Ferroelectric Phase Transition Temperature Research Articles

Temperature-dependent Raman spectra and electrical properties of 0.69Pb(Mg1/3Nb2/3)O3–0.31PbTiO3 single crystals

The temperature-dependent Raman spectra and electrical properties of the 0.69Pb(Mg1/3Nb2/3)O3–0.31PbTiO3 (0.69PMN–0.31PT) single crystals were investigated. Based on the group theory, the poled 0.69PMN–0.31PT single crystals belong to the monoclinic crystal system, which was confirmed by the room-temperature Raman spectra. The 0.69PMN–0.31PT single crystals experience successive structural phase transitions, i.e., a monoclinic–tetragonal (FEM–FET) phase transition at TM–T and a tetragonal–cubic (FET–PC) phase transition at T m determined by the dielectric measurement. Due to the enhancement of long-range order, their FEM–FET phase transition becomes more obvious after the poling process. The wavenumbers and line widths of the 271, 502, 575, 795 cm−1 Raman modes, and the intensity ratios of $$ I_{{271{\text{cm}}^{ - 1} }} /I_{{795{\text{cm}}^{ - 1} }} $$ and $$ I_{{502{\text{cm}}^{ - 1} }} /I_{{575{\text{cm}}^{ - 1} }} $$ exhibit obvious anomalies around T M–T and T m, which are closely related to the FEM–FET and FET–PC phase transitions. The temperature and electric field (E)-induced phase transitions are observed in the unipolar strain–E (S–E) curves. The converse piezoelectric constant (d 33), maximum strain value (S max%) and longitudinal electrostrictive coefficient (Q) increase considerably around the ferroelectric phase transition temperature T M–T.

Ferroelectric domain freezing and charge conduction in proton-irradiated K(H0.36D0.64)2PO4

We have studied the effects of proton irradiation in K(H0.36D0.64)2PO4 single crystals by employing impedance spectroscopy. Frequency-dependent dielectric loss measurements allowed us to investigate changes in the domain wall dynamics of a proton-irradiated crystal with a ferroelectric phase transition temperature raised by 5 K. Thus, the increase caused by proton irradiation in the activation energy of the domain freezing in the direction of the hydrogen bonds was found to be significantly greater than in the case of KH2PO4. Furthermore, the temperature dependence of the power-law exponent n in the frequency-dependent electrical conductivity in the proton-conducting systems manifested changes arising from the proton irradiation in the interactions between the mobile ionic (proton) charges and their environments.

Raman spectroscopy of proton-irradiated K(H1−xDx)2PO4

We have employed Raman spectroscopy in order to study the mechanism of the significantly increased ferroelectric phase transition temperatures in proton-irradiated K(H1−x Dx)2PO4 crystals. Prominent changes occurred in the asymmetric stretching vibration mode frequency of D2PO4 molecules in the proton-irradiated crystals, thus stating the role of the lattice coupled to H/D.

Diffused phase transition of Ba1−x Eu x TiO3 ceramics

By applying the sol-gel method, we fabricated Ba1−x Eu x TiO3 (BET) ceramics as a single peroveskite phase in the composition range of x = 0 ~ 0.20. The BET ceramics displayed a ferroelectric phase transition temperature that changed from 120 ◦C to 80 ◦C, and exhibited the coexistance of the tetragonal, and cubic structures as the Eu composition was increased. They also displayed anomalous dielectric behaviors related to structural relaxation in the temperature range from 200 ◦C to 600 ◦C. We considered the Arrhenius temperature dependence of the dielectric relaxation time by using the electric modulus formalism. The characteristic activation energy was thought to be related with the substitution of Eu (Eu2+, Eu3+) ions for Ba2+ or Ti4+ ions in the perovskite structure.

