Ferroelectric-paraelectric Phase Transition Temperature Research Articles

First-principles study of non-linear thermal expansion in cadmium titanate by molecular dynamics incorporating nuclear quantum effects

First-principles molecular dynamics (FPMD) simulations were applied for analyzing structural evolutions around the paraelectric-ferroelectric phase transition temperature in the perovskite-type cadmium titanate, CdTiO3. Since the phase transition is reported to occur at the low temperature around 80 K, the quantum thermal bath (QTB) method was utilized in this study, which incorporates the nuclear quantum effects (NQEs). The structural evolutions in the QTB-FPMD simulations are in reasonable agreement with the experimental results, by contrast in the conventional FPMD simulations using the classical thermal bath (CTB-FPMD). Especially, the non-linear thermal expansion of lattice constants around the phase transition temperature was well reproduced in the QTB-FPMD with the NQEs. Thus, the NQEs are of importance in phase transitions at low temperatures, particularly below the room temperature, and the QTB is useful in that it incorporates the NQEs in MD simulations with low computational costs comparable to the conventional CTB.

Large tensile-strained BaTiO3 films grown on a lattice-mismatched La-doped BaSnO3 bottom electrode

A tensile strain of 2% was achieved in BaTiO3 films using La-doped BaSnO3 bottom electrodes. The ferroelectric-paraelectric phase transition temperature exceeds 400 °C.

Improved electromechanical properties of Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 ferroelectric ceramics via Sm-modification

Sm-modification has recently attracted widespread attention as an optimized method for enhancing the electromechanical properties of Pb-based perovskite ferroelectrics. The present study extends the application of Sm-modification to the Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 (PNN-PZT) ceramics, aiming to improve their electromechanical properties. The impact of Sm-doping on the phase structure, microstructure, domain morphology, dielectric and piezoelectric properties was comprehensively investigated. The results demonstrate that the Sm-doping enhances the dielectric and piezoelectric properties while retaining competitive ferroelectric-paraelectric phase transition temperature (Tm). Notably, for the 2 mol% Sm-doped samples, a significant piezoelectric coefficient d33 of 1130 pC/N and a high Tm of 130 °C were achieved, accompanied by an improved dielectric constant (εr) and electromechanical coupling factor (kp). The comprehensive properties of Sm-doped PNN-PZT ceramics exceed the general trend observed in current Pb-based ferroelectric ceramics. This research confirms the effectiveness of the Sm-modification method in PNN-PZT systems, establishing it as a promising candidate for high-performance electromechanical applications.

Tuning electrical properties of BaTiO3 with iron modification

BaTiO3 plays an important role in advanced functional devices owing to its fascinating properties. Though it is an excellent ferroelectric material, its magnetism can be switchable via suitable modification. In this report, we have studied iron-modified BaTiO3, which has been prepared using cost-effective high-temperature solid-state reaction techniques. The Fe-modified BaTiO3 maintains its crystallinity in the tetragonal phase with P4mm space group with a slight variation of tetragonality ratio to 1.002 from 1.008 of BaTiO3 of the identical synthesis method. This is confirmed by Rietveld refinement. Field emission scanning electron microscopy (FESEM) and EDX (energy dispersive X-rays) spectrum along with an elemental mapping analysis has provided the feature of the Fe-modifed BaTiO3. Atomic force microscope (AFM) has been employed to get the detailed surface topology (2D and 3D) and surface roughness of the developed systems. This deformation caused by the incorporation of Fe significantly modifies the electrical properties of barium titanate. The ferroelectric-paraelectric phase transition temperature (Tc) of Fe-modified BaTiO3 has been diffused and shifted to 300 °C from 120 °C of pure BaTiO3, suggesting the materials for the high-temperature capacitive application. The room temperature M-H hysteresis of Fe-modified BaTiO3 indicates the ferromagnetism developed in the BaTiO3 with the introduction of Fe. The ac conductivity is in the order of 10−4 Ω−1cm−1, and its frequency response obeys Jonscher's power law. Different charge carriers are responsible for diverse conduction processes in different temperature ranges confirmed by the Arrhenius plot. Impedance spectroscopy studies reveal the existence of NTCR characteristics of the developed system. Well defined ferroelectric hysteresis loop indicates the existence of ferroelectricity in the developed system. The analysis of various electrical parameters has provided information on the material's dielectric relaxation and conduction mechanisms for possible application in functional devices.

