an electrocaloric response of 5.5 K near room temperature.

Large electrocaloric effects in oxide multilayer capacitors over a wide temperature range.

Heat pumps based on magnetocaloric and electrocaloric working bodies-in which entropic phase transitions are driven by changes of magnetic and electric field, respectively-use displaceable fluids to establish relatively large temperature spans between loads to be cooled and heat sinks1,2. However, the performance of prototypes is limited because practical magnetocaloric working bodies driven by permanent magnets3-5 and electrocaloric working bodies driven by voltage6-16 display temperature changes of less than 3kelvin. Here we show that high-quality multilayer capacitors of PbSc0.5Ta0.5O3 display large electrocaloric effects over a wide range of starting temperatures when the first-order ferroelectric phase transition is driven supercritically (as verified by Landau theory) above the Curie temperature of 290kelvin by electric fields of 29.0volts per micrometre. Changes of temperature in the large central area of the capacitor peak at 5.5kelvin near room temperature and exceed 3kelvin for starting temperatures that span 176kelvin (complete thermalization would reduce these values from 5.5 to 3.3kelvin and from 176 to 73kelvin). If magnetocaloric working bodies were to be replacedwith multilayer capacitors of PbSc0.5Ta0.5O3,then the established design principles behind magnetocaloric heat pumps could be repurposed for better performance without bulky and expensive permanent magnets.

Electrocaloric Cooling Cycles in Lead Scandium Tantalate with True Regeneration via Field Variation

There is growing interest in heat pumps based on materials that show thermal changes when phase transitions are driven by changes of electric, magnetic or stress field. Importantly, regeneration permits sinks and loads to be thermally separated by many times the changes of temperature that can arise in the materials themselves. However, performance and parameterization are compromised by net heat transfer between caloric working bodies and heat transfer fluids. Here we show that this net transfer can be avoided-resulting in true, balanced regeneration-if one varies the applied electric field while an electrocaloric (EC) working body dumps heat on traversing a passive fluid regenerator. Our EC working body is represented by bulk PbSc0.5Ta0.5O3 (PST) near its first-order ferroelectric phase transition, where we record directly measured adiabatic temperature changes of up to 2.2 K. Indirectly measured adiabatic temperature changes of similar magnitude were identified, unlike normal, from adiabatic measurements of polarization, at nearby starting temperatures, without assuming a constant heat capacity. The resulting high-resolution field-temperature-entropy maps of our material, and a small clamped companion sample, were used to construct cooling cycles that assume the use of an ideal passive regenerator in order to span $\leq$20 K. These cooling cycles possess well defined coefficients of performance that are bounded by well defined Carnot limits, resulting in large ($>$50%) well defined efficiencies that are not unduly compromised by a small field hysteresis. Our approach permits the limiting performance of any caloric material in a passive regenerator to be established, optimized and compared; provides a recipe for true regeneration in prototype cooling devices; and could be extended to balance active regeneration.

Red shift of absorption edge and band gap shrinkage in perovskite Pb(Zr0.35Ti0.65)O3 thin film from heat generation for solar cells application

We have experimentally investigated the temperature dependent optical properties of Pb(Zr0.35Ti0.65)O3 (PZT) perovskite thin film for simulating heat generation in light harvesting. During the evolution of optical properties with temperature from 293 K to 643 K, the red shift of absorption edge and band gap shrinkage phenomena have been found by ellipsometry measurement, which is due to the renormalization of crystal structure under thermal disturbance. In addition, the abrupt change of band gap has happened at 550 K, which is in accord with the first-order ferroelectric phase transition in PZT thin film.

Magnetoelectric effect in Sm-substituted tungsten bronze structure Ba4(SmxLa1-x)2Fe2Nb8O30 ceramics

Magnetoelectric effect is directly measured in the Ba4(SmxLa1-x)2Fe2Nb8O30 ceramics, which is rarely reported in tungsten bronze ceramics. Besides, the effects of Sm-substitution on the crystal structure, dielectric, ferroelectric and magnetic properties have been systematically studied. XRD Rietveld refinement confirms all the ceramics to be single phase with space group of P4bm. With the increase of x, Ba4(SmxLa1-x)2Fe2Nb8O30 ceramics transform from paraelectric to ferroelectric. The compositions of x = 0.9, 0.95 and 1 show first-order ferroelectric phase transitions above room temperature. Compared to composition x = 0, the dielectric constant of other compositions exhibits frequency stability and the dielectric loss decreases apparently at room temperature. The ferroelectricity improves with increasing x, which can be ascribed to the increased A2-A1 ionic radius difference. Meanwhile, the magnetic hysteresis loops are obtained for some compositions. All the results approve Ba4(SmxLa1-x)2Fe2Nb8O30 (x = 0.9, 0.95, 1) ceramics as room temperature multiferroic materials with intrinsic magnetoelectric effect.