Surface and finite size effects impact on the phase diagrams, polar, and dielectric properties of (Sr,Bi)Ta2O9 ferroelectric nanoparticles

In the framework of the thermodynamic approach Landau-Ginzburg-Devonshire (LGD) combined with the equations of electrostatics, we investigated the effect of polarization surface screening on finite size effects of the phase diagrams, polar, and dielectric properties of ferroelectric nanoparticles of different shapes. We obtained and analyzed the analytical results for the dependences of the ferroelectric phase transition temperature, critical size, spontaneous polarization, and thermodynamic coercive field on the shape and size of the nanoparticles. The pronounced size effect of these characteristics on the scaling parameter, the ratio of the particle characteristic size to the length of the surface screening, was revealed. Also our modeling predicts a significant impact of the flexo-chemical effect (that is a joint action of flexoelectric effect and chemical pressure) on the temperature of phase transition, polar, and dielectric properties of nanoparticles when their chemical composition deviates from the stoichiometric one. We showed on the example of the stoichiometric nanosized SrBi2Ta2O9 particles that except the vicinity of the critical size, where the system splitting into domains has an important role, results of analytical calculation of the spontaneous polarization have a little difference from the numerical ones. We revealed a strong impact of the flexo-chemical effect on the phase transition temperature, polar, and dielectric properties of SryBi2+xTa2O9 nanoparticles when the ratio Sr/Bi deviates from the stoichiometric value of 0.5 within the range from 0.35 to 0.65. From the analysis of experimental data, we derived the parameters of the theory, namely, the coefficients of expansion of the LGD functional, the contribution of flexo-chemical effect, and the length of the surface screening.

Improved Thermal Stability of Ferroelectric Phase in Epitaxially Grown P(VDF-TrFE) Thin Films

In recent years ferroelectric polymers have attracted much attention due to their potentials in flexible electronics. To satisfy the requirements of low operation voltage and low power consumption, it is required to reduce the ferroelectric film thickness down to, for example, 100 nm. However, decreased film thickness results in low crystallinity and thus worse electrical performance. One possible solution is to realize the epitaxial growth of ferroelectric thin films via effective control of structure and orientation of ferroelectric crystals. Here we report our work on poly(tetrafluoroethylene)-template-induced ordered growth of ferroelectric thin films. We focus on the study of thermal stability of ferroelectric phase in these ferroelectric films. Our work indicates that epitaxial growth effectively increases the crystallinity and the melting and ferroelectric phase transition temperatures and implies the extended application of ferroelectric devices at higher temperature.

Electron microscopy, XRD, Mossbauer and dielectric studies of Pb(Fe0.5Nb0.5)1-xSnxO3 multiferroic ceramics

ABSTRACTMultiferroic Pb(Fe0.5Nb0.5)1-xSnxO3 (x = 0.025, 0.05, 0.075, 0.10) ceramic compositions were prepared by solid state synthesis and usual sintering. XRD studies have shown a formation of the perovskite structure in all the compositions studied. However, a small amount of pyrochlore phase was detected in Sn-doped compositions with x ≥ 0.05. Scanning electron microscopy studies have shown that at the boundaries of the large grains there exist a lot of small submicron grains enriched by Sn. Concentration dependencies of the unit-cell parameter and ferroelectric phase transition temperatures also imply that solubility of Sn in PFN is limited to ≈ 5 at.%.

Internal electrical and strain fields influence on the electrical tunability of epitaxial Ba0.7Sr0.3TiO3 thin films

Perpetual demand for higher transfer speed and ever increasing miniaturization of radio and microwave telecommunication devices demands new materials with high electrical tunability. We have investigated built in electrical and strain fields' influence on the electrical tunability in Ba0.7Sr0.3TiO3 thin film hetero-system grown by pulsed laser deposition technique. We observed the built in electrical field by local piezo-force microscopy (as deflected hysteresis loops) and macroscopic impedance analysis (as asymmetric tunability curves), with the calculated 88 kV/cm built in field at room temperature. Negative −1.4% misfit strain (due to clamping by the substrate) enhanced ferroelectric phase transition temperature in Ba0.7Sr0.3TiO3 thin film by more than 300 K. Built in fields do not deteriorate functional film properties—dielectric permittivity and tunability are comparable to the best to date values observed in Ba1−xSrxTiO3 thin films.