Phase transition and energy storage properties of Bi0.5Na0.5TiO3–Bi(Mg2/3Nb1/3)O3 lead-free ceramics

Bi0.5Na0.5TiO3 (BNT) lead-free ceramics have been extensively studied due to their excellent dielectric, piezoelectric and ferroelectric properties. The phase structure and functionalities of BNT can be feasibly adjusted by doping/forming solid solutions with other elements/components. In this work, Bi(Mg2/3Nb1/3)O3 (BMN) was introduced into BNT by a conventional solid-state reaction to form a homogeneous solid solution of (1-x)(Bi0.5Na0.5)TiO3-xBi(Mg2/3Nb1/3)O3 (BNT-xBMN) with a perovskite structure. With the increase of BMN content, a phase transition from rhombohedral R3c to tetragonal P4bm has been confirmed by XRD, along with shifting the ferroelectric-paraelectric phase transition temperature to lower temperatures with broadening dielectric peaks. Furthermore, an optimized recoverable energy density of 1.405 J/cm3 was achieved for BNT-0.10BMN ceramics under a low applied electric field of 140 kV/cm, which is mainly attributed to the transformation from ferroelectric to ergodic relaxor phase.

Sn2P2S6: A lead-free reversible thermochromic ferroelectric with high near-infrared reflectance

Multifunctional thermochromic materials integrated optical, ferroelectric, and/or magnetic properties have been long envisioned and played an invaluable role in signal processing and non-contact optical information storage in smart windows. However, poor materials stability, together with high discoloration temperature, absence of ferroelectric, or magnetic behaviors, impedes most thermochromic materials for practical applications. Here, the thermochromic behavior of all-inorganic lead-free ferroelectric Sn2P2S6 (SPS) is extensively studied, which exhibits a reversible color change between light orange and red around the ferroelectric-paraelectric phase transition temperature (∼ 67 °C). In situ powder X-ray diffraction (PXRD) and Raman spectroscopy indicate the change of P-S and Sn-S bond distance, and thus result in the modification of (P2S6) octahedral geometry and the coordination environment of Sn2+ ions along with the evolution of thermochromism (TCM). Additionally, the first-principles calculations reveal that, the Sn 5s2 stereochemically active lone pair electrons evoke negative lattice expansion comparable to that of the known ZrW2O8 at warming and is responsible for the reversible TCM of SPS. SPS also possesses high near-infrared reflectance (R > 80 %, 1100-2500 nm). The integration of ferroelectricity, high near-infrared reflectance, and TCM below 100 °C renders potential applications of the titled compound in multifunctional optical smart windows.

Phase transition and ferroelectric properties study of lead-free 0.95BaTiO3-0.05CaSnO3 ceramics synthesized by high energy ball milling assisted solid state reaction route

Lead-free 0.95BaTiO3-0.05CaSnO3 ceramics were synthesized by high energy ball milling (HEBM) assisted solid state reaction route. Calcination temperature and time for phase formation was optimized and found to be relatively less than other BaTiO3-doped system. X-ray diffraction (XRD) and Raman study were performed for phase examination of the synthesized material. Rietveld analysis confirmed double-phase co-existence of this 95/05 system at room temperature. Sintering temperature and time for better densification were optimized to be 1250°C for 3hr. From dielectric study it was found that ferroelectric-paraelectric phase transition temperature(Tc, observed≈ 55°C) was reduced considerably in compared to the pure BaTiO3 system (Tc≈ 125°C). No relaxorbehaviour was found from dielectric study. Polarization vs. electric field hysteresis loop study showed the development of saturated hysteresis loops but the remnant polarization was found decreased compared to pure BaTiO3 system.

