Ferro-paraelectric Phase Transition Research Articles

Effect of substitution on the structural, electrical properties, and dielectric relaxor behavior in lead-free BiFeO3-based ceramics.

BiFeO3-based ceramics have recently garnered much interest among researchers owing to their valuable and outstanding characteristics. For this reason, the 0.7(Na0.5Bi0.5)TiO3-0.3(Bi0.7Sm0.3FeO3) ceramic was successfully synthesized by a solid-state route. The central purpose of this research is to investigate the substitution influence of Na, Ti, and Sm on the structural, dielectric, and electric properties of 0.7(Na0.5Bi0.5)TiO3-0.3(Bi0.7Sm0.3FeO3), as well as to explore its potential applications as it exhibits multiple novel functions. Notably, a structural transition from rhombohedral R3c to orthorhombic P4mm occurred within this material. In this respect, a suitable equivalent electrical circuit was invested to assess the contributions of grains and grain boundaries to the complex impedance results. Electrical conductivity was attributed to the correlated barrier hopping (CBH) motion of the oxygen vacancies in the sample. The temperature dependence of the dielectric constants revealed the presence of a phase transition. The local disorder provides a dependence of the real part of the permittivity on the frequency which characterizes a relaxor ferroelectric-type behavior of a lead-free material. The modified Curie-Weiss law, in addition to the Vogel Fulcher and Debye law relationships, was utilized to analyze the diffuse transition phase. Furthermore, the studied compound displayed promising electrical properties and chemical stability and proved to be a good relaxor. In this regard, a correlation between dielectric and electric behavior near the ferro-paraelectric phase transition was established.

Electrical and Ferroelectric Properties of Undoped and Er-Doped PZT52/48 Electroceramics Synthesized by a Polymeric Precursor Method

The effect of Er on the structural and electrical properties of doped PZT 52/48 ceramics has been studied in this work. The ferroelectric properties (permittivity, ferro-paraelectric phase transition and hysteresis) of such materials are thus found to be strongly dependent on the degree of densification and structural phase development during sintering at high temperatures. In particular, the nature of the ferroelectric to paraelectric phase transition is in these materials that can be represented through the Curie-Weiss Law equation modified, appropriate for the characterization diffuse transitions. The substitution of Er3+ for (Zr,Ti)4+ is found to induce strong diffuse phase transition in these materials. The electrical properties reported in this work are in magnitude comparable to those exhibited by PZT52/48 materials.

Synthesis, crystal structure and phase transition in a perovskite type (CH3NH3)2M(X)2(Y)2(M=Sn; X=SCN; Y=Cl)

The exploration of ferroelectric hybrid materials is highly appealing due to their great technological significance. In line with this, we herein report the development of a new ferroelectric relaxor: (CH3NH3)2Sn(SCN)2Cl2 was synthesized and studied by single-crystal X-ray diffraction, powder XRD, Differential scanning calorimetry (DSC), IR spectroscopy and dielectric measurements. The phase purity was confirmed by Rietveld refinement of the X-ray powder diffraction pattern. It crystallizes, at room temperature, in the orthorhombic system with the Pnm21 space group. The crystal structure is formed of discrete ionic entities (CH3NH3)+ and (Sn(SCN)2Cl2)2-. The methylammonium cations are bonded to these chains by hydrogen-bonding contacts. DSC measurement shows that this compound exhibits a diffuse ferro–paraelectric phase transition around 355 K. Dielectric study exhibits a relaxor behavior characterized by the transition temperature shifts toward higher temperature with the rise of frequency. This behavior was validated by the modified Curie–Weiss law. The diffuseness parameter was the γ is approach to 1.96 at 2000 KHz.

Enhancement of piezocatalytic activity at the ferro-paraelectric phase transition of Ba1-xSrxTiO3 nanopowders

Nanocrystalline Ba1-xSrxTiO3 (x = 0–0.3) powders were investigated with special interest in their piezocatalytic performance for degradation of organic pollutants. A great improvement of piezocatalytic activity was obtained for the compositions x = 0.2, in which the polarization shows a large change under external stress. Furthermore, with the increase of working environment temperature, the piezocatalytic performance of Ba0.8Sr0.2TiO3 increases firstly and then decreases, giving the best piezocatalytic performance near its Curie temperature. For a better understanding of the piezocatalytic mechanism, the dynamics of charge carriers transfer on solid/liquid interface was discussed with respect to activation energy and overpotential of catalyst. It was suggested that the enhanced piezocatalytic activity of Ba1-xSrxTiO3 comes from two aspects: (1) the overpotential provided by the piezoelectric effect decreases with the increasing Sr content, (2) the activation energy for the piezocatalytic reaction is greatly reduced at ferro-paraelectric phase transition. Combination of these two aspects gives rise to the nonlinear dependence of piezocatalytic activity on Sr content.