Electromechanical properties of (Ba,Sr)(Zr,Ti)O3 ceramics

In this work, we report dielectric, piezoelectric and ferroelectric properties of perovskite Ba0.95Sr0.05ZrxTi(1−x)O3 (BSZT, x=0.05, 0.10, 0.15, 0.20) ceramics synthesized by using a solid-state reaction method. It is demonstrated that when the Zr concentration was 5at% and the sintering temperature was 1400°C, the BSZT ceramic gives the best overall electromechanical performance, including a large remnant polarization of ~ 12.1µC/cm2, large dielectric constants (εrpeak≈12,600, εrRT≈3500) and an excellent d33 value of ~355pC/N. Curie temperature of this ceramic is about ~100°C. The enhanced electromechanical properties of the BSZT ceramics as compared with Ba0.95Sr0.05TiO3 (BST) can be explained by optimization of the tolerance factor and shift of ferroelectric polymorphic phase transition temperatures (TPPT).

Complex domain structure in polycrystalline Pb(Sc0.5Nb0.5)O3

This letter provides evidence of ferroelectric domains existing in polycrystalline B-site cation disordered Pb(Sc0.5Nb0.5)O3. A complex domain structure with variations in characteristic length and morphology is observed below the relaxor–ferroelectric phase transition at ~98 °C. At room temperature the micrometer-sized wedge-like, lamellar-like and irregularly shaped domains are found. By approaching the relaxor–ferroelectric phase transition temperature, the domain structure changes; the fraction of micrometer-sized domains is progressively decreasing. Approximately 100 nm large domains, which form mottled patterns, are observed, and associated with polar nano domains as described in other relaxor materials.

Structural, magnetic and phonon properties of Cr(III)-doped perovskite metal formate framework [(CH3)2NH2][Mn(HCOO)3

We have incorporated Cr(III) into [(CH3)2NH2][Mn(HCOO)3] (DMMn) multiferroic metal organic framework (MOF). The highest concentration of Cr(III) in the synthesized samples reached 15.9mol%. The obtained samples were characterized by powder and single-crystal X-ray diffraction, DSC, magnetic susceptibility, dielectric, EPR, Raman and IR methods. These methods and the performed chemical analysis revealed that electrical charge neutrality after substitution of Cr(III) for Mn(II) is maintained by partial replacement of dimethylammonium (DMA+) cations by neutral HCOOH molecules. These changes in the chemical composition are responsible for weakening of the hydrogen bonds and decreased flexibility of the framework. This in turn leads to lowering of the ferroelectric phase transition temperature, observed around 185K for undoped DMMn and around 155K for the sample containing 3.1mol% of Cr(III), and lack of macroscopic phase transition for the samples with Cr(III) content of 8.2 and 15.9mol %. Another interesting effect observed for the studied samples is pronounced strengthening of the weak ferromagnetism of in Cr(III)-doped samples, associated with slight decrease of the ferromagnetic ordering temperature from 8.5K for DMMn to 7.0K for the sample with 15.9mol % Cr(III) content.

Investigations on Dielectric phase transition behavior of Pb(Fe0.5-xScx)Nb0.5O3 Multiferroic Ceramics

ABSTRACTPhase pure Pb[(Fe0.5-xScx)Nb0.5]O3 [x = 0 to 0.5] multiferroic relaxors have been synthesized to study the effect of Sc on dielectric phase tansition. Rietveld refinement of x-ray diffraction patterns confirm that the structure transforms from monoclinic (Cm) to rhomobohedral (R3m) at x = 0.3. Absence of low frequency dielectric response in compositions with low Sc content attributed to interfacial polarizabilty arising due to differences in conductivities of grain and grain boundary. Moreover, value of diffusivity parameter (γ) of high of Sc content compositions is near to 2, confirms relaxor charactertistic of these compositions. However, an essential feature of relaxors i.e., frequency dependent dielectric permittivity as a function of temperature is observed only in x = 0.5 composition [Pb(Sc0.5Nb0.5)O3 (PSN)]. In addition, ferroelectric phase transition temperature (Tmax) increases initially at lower Sc content (upto x ≤ 0.25), and further drops beyond x ≥ 0.3. Such behavior of Tmax in these compositions is due to the onset of B'-B" local cation ordering at x = 0.3. High temperature Raman spectra of Pb(Sc0.5Nb0.5)O3 (x = 0.5) confirm the stability of cation ordering in compositions with high Sc content well above the phase transition temperature.