Phase transitions and electrocaloric effects of (111)-oriented K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> epitaxial films: effect of external stress and misfit strains

Lead-free K<sub>1–<i>x</i></sub>Na<sub><i>x</i></sub>NbO<sub>3</sub> thin films, as a candidate for sensors and electromechanical and electrocaloric cooling devices, have increasingly received attention. However, for (111)-oriented films, the relation between phase transitions and electrocaloric effect is not clear. Here, we derive the thermodynamic potential of (111)-oriented thin film ferroelectrics K<sub>1–<i>x</i></sub>Na<sub><i>x</i></sub>NbO<sub>3</sub> based on the 8<sup>th</sup> order polynomial function, and then establish the temperature-misfit strain and out-of-plane stress-in-plane misfit strain phase diagrams and calculate electrocaloric (EC) entropy changes Δ<i>S</i> and temperature changes Δ<i>T</i>. This study focuses on mechanical and orientation controls of room-temperature EC effect of K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> films, which is critical for environmentally friendly electrocaloric refrigeration applications in practice. Under the stress-free and zero misfit strain conditions, the (111)-oriented K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> film in an electric field of 30 MV/m has a maximum EC Δ<i>T</i> of ～18 K near the rhombohedral ferroelectric-paraelectric phase transition temperature (about 673 K). However, an out-of-plane stress of about –6.7GPa can reduce the optimal operating temperature to room temperature where the K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> film has the EC Δ<i>T</i> of ～7.5 K under the action of applied electric field of 30 MV/m. The present work provides theoretical guidance for exploring the strain engineering and orientation engineering of K<sub>1–<i>x</i></sub>Na<sub><i>x</i></sub>NbO<sub>3</sub>-based thin films with optimized electrocaloric and electromechanical properties.

Exploring the electromechanical response and electric field-induced dielectric anomalies in PMN–PT electroceramics

Electromechanical and dielectric properties of PMN–PT ferroelectric ceramics are investigated. In particular, dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency. Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves, [Formula: see text], which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature. A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90[Formula: see text] and 180[Formula: see text] domains walls.

Core-Shell Structure and Dielectric Properties of Ba0.6Sr0.4TiO3@ Fe2O3 Ceramics Prepared by Co-Precipitation Method

Ba0.6Sr0.4TiO3 (BST) ceramic materials have been widely used in the field of multilayer ceramic capacitors. Surface modification through the surface coating to form a heterogeneous layer could effectively improve the dielectric properties. In this work, BST powders were prepared by a co-precipitation method. The effects of reaction conditions on the microstructure of the BST powder were investigated. The reaction temperatures significantly affected the morphology of BST powder, and the rhombic-type particles were obtained with the reaction temperature around 80 °C. Meanwhile, the BST@Fe2O3 was prepared by the chemical precipitation method using BST powders with rhombic-type microstructure as “core”, and the so-called “core-shell” microstructure was confirmed in the BST@Fe2O3 powder. Then, BST@x wt%Fe2O3 (x = 2.5, 5, 7.5, and 10, denoting the different content of Fe2O3) ceramics were further prepared, and the influence of “core-shell” structure on the phase structure, microstructure, and dielectric properties was investigated. With the increasing of Fe2O3 content, the ferroelectric–paraelectric phase transition temperature shifts toward lower temperatures, and dielectric peaks gradually become broad and frequency-dependent, which may be due to inconsistent chemical composition from core to shell.