Density dependent ionic transport in polycrystalline SrNb2O6 ceramic

The micro-structural as well as electrical behavior of polycrystalline SrNb2O6(SN) are explored in article with changing sintering time. The Rietveld refinement of room temperature x-ray diffraction data reveals monoclinic phase of calcined powder at 1130 °C and the diffraction peaks shift toward lower angle with raising temperature. Furthermore, the article shows single anomaly at 25 °C that attributes to a ferro-paraelectric phase transition, which is dissent with some researchers but in agreement with high-temperature x-ray diffraction pattern. The microstructural study shows enlargement of average grain size sintering time up to 35 h and then decreases for SN50. The investigation of electrical property reveals the increase in magnitude of Z′ and decreasing trend in ionic conductivity of material with increasing sintering time. The ac conductivity plot is fitted with Jonscher's power law that gives the idea of ionic hopping mechanism. The theoretical approach is employed to understand ionic transport within the material.

Synthesis and investigation of structural, optical, dielectric and electronic properties of a new hybrid: [C13H21N2O2](Cd(SCN)3)

A new ferroelectric relaxor: [C13H21N2O2](Cd(SCN)3) procainium tris(thiocyanato) cadmiate(II) was synthesized and studied by single-crystal XRD. This compound crystallizes in the orthorhombic system with acentric space group Pna21. The crystal structure is formed of discrete ionic entities (C13H21N2O2)+ and [Cd(SCN)3]−. The cadmium atom has 3N3S hexa coordinated octahedral geometry. The sulfur atoms and the nitrogen atoms are in facial mode (fac). Each pair of cadmium atoms is triply bridged by μ-1,3-SCN–bridge. Consequently, a linear polymeric chain is formed. The procainium cations are bonded to these chains by hydrogen-bonding contacts and π–ring interaction. DSC measurement shows that this compound exhibits a diffuse ferro–paraelectric phase transition around 356 K. Dielectric study exhibits a relaxor behavior characterized by the transition temperature shifts toward higher temperature with the rise of frequency. This behavior was validated by the Vogel–Fulcher relationship and the modified Curie–Weiss law. The diffuseness parameter was γ = 1.96. The optical band gap Eg = 2.20 eV was estimated by diffuse reflection spectroscopy (DRS) investigation.

High critical transition temperature of lead-based perovskite ferroelectric crystals: A machine learning study

Ferroelectrics undergoes a reversible structural phase from the ferroelectric phase to the paraelectric phase when its temperature exceeds the critical temperature namely Curie temperature <i>T</i><sub>c</sub>. As ferro-paraelectric phase transition is always accompanied by heat-flow, dielectric and pyroelectric anomaly, the value of <i>T</i><sub>c</sub> is extremely important for ferroelectrics. In this paper, the Curie temperature of lead-based perovskite ferroelectric solid solution is studied by machine learning methods including kernel ridge regression (KRR), support vector regression (SVR) and extremely randomized trees regression (ETR). We collect the <i>T</i><sub>c</sub> values of 205 different lead-based perovskites from published experimental papers, both simple perovskites with only one type of <i>B</i> site ion and complex perovskites with up to 5 kinds of ions in <i>B</i> position such as PMN-PFN-PZT are gathered. The diversity of our dataset is guaranteed for the good generalization of our model in perovskite solid solution of different complexity. The features are constructed from the physical and chemical properties of the <i>B</i> site elements in corresponding materials. The weighted-average and variance of the elemental properties are calculated and fed to machine learning models. We use the 5 runs of ten fold cross-validation method to evaluate the machine learning models. The hyperparameters are also chosen carefully with the cross-validation to avoid over fitting. The radial basis function kernel is used in both KRR and SVR. The insensitive error in the SVR is set to be 4 which is comparable to the random error in experiment. From our cross-validation, we find that the mean average errors (MAEs) between the predicted and experimental values of the machine learning methods are 14.4 K, 14.7 K, and 16.1 K, respectively. And the root-mean-square errors (RMSEs) are 22.5 K, 23.4 K, 23.8 K, respectively. After the optimization and the evaluation, our three machine learning models are stacked together by averaging the output of each regression model and thus building an ensemble model. The MAE of the ensemble model is 13.9 K. The RMSE of the ensemble model is 21.4 K. The predicted values keep a correlation coefficient of 0.97 with the experimental values. From the variance reduction in ETR, we derive the importance of our features when determining the Curie temperatures. The five most important factors in our ETR model are " weighted-average thermal conductivity”, " weighted-average conductivity”, " variance of specific heat capacity”, " weighted-average element number”, and " weighted-average relative atomic displacement”. We predict the Curie temperatures higher than those of 200000 types of lead-based perovskites after being trained. Now, we provide two ferroelectric materials that may have high Curie temperatures: 0.02PbMn<sub>1/2</sub>Nb<sub>1/2</sub>O<sub>3</sub>-0.98PbTiO<sub>3</sub> (0.02PMN-0.98PT) and 0.02PbGa<sub>1/2</sub>Nb<sub>1/2</sub>-0.02PbMn<sub>1/2</sub>Nb<sub>1/2</sub>O<sub>3</sub>-0.96PbTiO<sub>3</sub> (0.02PGN-0.02PMN-0.96PT). The predicted Curie temperatures of them are 481 ℃ and 466 ℃, respectively.