Raman scattering in sodium nitrite crystals near the phase transition

Optical Raman spectra of a ferroelectric sodium nitrite crystal have been detected in a wide spectrum range at various temperatures, including the region of the ferroelectric phase transition. A manifestation of a transverse soft polar mode of the A 1(z) type responsible for the ferroelectric phase transition has been discovered in the spectrum at room temperature. This mode has been found to become overdamped even far from the ferroelectric phase transition temperature. This mode also appears as a central peak under heating. It has been found that the pseudoscalar mode of the A 2 type has the highest intensity in the Raman spectrum of sodium nitrite. The frequency corresponding to the maximum intensity of this mode in the Raman spectrum varies from 130 cm–1 at 123 K to 106 cm–1 at T = 513 K. A fair agreement of the experimental data for the A 1(z) mode with the Lyddane–Sachs–Teller relation has been established. The polariton curves for the A 1(z) polar mode and the dispersion curves for axinons has been plotted.

Phase transition and domain configuration of poled rhombohedral PIN–PZ–PMN–PT single crystals

A perovskite single crystal of the quaternary system PIN–PZ–PMN–PT, with rhombohedral (R) symmetry (3m) and a size of 10 × 10 × 6 mm3, was successfully grown by a slow cooling method, which had a high rhombohedral-to-tetragonal (T) ferroelectric (FE) phase transition temperature (TR–T = 129 °C). The introduction of In3+ and Zr4+ enhanced the repulsion intensity between Pb2+ and B-site cations in the ABO3 lattice and increased the energy difference ΔET–R, resulting in an improved FE phase transition temperature compared to the PMN–PT binary system single crystals. The evolution of domain configuration induced by both electric field and temperature was studied for the [001]C PIN–PZ–PMN–PT single crystal by using a polarized light microscope. Star porphyritic domains with short-range order before poling and stripe domains with long-range order after poling were observed, respectively, confirming the typical relaxor domain configurations of the R phase. Fine domain walls induced by temperature for the poled [001]C sample were responsible for the high piezoelectric property. Furthermore, minor ferroelectric property variations (ΔPmax < 6%, ΔPr < 10%) were observed at the temperature range from 20 °C to 140 °C, indicating the good thermal stability of the quaternary system PIN–PZ–PMN–PT single crystal.

Effect of CuO addition on magnetic and electrical properties of Sr2Bi4Ti5O18 lead-free ferroelectric ceramics

The effect of CuO addition on magnetic and electrical properties of Sr2Bi4Ti5O18 (SBT) lead-free bismuth layered structure ferroelectric ceramics have been studied and reported. Interestingly, the prepared samples exhibit multiferroic behavior with the coexistence of magnetic and ferroelectric phase transition temperature. Magnetic phase transition with Neel׳s temperature (TN) of 657K is observed at 0.75mol% of CuO added SBT ceramics, which is higher than the well known multiferroic BiFeO3 (643K) and the ferroelectric phase transition with Curie temperature (TC) of 587K is observed at 1mol% of CuO added SBT ceramics, which is relatively higher than the reported pure SBT ceramics (558K). Further, the electrical properties such as dielectric, ferroelectric, piezoelectric, leakage current density characteristics and optical properties were investigated as a function of x (x=0, 0.25, 0.5, 0.75 and 1mol%). Presence of strong magnetic super-exchange interactions in CuO and the creation of oxygen vacancies play a vital role in the enhancement of magnetic and electrical properties of CuO doped SBT ceramics. Moreover, the present results indicate that, small amount (0.25mol%) of CuO addition in SBT ceramics enhances the electrical properties significantly and vice versa, large amount (0.75mol%) of CuO addition enhances the magnetic properties. Thus, the presence of magneto-electric coupling effect was observed in CuO doped Sr2Bi4Ti5O18 ferroelectric ceramics.

