Ferroelectric

Electronic structure calculations of cubic SrTiO3 and SrHfO3 are presented. The full-potential linear augmented-plane-wave method is used and exchange-correlation effects are treated by the local-density approximation. The tendency to ferroelectricity of both compounds is explored and compared by displacing the transition metal atom (Ti or Hf) towards one of the oxygens (001 direction). The calculations show that ferroelectricity is favored in SrTiO3 with respect to SrHfO3 and that this fact may be correlated with the degree of hybridization between transition metal d-O p bands as has been found for other related systems. Also a detailed discussion of the calculated electric field gradients is presented.

Polyurethane (PU) nanocomposites reinforced with magnetic iron oxide nanoparticles and/or dielectric barium titanate nanoparticles fabricated by the surface-initiated-polymerization approach were investigated. The polymer matrix incorporated with different nanoparticles shows different presenting status surrounding the nanoparticles, i.e., chemical bonding, physical entanglement and bulk polymer chain. The nanoparticles have a different effect on the thermal stability of the polymer nanocomposites. By embedding different functional nanoparticles, unique physical properties were observed, such as enlarged coercivity and larger dielectric constant (real permittivity). The synergistic effect of the binary nanoparticle reinforced PU nanocomposite was explored. The addition of the iron oxide nanoparticles does have some effect on the permittivity. However, little difference was observed in the magnetic properties and permeability after the introduction of the dielectric barium titanate nanoparticle into Fe 2 O 3 /PU nanocomposites. The permeability and permittivity of c-Fe 2 O 3 and BaTiO 3 nanoparticle reinforced PU nanocomposites were investigated with frequencies ranging from 10 MHz to 1 GHz. The predicted microwave properties from Bruggeman's equation were consistent with the measured data, except for the real permittivity of Fe 2 O 3 /BaTiO 3 /PU. The volume average method (VAM) usually used for fiber-reinforced composites with reinforcements in the thickness direction was applied in this nanocomposite system. The predicted real permittivity by VAM was found to be in better agreement with the measured data than that predicted by Bruggeman's equation.

Dielectric properties of apple, pear, orange, grape and pineapple juices were studied from 20 to 4500 MHz at 15-95°C. The dielectric constants e 0 of fruit juices decreased as frequency increased. The loss factors e 00 decreased with increasing frequency to a minimum between about 1000 and 3000 MHz, depending on temperature, and then increased as frequency increased. The frequency of that turning point increased, whereas the minimum e 00 decreased with increasing temperature. The e 00 values increased with increasing temperature below about 1000 MHz, and decreased with increasing temperature above 3000 MHz. Dielectric constants decreased consistently and linearly with increasing temperature. Linear or polynomial correlations for the dependence of dielectric properties on temperature were developed. The power penetration depth of all fruit juices decreased with increasing frequency. The depth decreased as temperature increased at lower frequencies and increased with temperature above 3000 MHz. The dielectric properties obtained in the study provide important parameters for juice pasteurization by dielectric heating.

The colossal piezoelectric effect of relaxor-based ferroelectrics has attracted much attention due to the technological importance of the conversion between electric and mechanical energies. The mechanism of the significant field effect on piezoelectric properties in this disordered system has become one of the current topics in pure and applied physics. The important key factor in the understanding of relaxors is polar nanoregions (PNRs) which appear at temperatures far above the dielectric maximum or Curie temperature. PNRs play a dominant role in the formation of unique characteristics of relaxors and are regarded to be caused by spatial and dynamic heterogeneity. However, a detailed microscopic picture of their evolution depending on temperature or electric field is still the subject of controversy. The elastic and dynamical properties of the Pb(B1/3B′2/3)O3-type relaxor-based ferroelectrics and their solid solutions with pure ferroelectrics have recently been studied extensively by the broadband micro-Brillouin scattering spectroscopy (BMBS) to clarify the role of PNRs. This paper reviews the recent progress in the understanding of fast dynamics of PNRs of typical relaxor-based ferroelectrics of (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 and (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 in the gigahertz frequency range achieved by using BMBS.