The photothermoelectric effect of liquid thermoelectrics as a tool for the detection of ferro–paraelectric phase transitions in solids

A new application of the liquid thermoelectrics (LTE) is proposed: the detection of phase transitions in ferroelectric solids. Concretely, the Seebeck effect generated in a known LTE material (dodecanol + 10−1 mol L−1 tetrabutylammonium nitrate) was used as a tool for the detection of the antiferro–paraelectric phase transition of triglycine sulphate (TGS). TGS was selected as a sample because it is a ferroelectric solid with a convenient Curie point close to room temperature (about 49 °C). The advantages of the present method (compared with previously reported investigations performed with solid thermoelectric materials as sensors) are two: (1) no coupling fluid between the sensor and sample is necessary (the liquid sensor–solid sample thermal contact is perfect); (2) the liquid sensor allows for investigations of samples with irregular geometry. Based on the recently developed theory of the photothermoelectric method, the behaviour of the static volume specific heat and dynamic thermal diffusivity, conductivity and effusivity of TGS around the Curie point has been obtained.

Evolution of polar nano-regions under electric field around ferro-paraelectric transition temperature and its contribution to piezoelectric property in Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 crystal

As one of the most pronounced structural features, polar nano-regions (PNRs) is believed to have significant contribution to the outstanding piezoelectric property of relaxor-based ferroelectrics. However, direct experimental investigation on the connection between the PNRs behavior under electric field and piezoelectric responses is still insufficient. In this work, by the combined use of piezoresponse force microscopy, polarization light microscopy, and the electrical property measurements, we investigate the structure evolution from macro-domains to PNRs around ferro-paraelectric phase transition temperature (Tm, 140 °C) in Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal. Most importantly, based on the corresponding analysis of unipolar strain-electric-field (S-E) curves at different temperatures and the direct observation of electric-field-induced structure evolution at Tm, we intensively investigate the response of PNRs to electric field and its contribution to piezoelectric property. We conclude that, under electric field, the active PNRs around Tm first serve as polar seeds to induce macro-domains from the non-polar matrix, then promote the switching of macro-domains. The large-field strain coefficient d33* in these two processes can achieve maximum of about 5410 pm/V and 61710 pm/V at Tm, and gradually decreases at higher temperature with lower PNRs content.

Electrophysical properties of the multicomponent PBZT-type ceramics doped by Sn4+

In the work, the multicomponent Pb0.75Ba0.25(Zr0.65Ti0.35)1-aSnaO3 (PBZT/Sn) ceramics were obtained with various tin amounts (a from the range of 0.0 to 0.1). The densification of the PBZT/Sn ceramic samples was performed using pressureless sintering method. The effect of SnO2 content on the crystal structure of PBZT/Sn ceramics, microstructure, DC electrical conductivity and electrophysical properties (including dielectric and ferroelectric testes), were investigated. The PBZT/Sn ceramic samples exhibit high values of dielectric permittivity at the temperature of ferro-paraelectric phase transition and show the relaxor character of phase transition. Excessive SnO2 contents doping of the PBZT/Sn materials (already for a = 0.1) might lead to lattice stress and structure defects, which successively leads to the deterioration of ferroelectric and dielectric properties of the ceramic samples. The presented research shows that the addition of SnO2 to the base PBZT compound (in the proper proportion) gives an additional possibility of influencing the parameters essential for practical applications, from the areas of micromechatronics and microelectronics.