Anomalous changes in the acoustic properties and central peak behaviors of PbxBa1−xNb2O6 single crystals with x = 0.5 studied by Brillouin spectroscopy

The acoustic properties of tetragonal PbxBa1−xNb2O6 (PBN-x) single crystals with x = 0.5 were studied by Brillouin spectroscopy over a wide temperature range from room temperature to 600 °C. Anomalous changes in the Brillouin frequency shift and the half width of acoustic waves were observed at ∼350 °C that corresponds to the ferroelectric–paraelectric phase transition temperature of PBN-0.50. The longitudinal sound velocity and its associated elastic constant (C33) showed substantial softening in the paraelectric phase when the phonon propagated along the polar c axis, while their degree of softening for the phonon along the a axis was small, revealing clear acoustic anisotropy. It was associated with the strong polarization dependence of the quasi-elastic central peak. The relaxation time derived from the central peak seemed to follow the critical slowing-down behavior indicating order–disorder nature of the phase transition. Among C44 and C66, the former displayed substantial softening in the ferroelectric phase resembling the order parameter behavior. The longitudinal sound velocity and the related acoustic damping showed significant anomalies in the ferroelectric phase of unpoled PBN-0.5, which disappeared completely under poled condition. The possible origin for these unexpected acoustic anomalies was suggested.

Dielectric properties and relaxor ferroelectric behavior of (1–y)Ba(Zr0.1Ti0.9)O3–yBa(Zn1/3Nb2/3)O3 ceramics

Abstract The microstructure, dielectric and ferroelectric properties of (1–y)Ba(Zr0.1Ti0.9)O3–yBa(Zn1/3Nb2/3)O3 (y=0–0.05) ceramics prepared by traditional solid state method were investigated by X-ray diffractometer, scanning electron microscope, electric parameter testing system and ferroelectric tester. It is found that the barium zirconate titanate based ceramics are single-phase perovskites as y increases up to 0.05 and their average grain size decreases with the increase of y. The permittivity maximum er,max is suppressed from 8948 to 1611 at 1 kHz with increasing y, and the ferroelectric–paraelectric phase transition temperature Tm decreases from 93 to –89 °C at 1 kHz as y increases. The composition-induced diffuse phase transition is enhanced with increasing y. The relaxor-like ferroelectric behavior with a strong frequency dispersion of Tm and permittivity at T

Non-contact localized probing of ferroelectric phase transitions in Li+/Er3+:BaTiO3 ceramics using fluorescence abnormalities

Fluorescence abnormalities associated with the ferroelectric phase transition of Li+/Er3+:BaTiO3 (BLET) ceramics were studied based on photoluminescence (PL) spectra. Sharp changes were found in the integrated intensities, peak intensities, and fluorescence intensity ratios of both upconversion spectra (2H11/2/4S3/2−4I15/2) and downconversion infrared spectra (4I13/2−4I15/2) around the ferroelectric-paraelectric phase transition temperature in BLET ceramics under the excitation of a 980 nm laser. All changes happened within the temperature interval of 126 °C–130 °C. The relative changing rate (RCR) was adopted to quantitatively describe this structure-sensitive PL. For the system under study, the maximum RCR occurs for the PL peak intensity at 542.7 nm.

Enhanced piezoelectric properties of Mn‐modified Bi5Ti3FeO15 for high‐temperature applications

AbstractBi5Ti3FeO15 (BTF) has recently attracted considerable interest as a typical multiferroic oxide, wherein ferroelectric and magnetic orders coexist. The ferroelectric order of BTF implies its piezoelectricity, because a ferroelectric must be a piezoelectric. However, no extensive studies have been carried out on the piezoelectric properties of BTF. Considering its high ferroelectric‐paraelectric phase transition temperature (Tc ~ 761°C), it is necessary to analyze the piezoelectricity and thermal stabilities of BTF, a promising high‐temperature piezoelectric material. In this study, lightly manganese‐modified BTF polycrystalline oxides are fabricated by substituting manganese ions into Fe3+ sites via the conventional solid‐state reaction method. X‐ray diffraction and Raman spectroscopy analyses reveal that the resultant manganese‐modified BTF has an Aurivillius‐type structure with m = 4, and that the substitutions of Fe by Mn lead to a distortion of BO6. The temperature‐dependent dielectric properties and direct‐current (DC) resistivity measurements indicate that the Mn ions can significantly reduce the dielectric loss tanδ and increase the DC resistivity. The piezoelectricity of BTF is confirmed by piezoelectric constant d33 measurements; it exhibits a piezoelectric constant d33 of 7 pC/N. Remarkably, BTF with 4 mol% of Mn (BTF‐4Mn) exhibits a large d33 of 23 pC/N, three times that of unmodified BTF, whereas the Curie temperature Tc is almost unchanged, ~765°C. The increased piezoelectric performance can be attributed to the crystal lattice distortion, decreased dielectric loss tanδ, and increased DC resistivity. Additionally, BTF‐4Mn exhibits good thermal stabilities of the electromechanical coupling characteristics, which demonstrates that manganese‐modified BTF oxides are promising materials for the use in high‐temperature piezoelectric sensors.