Elaboration et caractérisations diélectriques de céramiques ferroélectriques et/ou relaxeur de formule MSnO 3-NaNbO 3 (M = Ba, Ca) N° d'ordre 2964 Remerciement A. AYDI 1 Remerciements Ce travail de recherche est le résultat d'une convention en cotutelle entre la Faculté des

Lead-free Zr-modified Bi 0.5 (Na 0.78 K 0.22 ) 0.5 TiO 3 ceramics (BNKTZ-100x, with x = 0-0.05) were synthesized by a conventional ceramic fabrication process and its influence on crystal structure and electromechanical properties was investigated. The temperature-dependent dielectric peaks of the BNKTZ-100x ceramics broadened and ferroelectric polarizations decreased with increasing Zr concentration. The BNKTZ-3 ceramics showed an enhanced unipolar field-induced strain of 0.43%. The dynamic piezoelectric coefficient (d * 33 = S max /E max ) obtained for this composition was 614 pm/V, much higher than that of polycrystalline lead-free and hard Pb(Zr,Ti)O 3 ceramics. These results indicate that an appropriate amount of Zr substitution significantly enhances the field-induced strain level of BNKT ceramics and can be considered as one of promising candidate materials for lead-free electromechanical actuator applications.

The Ba(Zr 0.2 Ti 0.8 )O 3 -x(Ba 0.7 Ca 0.3 )TiO 3 system was synthesized in a wide compositional range in order to study the relationship between its phase diagram and electromechanical properties. Phase transitions were marked using peaks in temperature-dependent permittivity, providing up to three transitions from the rhombohedral phase to an orthorhombic, tetragonal and finally cubic phase, which meet in a region that is termed the phase convergence region in this work. In situ small and large signal electromechanical properties were studied as a function of temperature with specific emphasis on these transitions. A small signal piezoelectric coefficient, d 33 , presents maximized values at the transition from the orthorhombic to the tetragonal phase, while a large signal piezoelectric coefficient, d à 33 , does so at both rhombohedral to orthorhombic and to tetragonal phase transitions. Maximum polarization P max was the only quantity determined that had a clear maximum at the phase convergence region.

A non-volatile memory ferroelectric-gate field-effect transistor (FeFET), fabricated with à dual (top and bottom) channel is demonstrated. This transistor consists entirely of the following thin films: Heavily doped Silicon (Si n++) substrate with thermally grown silicon dioxide (SiO 2 ) (bottom gate electrode); poly[(vinylidenefluoride-co-trifluoroethylene] (P(VDF-TrFE)) (ferroelectric) and gallium indium zinc oxide (GIZO) (semiconductor). The channel conductance of the transistor was controlled by varying the bottom gate bias, while keeping the top gate bias constant. In both cases (positive & negative bottom gate bias), memory device (top & bottom) gates were performed essentially to investigate the chances of enhancing 1) the dipole switching/programming speed to a practical level, and 2) the retention behavior of the memory transistor by controlling the onset voltage.

The annealing temperature for 250 nm PVDF-TrFE (70:30 mol %) spin coated thin films were varied at solvent evaporation (T s = 79 ˚C), Curie's transition (T c = 113 ˚C ) , till melting temperature (T m = 154 ˚C). XRD measurement showed that, there was an improvement in the crystallinity of the annealed films, consistent with the increased in the annealing temperatures. Morphological studies of the annealed PVDF-TrFE thin films as observed with Field Emission Scanning Electron Microscope (FESEM) (100k magnification), showed enhanced development of elongated crystallite structures known as ferroelectric crystal. However, thin film annealed at 160 ˚C (AN160) showed fibrous-like structure with appearance of nanoscale separations, which suggested high possibility of defects. Ferroelectric characterization indicated an improvement in the remnant polarization of annealed PVDF-TrFE thin films with the exception to AN160 in which leakage of current was inevitable due to the presence of cracks on the film surface.