Electric-field control of the ferro-paraelectric phase transition in Cu:KTN crystals

We report an efficient approach for ferro-paraelectric phase transition control in Cu:KTN crystals by using AC electric fields. Based on a dielectric loss mechanism, the thermal effect is induced directly inside the crystal without using extra thermal sources or complicated thermostat systems. By adjusting either the amplitude or the frequency of an AC electric field, we can easily and precisely control the ferro-paraelectric phase transition process which concurs with dynamic development of polar nanostructures of KTN crystals. In addition, we use a laser beam to probe in real time the dynamic process of crystalline phase transition. The study is important for developing novel electro-optic and ferroelectric devices for a wide range of photonic applications.

A tetragonal tungsten bronze-type photocatalyst: Ferro-paraelectric phase transition and photocatalysis

Although ferroelectrics have potential applications in photocatalysis due to their highly efficient charge separation, their mechanism of charge separation is still unknown. A ferroelectric Sr0.7Ba0.3Nb2O6 (SBN-70) semiconductor with a low ferro-paraelectric phase transition (65 °C) was studied. The photocatalytic activity for H2 production by ferroelectric and paraelectric SBN-70 was examined. The spontaneous polarization in the ferroelectric phase strongly affected the photocatalytic performance and parallel ferroelectric domains significantly promoted photogenerated charge separation to result in better photocatalytic H2 production. This knowledge provides an important basis for the fabrication of ferroelectric photocatalysts with improved charge separation ability.

Crystal structure, magnetic, thermal behavior, and spectroscopic studies of two new bimetallic hydrogenselenites: [Cu2−xNix (HSeO3)2Cl2.4H2O], (x = 0.62; 0.91)

Two new iso-structural bimetallic hydrogenselenites [Cu2−xNix(HSeO3)2Cl2.4H2O] (x = 0.62; 0.91) have been synthesized from solution and characterized by single-crystal and powder X-ray diffraction. They crystallized in the orthorhombic Pnma space group with the following lattice parameters: for Cu1.09Ni0.91(HSeO3)2Cl2.4H2O: a = 9.0931 (2) Å, b = 17.7717 (4) Å, c = 7.1620 (2) Å, Z = 4, and for Cu1.38Ni0.62(HSeO3)2Cl2.4H2O: a = 9.0931 (4) Å, b = 17.7467 (7) Å, c = 7.1717 (3) Å; Z = 4. The crystal structure of this compound consists by a three-dimensional framework, but it may be described as a bi-dimensional structure consisting of layers, parallel to the (010) plane formed by two types of (Cu/Ni) octahedral and (HSeO3)− trigonal pyramids. The magnetic measurement, thermal and spectroscopic studies were performed for these compounds. The magnetic results reveal the appearance of a weak ferromagnetic behavior at low temperature (Tc = 16 K for x = 0.91 and 18.8 K for x = 0.62). The DSC analysis enabled us to locate two endothermic peaks. The first peak can be attributed to a completely dehydration of the material, in this transformation, the compounds undergo a structural phase transition which can favor a non-centrosymmetric phase at high temperature confirmed by the thermodiffractograms measurement. The second peak for these samples is due to the ferro-paraelectric phase transition which can be explained by an order– disorder transition.

Photothermoelectric (PTE) Versus Photopyroelectric (PPE) Detection of Phase Transitions

The photopyroelectric (PPE) technique is one of the photothermal (PT) methods mostly used for phase transitions investigations. In this paper, we want to compare the PPE results with those obtained using another, recently developed PT method [the photothermoelectric (PTE) calorimetry] for the same purpose of detecting phase transitions. The well-known ferro-paraelectric phase transition of TGS, taking place at a convenient temperature (about \(49\, {}^{\circ }\hbox {C}\)), has been selected for demonstration. A comparison of the two PPE and PTE methods, both in the back detection configuration (in the special case of optically opaque sample and thermally thick regime for both sensors and sample) shows that they are equally suitable for phase transitions detection. Performing a proper calibration, the amplitude and phase of the signals can be used in order to obtain the critical behaviour of all sample’s static and dynamic thermal parameters.

Photothermoelectric (PTE) detection of phase transitions. Application to triglycinesulphate (TGS)

A recently introduced photothermal method, the photothermoelectric (PTE) calorimetry is proposed for the first time in order to detect phase transitions. The capability of both back (BPTE) and front (FPTE) detection configurations in detecting phase transitions is analyzed. It was found that the back detection configuration, with optically opaque sample and thermally thick sample and TE sensor, is very suitable for phase transitions detection; the information, in this configuration, can be collected from both amplitude and phase of the BPTE signal and the amplitude has the possibility of amplifying the critical anomaly of the thermal parameters. In the FPTE configuration, the information about phase transition is contained only in the amplitude of the signal. Using the PTE method, the well-known ferro-paraelectric phase transition of triglycinesulphate (TGS), tacking place at about 49°C, was investigated. Comparison with the photopyroelectric (PPE) method is performed.