Linear and nonlinear dielectric response of the first-order ferroelectric phase transition in K0.92Li0.08TaO3 under dc electric field

The results of measurements of low-temperature susceptibility: linear and nonlinear, and polarization under dc electric field of the lithium-doped potassium tantalate K0.92Li0.08TaO3 (KLT-8%Li) solid solution are presented. The recognized coexistence of the relaxor-like and ferroelectric behavior is presented. The observed ferroelectric phase transition is of the first-order type. Using an external dc electric field Edc = 178 kV/m the temperature of the ferroelectric phase transition is shifted by 3 K toward the value of 117 K, relative to the TC = 114 K observed without external dc electric field. Experimental facts reported in the present paper allowed us to argue that ferroelectricity in K1-xLixTaO3, in the case of x > 0.022 is due to a dynamical correlation of the off-center motions of Ta+5 ions in the octahedral environment of oxygen ions and does not arise directly as a result of the ordering of Li+ ion dipole moments within the so-called polar nanoregions.

Specific Features of the Structure and Properties of High-Temperature Oxide Materials Based on Bismuth Sodium Titanate

Single-phase ceramic samples from the region of morphotropic phase boundary in the (1–x)(Na0.5Bi0.5)TiO3–xBaTiO3 and (1–y)[(Na0.5Bi0.5)TiO3–xBaTiO3]–yBi(Mg0.5Ti0.5)O3 systems, modified by low-melting LiF and 0.6NaCl–0.4LiF additives, have been prepared by solid-state synthesis. The effect of additives on the phase formation, structural parameters, and dielectric and ferroelectric properties of the ceramics has been studied. A decrease in the ceramic sintering temperature is found. A slight increase in the unit-cell volume upon modification of the ceramics under study by lithium fluoride and 0.6NaCl–0.4LiF additive is revealed. First-order ferroelectric phase transitions near 700–800 K have been observed. The prospects for improving the piezoelectric properties of modified ceramic samples are proved.

Large pyroelectric and thermal expansion coefficients in the [(CH3)2NH2]Mn (HCOO)3 metal-organic framework

The [(CH3)2NH2]Mn(HCOO)3 perovskite metal-organic framework exhibits a first-order ferroelectric phase transition with a high polarization at Tc ∼ 192 K, induced by the order-disorder transition of hydrogen bonds. Accompanying this sharp phase transition, a huge pyroelectric coefficient with a peak value of 5.16 × 10−2 C/m2 K is detected. In addition, there is a large lattice expansion along the [012] direction at Tc, resulting in a giant linear thermal expansion coefficient as high as 35 000 ppm/K. These striking results indicate that ferroelectric metal-organic frameworks combing both merits of inorganic and organic compounds hold a great potential in generating superior pyroelectric and thermal expansion properties.

Thermal effects in the vicinity of phase transition temperatures in matrix-isolated sodium nitrite NaNO2

Thermal effects in some nanoporous silicate matrices (with different pore sizes) loaded with ferroelectric NaNO2 from both a saturated solution and from a melt have been studied in a wide temperature range including the phase transition temperatures. All the samples reliably demonstrate maxima of the heat capacity, corresponding to first-order ferroelectric phase transitions. The characteristics of the maxima (intensity, half-width, phase transition temperature, etc.) have been determined. A more complex situation is the observation of an incommensurable phase (sinusoidal antiferroelectric), in particular, in the case of pore sizes comparable to the period of an “incommensurable” wave, the manifestation of which can be explained by the appearance of a corresponding orientation of sodium nitrite nanocrystals in pores of these matrices. It is found that the characteristics of above noted effects depend on the prehistory of the samples under study.

Single crystal growth of β-Tb2(MoO4)3 and its evaluation

ABSTRACTA single crystal of β-terbium molybdate, β-Tb2(MoO4)3 (TMO), was grown using the floating zone (FZ) method. The single crystal is transparent and light green. To evaluate the single crystal, it was subjected to powder X-ray diffraction measurements. Rietveld refinement was performed for the diffraction pattern. In addition, studies of its heat capacity were performed. The first-order ferroelectric and ferroelastic phase transition temperature, TC, was found to be 431.98 K. The results show that the grown crystal is the single-phase, high quality TMO.