The piezoelectric and the ferroelectric properties of x-mol% Li-doped 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 x = 0, lead-free piezoelectric thin films deposited on Pt (111)/Ti/SiO2/Si substrates via a metal-organic solution deposition method were investigated. Our results show that the Li-substituted film has a remarkable improvement in electrical properties compared with the BNT-BT film. We also found that the substitution was effective in decreasing the coercive field in the thin films. The enhanced electromechanical properties are contributed by both crystal structure evolution and improved microstructure. The optimal ferroelectric properties were obtained in the film with x = 10 providing a remanent polarization (Pr) and a coercive field (Ec) of ∼23.9 µC/cm 2 and ∼124 kV/cm, respectively.

Polycrystalline Ba(Gd1/2Nb1/2)O3 was prepared using a hightemperature solid-state reaction method. X-ray diffraction analysis indicated the formation of a single-phase cubic structure having space group m Pm3 . AC impedance plots as a function of frequency at different temperatures were used to analyse the electrical behaviour of the sample, which indicated the negative temperature coefficient of resistance character. Complex impedance analysis targeted non-Debye type dielectric relaxation. Frequency dependent ac conductivity data obeyed Jonscher's power law. The apparent activation energy was estimated to be 0.17 eV at 1 kHz.

Epitaxial thin films of Bi2FeCrO6 have been synthesized by pulsed laser deposition on SrRuO3 on (100)- and (111)-oriented SrTiO3 substrates. Detailed X-ray diffraction and cross-section transmission electron microscopy analysis revealed a double perovskite crystal structure of the Bi2FeCrO6 epitaxial films very similar to that of BiFeO3 along with a particularly noteworthy Fe3+/Cr3+ cation ordering along the [111] direction. The films contain no detectable magnetic iron oxide impurities and have the correct cationic average stoichiometry throughout their thickness. They however exhibit a slight modulation in the Fe and Cr compositions forming complementary stripe patterns, suggesting minor local excess or depletion of Fe and Cr. The epitaxial BFCO films exhibit good ferroelectric and piezoelectric properties, in addition to magnetic properties at room temperature, as well as an unexpected crystallographic orientation dependence of their room temperature magnetic properties. Our results qualitatively confirm the predictions made using the ab-initio calculations: the double-perovskite structure of Bi2FeCrO6 films exhibit a Fe3+/Cr3+ cation ordering and good multiferroic properties, along with the unpredicted existence of magnetic ordering at room temperature.

This work highlights the low-cost fabrication and characterization of perovskite BaTiO 3 nanoscale particles. X-ray diffraction studies show that an insufficient reaction time at $800°C will not result in the formation of the perovskite BaTiO 3 structure, whereas over-sintering ($900°C) results in BaTiO 3 and by-products of BaTi 2 O 5 . The polyvinyl alcohol polymer-dispersed nano-BaTiO 3 system exhibits a proportionately large remanent polarization ($1 lC cm À2 ) and coercive field (70 kV cm À1 ). The inexpensive synthesis is attractive for large-scale production and device application.

The annealing temperature for 250 nm PVDF-TrFE (70:30 mol %) spin coated thin films were varied at solvent evaporation (T s = 79 ˚C), Curie's transition (T c = 113 ˚C) , till melting temperature (T m = 154 ˚C). XRD measurement showed that, there was an improvement in the crystallinity of the annealed films, consistent with the increased in the annealing temperatures. Morphological studies of the annealed PVDF-TrFE thin films as observed with Field Emission Scanning Electron Microscope (FESEM) (100k magnification), showed enhanced development of elongated crystallite structures known as ferroelectric crystal. However, thin film annealed at 160 ˚C (AN160) showed fibrous-like structure with appearance of nanoscale separations, which suggested high possibility of defects. Ferroelectric characterization indicated an improvement in the remnant polarization of annealed PVDF-TrFE thin films with the exception to AN160 in which leakage of current was inevitable due to the presence of cracks on the film surface.