Influence of diffuse phase transition on the anelastic behavior of Nb-doped Pb(Zr0.53Ti0.47)O3 ceramics

In this study, we investigated the possible physical mechanisms giving rising to thermally activated anelastic relaxations in Nb-doped Pb(Zr0.53Ti0.47)O3 ceramics, at temperatures below the ferro-paraelectric phase transition. The dielectric analysis showed a ferro-paraelectric diffuse phase transition, extended over a wide temperature range, but without relaxor behavior. From the anelastic measurements, three regions with anomalies were identified. The mechanisms involved with anomalies between 300–570 K had been previously investigated for Pb(ZrxTi1−x)O3-based materials. However, the responsible mechanisms by the other anelastic relaxation peak, at 596 K, are controversial. The results and analysis described here show that this peak can be related to the freezing of the polar regions or to the strong pinning of ferroelectric clusters and domains, which are responsible for the observed diffuse phase transition in this ferroelectric material.

Synthesis and physical properties of Ca- and Ta-modified (K,Na)NbO3 lead-free piezoelectric ceramics

Polycrystalline samples of lead-free Ca and Ta co-substituted potassium sodium niobate (K0.5Na0.5NbO3, KNN) ceramics have been prepared by solid state reaction technique. X-ray diffraction showed formation of a single-phase perovskite structure with orthorhombic symmetry. Substitution inhibits the grain growth, improves densification and decreases the ferro-paraelectric phase transition temperature. Temperature dependent dielectric permittivity studies demonstrate significant decrease in peak-permittivity values in the substituted samples. Bulk longitudinal piezoelectric coefficient is significantly enhanced, up to ∼155 pC/N for (K0.48Na0.48Ca0.02)(Nb0.85Ta0.15O3) as compared to 95 pC/N for pristine KNN ceramic. Local piezoelectric properties have been observed by piezoresponse force microscopy (PFM) technique. Distinct piezocontrast was studied in both vertical and in-plane modes of PFM for all samples. The samples exhibit self-polarization effect in the unpoled state and effective local vertical piezoelectric coefficient was the largest in Ca and Ta co-substituted sample whereas the in-plane piezoelectric coefficient was maximum for Ca-substituted KNN sample. These studies are important for using substituted lead free KNN materials in various piezoelectric applications.

The strong influence of iron additions on the lead–lanthanum–titanate ceramics

In the present work, phase transitions and electrical characteristics of iron and lanthanum substituted lead titanate are reported. Structural analysis of the prepared samples was carried out to confirm the formation of the compounds in the proper phase. The average grain size was estimated using Scherrer’s equation. Dielectric properties of the samples have been studied as functions of temperature and frequency. Variations of the dielectric constant (εr) as function of temperature show a diffuse ferro-paraelectric phase transition. The diffusivity and the relaxation strength were estimated using the modified Uchino-law, and the relaxation time of these materials satisfies the Vogel–Fulcher equation.

The p–T phase diagram for new ferroelectric bis-thiourea pyridinium bromide

The effects of temperature and pressure on physical properties of the ferroelectric inclusion compound bis-thiourea pyridinium bromide were studied by dielectric spectroscopy, neutron and X-ray diffractometry and nuclear magnetic resonance (NMR). The results permitted a construction of the p–T phase diagram for this compound. At ambient pressure bis-thiourea pyridinium bromide exists in three phases and the ferro-ferroelectric phase transition observed at T2=150K is discontinuous in contrast to the ferro-paraelectric phase transition observed at T1=180K. The application of pressure of about 800MPa at room temperature and then cooling of this compound to below T=160K induces the appearance of a new phase (IV).

Orientation-dependent phase transition and dielectric properties of Ba0.85Ca0.15Ti0.9Zr0.1O3 thin films

Polycrystalline Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) thin films with (100) preferential and random orientation are prepared on the LaNiO3 electrodes coated on Si substrates by chemical solution deposition process. The results show that the two types of films stabilize in the pure perovskite structure. The ferro-paraelectric phase transitions of two types of films occur at the temperature ranges of 280.2-297.8 K and 278.4-287.6 K, respectively. The dielectric constant, relaxation time and tunability of the random orientation film are smaller than those of the (100) preferential film but both almost have the similar leakage current characteristics. The mechanism associated with the change of the electrical properties of the thin films is also discussed.