Ferroelectric phase transition and electrical conduction mechanisms in high Curie-temperature PMN-PHT piezoelectric ceramics

Ferroelectric phase transition characteristic and electrical conduction mechanism of the high Curie-point (TC) 0.15Pb(Mg1/3Nb2/3)O3−0.4PbHfO3−0.45PbTiO3 (PMN-PHT) piezoelectric ceramics were studied by the temperature dependent Raman spectra and electrical properties. Sole first-order ferroelectric phase transition is demonstrated by the thermal hysteresis behavior of the temperature dependent dielectric constant and the dramatic drop of the derivative of inverse dielectric constant ξ= d(1/εr)/dT around TC in the PMN-PHT ceramics. The temperature dependent Raman spectroscopy not only provides further evidence for the ferroelectric to paraelectric phase transition appearing around TC in the PMN-PHT ceramics, but also reveals the successive phase symmetry changes of the polar nanoregions (PNRs), in which apparent anomalies appear in the Raman peaks' wavenumber, wavenumber distance, intensity, intensity ratio, and line width of some selected Raman modes upon heating. Typical sole cole-cole circle is obtained for the PMN-PHT ceramics in the temperature range of 440–560°C, based on which the activation energy (Ea) of the electrical conduction is calculated being ~1.2eV. Such low value of Ea indicates that the oxygen vacancies formed in the PHT-PMN ceramics induced by the evaporation of Pb during the sintering process dominate the high-temperature extrinsic electrical conduction.

Origin of the first-order ferroelectric phase transition in K0.957Li0.043TaO3 solid solution

The results of low-temperature linear and nonlinear susceptibilities and polarization measurements of the KLT-4.3%Li crystalline sample are presented. The following model of the mechanism of the ferroelectricity in the K0.957Li0.043TaO3 (KLT-4.3%Li) solid solution is proposed. Static quasi-frozen clusters of Li+ dipoles affect the ordering process of the remainder of the system: a dynamical correlation of the off-center motions of Ta ions along one of the equivalent off-center sites in the 〈111〉 cubic direction in the octahedral environment of O ions occurs and leads to the formation of a reversible spontaneous polarization.

Effect of a weak external electric field on the kinetics of the ordering of ferroelectrics upon first-order phase transitions

The kinetics of the formation and growth of 180° domains in a weak quasi-stationary external electric field has been considered in the framework of the phenomenological Ginzburg–Landau model using the example of sodium nitrite (NaNO2) crystals that undergo a first-order ferroelectric phase transition of the order–disorder type. The influence of the rate and temperature of quenching, as well as the strength of an external electric field, on the subsequent evolution of the system toward the thermodynamic equilibrium state has been analyzed. It has been shown that, by varying a weak external electric field applied to the ferroelectric crystal after quenching, it is possible to obtain both single-domain and multi-domain ordered structures. It has been established that the formation of nonequilibrium (“virtual”) multi-domain structures of the asymmetric type is possible for particular strengths of the electric field applied to the ferroelectric after quenching. A similar effect can be achieved by varying the depth of quenching of the sample. It has been found that, if the size of the order parameter inhomogeneities formed at the stage of quenching does not exceed a critical value, they can be reoriented partially or completely into domains of opposite sign. For this purpose, the relaxation after quenching should be performed in an external electric field of the appropriate sign.

Phase-transition character in (Ba0.50,Sr0.50)TiO3 nanodots from first principles

A first-principles-derived scheme combined with an efficient Monte Carlo technique is performed to investigate the character of phase transitions in (Ba0.50,Sr0.50)TiO3 (BST50) nanodots under ideal short-circuit (SC) and open-circuit (OC) electrical boundary conditions, and the corresponding properties are subsequently compared to the properties of bulk BST50. Our calculations indicate that the ferroelectric properties change dramatically when transitioning from 3D (bulk) to 0D (nanodot) systems under short-circuit conditions. While BST bulk exhibits three first-order ferroelectric phase transitions, BST dot shows a single second-order ferroelectric phase transition. On the other hand, new insight into the character and signature of the phase transition associated with a toroid moment of polarization, which occurs in nanodots under open-circuit conditions, is provided.