Internal friction mechanisms in xMn0.4Zn0.6Fe2O4–(1–x)PbZr0.53Ti0.47O3 composites near the ferroelectric phase transition temperature

The internal friction in mixed magnetoelectric composites xMn0.4Zn0.6Fe2O4–(1‒x) PbZr0.53Ti0.47O3 (x = 0.1, 0.2, 0.4) prepared by the ceramic technology has been studied near the ferroelectric phase transition temperature at a frequency of 30 Hz. The contributions to the internal friction due to the kinetics of the phase transition and due to the interaction between the domain walls and point defects have been separated.

The effect of magnetic field on the ferroelectric phase transition in KH2PO4 nanoparticles embedded in magnetic porous glass

We have studied the effect of an external magnetic field on the ferroelectric phase transition in KH2PO4 nanoparticles embedded in macroporous magnetic glass with an average pore diameter of 50 nm. It is established that, in a magnetic field of 10 T, the ferroelectric phase transition temperature increases by approximately 6 K.

Investigation of Dielectric Relaxation Processes in Ba2NdFeNb4-xTaxO15 Ceramics

Dielectric response of Ba2NdFeNb4-xTaxO15 (x = 0.3, 0.6 and 2) solid solutions with Tetragonal Tungsten Bronze structure has been investigated by means of broadband dielectric spectroscopy in the frequency range from 20 Hz to 37 GHz. Pure Ba2NdFeNb4O15 compound displays ferroelectric behavior. Substitution of Nb5+ by Ta5+ considerably alters dielectric response of this system. Ferroelectric state was observed only for x = 0.3 compound with slightly lowered ferroelectric phase transition temperature. Further increase of x causes formation of relaxor state in these solid solutions and considerably lowers corresponding dielectric permittivity dispersion temperature region.

The Transverse Ising Model of the Ferroelectric Phase Transition in a System of Coupled Small Particles

The transverse Ising model was developed for an array of coupled ferroelectric small particles. Two contributions to exchange integral were included: dipole-dipole interaction and short-range coupling. General analytical equations were found for the ferroelectric phase transition temperature and order parameter. The equations obtained were analyzed numerically for cubic and tetragonal lattices of particles and cells. The shift of the ferroelectric phase transition temperature was considered as a function of the interparticle distance, tunneling constant, and geometry of particle arrangement.

Phase transition behavior and defect chemistry of [001]-oriented 0.15Pb(In1/2Nb1/2)O3-0.57Pb(Mg1/3Nb2/3)O3-0.28PbTiO3-Mn single crystals

The ferroelectric single crystals 0.5 mol. % Mn-doped 0.15Pb(In1/2Nb1/2)O3-0.57Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PIMNT-Mn) with rhombohedral perovskite structure were grown by a modified Bridgman method. Dielectric performance analysis reveals that the as-grown PIMNT-Mn single crystals exhibit complex dielectric behavior after polarization, in which the dielectric constant depends on frequency apparently around the ferroelectric phase transition temperatures TR-M and Tm. The temperature and electric-field induced ferroelectric phase transitions were investigated by the temperature dependent unipolar strain curves. The electric-field induced discontinuous ferroelectric phase transitions at elevated temperatures exhibit first-order like phase transition character. The converse piezoelectric constant (d33), maximum strain value (Smax%), and longitudinal electrostrictive coefficient (Q) increase considerably when the temperature approaches the ferroelectric phase transition temperatures TR-M and TM-T. The complex impedance curves (Z″-Z′) present typical semicircle shapes from 425 °C to 550 °C. The activation energy calculated by the Arrhenius law is 0.86 eV, indicating that the high-temperature conduction mechanism is dominated by the extrinsically formed oxygen vacancies.