In this review we describe and discuss recent results on the linear dielectric response of high-permittivity dielectric crystals and ceramics in the wide frequency range 10 2 -10 14 Hz. Our attention is paid to materials which exhibit some interesting low-frequency polar-phonon anomalies in combination with some additional dielectric dispersion below the polar phonon region. The following compounds are discussed: . For these materials the polar phonon spectra are discussed together with their flow-frequency dielectric response and dispersion regions in between, in the 10-300 K or higher temperature range, depending on the existing phase transitions of interest. Some universal features of the disorder and anharmonicities are pointed out: central-mode phenomena near displacive phase transitions and polar nano-clusters which appear at rather high temperatures and remain present down to low temperatures if the material remains structurally disordered. The manifestation of the latter in the dielectric spectra consists in extreme broadening of the relaxation region on cooling which at low temperatures results in constant loss spectra (1/f noise).

This paper gives closed-form equations for the intermodulation and third harmonic signals generated in a nonlinear transmission line with distributed quadratic nonlinearities in the conductor and dielectric. Although the formulation developed is general, it is intended to be used in planar devices combining high-temperature superconductor (HTS) and oxide ferroelectrics. The analysis in this paper shows that the intermodulation and third harmonic signals produced by an HTS tend to cancel those of a ferroelectric, and that full cancellation is theoretically possible. This opens the way for using HTS/ferroelectric multilayers, not (only) for their tunable or phase-shifting properties, but for highly linear spurious-free planar HTS devices.

Elementary Pt/ SrBi 2 Ta 2 O 9 / Pt ferroelectric capacitors have been structurally characterized by x-ray diffraction using highly brilliant synchrotron radiation. A microstructural analysis of the stacked layers was performed from the collection of high-quality one-dimensional and two-dimensional diffraction patterns. During x-ray diffraction experiments, peculiar electrical behaviors under irradiation were evidenced. Indeed, depending upon their initial state ͑poled or nonpoled͒, the capacitors have exhibited drastic changes in their electrical characteristics after or under irradiation, both "fatiguelike" ͑polarization reduction͒ and/or "imprintlike" ͑voltage shift͒ phenomena being observed. Using a sample environment specially designed to measure in situ the evolutions of ferroelectric characteristics, the kinetics of both degradation and restoration of ferroelectric properties of the SrBi 2 Ta 2 O 9 -based capacitors under x-ray radiation have been analyzed. Reduction and recovery of switchable polarization have been explained in terms of interaction between ferroelectric domain configuration and photoinduced charge carriers. Mechanisms of charge trapping proposed in the literature are discussed to explain aging and rejuvenation.

Ferroelectrics materials have been tremendously attractive since the 40 s with the discovery of ferroelectricity in metal oxide perovskite materials and more precisely in barium titanate. Due to their high potential for industrial applications, intensive research has been carried out to better understand their behavior and develop processes to produce them. Trying to face the down scaling demand of high quality particles towards the nanometer range, some conventional methods such as the solid state one reach their limits. The development of other processes are thus required and the synthesis in supercritical fluids can be considered as a promising alternative. This technology exhibits very interesting characteristics such as fast continuous synthesis (few seconds) of high quality nanoparticles (well crystallized nanoparticles with narrow size distribution) with controlled composition (Ba 1Àx Sr x TiO 3 with 0 6 x 6 1) at intermediate synthesis temperatures (<400°C) with the use of non-toxic solvents (water, ethanol). Reaching the nanometer size range, the intrinsic properties of ferroelectric materials change compared to the bulk. Consequently a deep study concerning the crystalline structure, the presence of defects and the surface chemistry of those nanoparticles has to be achieved to control their properties for further use in functional devices.