Magnetoelectricity of barium titanate/cobalt ferrite nanoparticles incorporated into poly(vinylidene fluoride-co-trifluoroethylene) copolymer films

Incorporating ferroelectric and ferromagnetic nanoparticles into copolymers can produce composites with novel properties for broad applications especially in electronics. In this research, nanoparticles of barium titanate (BTO) and cobalt iron oxide (CFO) were chemically synthesised and then individually incorporated in poly(vinylidene fluoride-co-trifluoroethylene) to form multi-layered magnetoelectric film. BTO-P(VDF-TrFE)/CFO-P(VDF-TrFE)/BTO-P(VDF-TrFE) sandwich type films - (20-30 μm in thickness each) - were synthesised using a home-made simple mould casting and blending techniques. The addition of BTO and CFO nanoparticles to the polymer enhanced the dielectric constant, but lowered the ferroelectric-paraelectric phase transition temperature of the P(VDF-TrFE). For the sandwich type film, a maximum value of direct out of plane magnetoelectric coupling coefficient (α33) 145 mV/cm·Oe was measured at ambient temperature. For such structure, the perfect isolating condition of the cobalt ferrite piezomagnetic phase and the proper contact and bonding between the piezoelectric and magnetostrictive phases enhanced the magnetoelectric effect. The fabricated film could be a potential candidate for magnetoelectric devices and sensor applications.

Enhanced ferroelectric relaxor behavior of Ho2O3-modified barium zirconate titanate ceramics

Ho2O3 doped Ba(Zr0.1Ti0.9)O3 ceramics were prepared by conventional solid state reaction route and their microstructure, dielectric properties and ferroelectric properties were investigated with the variation of Ho2O3 content using X-ray diffraction, scanning electron microscope, LCR measuring system and ferroelectric tester. It is found that the Ho3+ ions initially substitute the B-site host ions maintaining the perovskite structure in Ba(Zr0.1Ti0.9)O3 ceramics and then contribute to the formation of secondary phase with the continuous increase of Ho2O3 content. The average grain size decreases significantly as the Ho2O3 concentration increases. The ferroelectric-paraelectric phase transition temperature Tm of Ba(Zr0.1Ti0.9)O3 ceramics decreases with increasing Ho2O3 content. Based on the increase of critical exponent γ from the modified Curie–Weiss equation as well as the increase of deviation from Curie–Weiss law, the diffuse phase transition behavior is enhanced with increasing Ho2O3 content, indicating a composition-induced diffuse transition. A normal ferroelectric behavior with diffuse phase transition is obtained for the undoped Ba(Zr0.1Ti0.9)O3 ceramics. However, the relaxor-like ferroelectric behavior with a strong frequency dispersion of relative permittivity maximum ermax at T < Tm and a strong diffuse phase transition is found for Ba(Zr0.1Ti0.9)O3 ceramics with high Ho2O3 content. The high Ho2O3 content ceramics obey the empirical Vogel–Fulcher relation, which confirms the relaxor behavior of Ba(Zr0.1Ti0.9)O3 ceramics with high Ho2O3 content. The remnant polarization increases and then decreases with the increasing Ho2O3 content while the coercive field decreases with the increase of Ho2O3 content in Ba(Zr0.1Ti0.9)O3 ceramics.

The Structure, Dielectric, and Optical Properties of c-Oriented SBN-50 Films Grown on Pt/Al2O3 Substrate

Studies of the structure, dielectric and optical properties of thin films of a relaxor ferroelectric Ba0.5Sr0.5Nb2O6 grown on Pt(111)/Al2O3 (c-cut) substrate by high-frequency RF-sputtering in oxygen atmosphere, were performed. X-ray diffraction studies showed that Ba0.5Sr0.5Nb2O6 films are c-oriented. The unit cell parameters in the tetragonal approximation were c = 3.949(1) A and a = 12.38(1) A. It was established that the ferroelectric–paraelectric phase-transition temperature rises and optical anisotropy increases in the object in comparison with the bulk material. Reasons for the elucidated regularities are discussed.

Структура, диэлектрические и оптические свойства c-ориентированных пленок SBN-50, выращенных на подложке Pt/Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

AbstractStudies of the structure, dielectric and optical properties of thin films of a relaxor ferroelectric Ba_0.5Sr_0.5Nb_2O_6 grown on Pt(111)/Al_2O_3 (c-cut) substrate by high-frequency RF-sputtering in oxygen atmosphere, were performed. X-ray diffraction studies showed that Ba_0.5Sr_0.5Nb_2O_6 films are c-oriented. The unit cell parameters in the tetragonal approximation were c = 3.949(1) Å and a = 12.38(1) Å. It was established that the ferroelectric–paraelectric phase-transition temperature rises and optical anisotropy increases in the object in comparison with the bulk material. Reasons for the elucidated regularities are discussed.

Piezoelectric/photoluminescence effect in one-dimensional lead-free nanofibers

In present work, a multifunctional piezoelectric/photoluminescence effect, which originated from the combination of the piezoelectric properties and the photoluminescence effect, was realized in one-dimensional Er3+ doped lead-free BaTiO3 nanofibers prepared by a sol-gel based electrospinning method. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) were utilized to characterize the morphologies and phase structures. The effect of the host crystallization and rare-earth concentration on the structure and photoluminescence properties was studied. In addition, temperature-dependent PL spectrum exhibited a piezoelectric/photoluminescence coupling effect, characterized by the enhanced photoluminescence intensity around the ferroelectric-paraelectric phase transition temperature of BaTiO3.

Improved piezoelectric and electro-caloric effects in the BaTi0.975(Nb0.5Yb0.5)0.025O3 lead-free ceramic characterized by phase-coexistence at room temperature

A lead-free BaTi0.975(Nb0.5Yb0.5)0.025O3 (BTYN25) ceramic sample was prepared using a solid state reaction method. The polymorphic phase transition (PPT) from the orthorhombic to the tetragonal phase (O-T) at room temperature (RT) was identified in this composition. An X-ray diffraction (XRD) study allowed the identification of those two structures at RT. Dielectric measurements made it possible to determine the phase transitions. The Raman study confirmed the structures and the phase transitions. A good piezoelectric coefficient of d33 = 140 pC/N, a planar electromechanical coupling factor of kp = 29% and a remanent polarization of Pr = 10.8 μC/cm2 were obtained. The electro-caloric effect (ECE) was investigated by using two different methods: an indirect method with hysteresis loops and a direct method with a modified Differential Scanning Calorimeter (DSC). A good electro-caloric strength (ξ = ΔT/ΔE) of ξ = 0.17 °C mm/kV near the ferroelectric-paraelectric phase transition temperature was obtained. At RT, a significant electro-caloric strength of ξ= 0.05 °C mm/kV was found due to the coexistence of the two phases: the orthorhombic one and the tetragonal one. A good agreement between the two methods was found. These values are very interesting when compared to those for other materials and show the possibility of using such lead-free ceramics for electro-caloric applications.