Enhanced electrocaloric response has been obtained for Pb(Mn 1/3 Nb 2/3 )O 3 -32PbTiO 3 Á(PMN-32PT) single crystal by the application of uniaxial compressive pre-stresses. It was observed that an improvement of the electrocaloric effect (DT elec = 0.62 K) to the tune of 200% can be obtained for an applied compressive of 28 MPa against a conventional unstressed peak electrocaloric effect (DT elec = 0.27 K). Furthermore, the accompanying large strain variations and second order structural transition of the single crystal can be used to obtain significantly large values of elastocaloric effect (DT elas 0.36 K) for an operating temperature of 323 K and applied compressive stress of 2-28 MPa (at 1.5 MV m À1 ). The magnitude of elastocaloric response is even larger than the conventional unstressed DT elec of 0.27 K for the same operating temperature. The results indicate that ferroelectric materials possess significant multicaloric potential and can yield better cooling when employed as elastocaloric materials as opposed to conventional electrocaloric effect. Additionally, the two individual caloric effects can be suitably combined to obtain a further enhanced multicaloric DT of À0.63 K using a novel electro-mechanical thermodynamic cycle for an optimized operating temperature of 323 K and applied compressive stress of 2-14 MPa. The results of this study are expected to largely benefit the field of ferroelectric solid-state refrigeration and open new horizon for future exploration of multicaloric potential in ferroelectric materials.

We present a quantitative analysis of the phonon lineshapes obtained by neutron inelastic scattering methods in the relaxor ferroelectric Pb(Mg 1/3 Nb 2/3 )O3 (PMN). Differences in the shapes and apparent positions of the transverse acoustic (TA) and transverse optic (TO) phonon peaks measured in the and Brillouin zones at 690 K are well described by a simple model that couples the TA and soft TO modes in which the primary parameter is the wave vector and temperature-dependent TO linewidth Γ(q, T ). This mode-coupling picture provides a natural explanation for the uniform displacements of the polar nanoregions, discovered by Hirota et al., as the PNR result from the condensation of a soft TO mode that also contains a large acoustic component.

Ferroelectrics are very interesting materials for nonvolatile data storage due to the fact that they deliver very low power programming operation combined with nonvolatile retention. For 60 years researchers have been inspired by these fascinating possibilities and have tried to build ferroelectric memory devices that can compete with mainstream technologies in their respective time. The progress of the current concepts is limited by the low compatibility of ferroelectrics like PZT with CMOS processing. Therefore, PZT or SBT based 1T1C ferroelectric memories are not scaling below 130 nm and 1T ferroelectric FETs based on the same materials are still struggling with low retention and very thick memory stacks. Hafnium oxide, a standard material in sub 45 nm CMOS, can show ferroelectric hysteresis with promising characteristics. By adding a few percent of silicon and annealing the films in a mechanically confined manner. Boescke et al. demonstrated ferroelectric hysteresis in hafnium o...

We report neutron scattering measurements of the structural correlations associated with the apparent relaxor transition in K$_{1-x}$Li$_x$TaO$_3$ for $x=0.02$ (KLT(0.02)). This compound displays a broad and frequency-dependent peak in the dielectric permittivity, which is the accepted hallmark of all relaxors. However, no evidence of elastic diffuse scattering or any soft mode anomaly is observed in KLT(0.02) [J. Wen et al., Phys. Rev. B 78, 144202 (2008)], a situation that diverges from that in other relaxors such as PbMg$_{1/3}$Nb$_{2/3}$O$_3$. We resolve this dichotomy by showing that the structural correlations associated with the transition in KLT(0.02) are purely dynamic at all temperatures, having a timescale on the order of $\sim$THz. These fluctuations are overdamped, non-propagating, and spatially uncorrelated. Identical measurements made on pure KTaO$_3$ show that they are absent (within experimental error) in the undoped parent material. They exhibit a temperature depen...

The present work reports the elaboration and physical investigation of new compounds of the following composition Ba 1−x Na x (Ti 1−y Sn y) 1−x Nb x O 3 (BTSnNxy). The studied ternary system presents some continuous solid solutions between the next 3 phases: the NaNbO 3 antiferroelectric phase that becomes easily ferroelectric at low rate substitutions, the BaTiO 3 ferroelectric phase and the paraelectric stannate phase BaSnO 3. Two different dielectric behaviors can be observed once some substitutions are made either in A or B sites of an ABO 3 perovskite. These substitutions modify the dielectric properties of the material. The introduction of Sn 4+ and Ti 4+ cations in the B site favors, respectively, a decrease of the transition temperature and an increase in the value of the real dielectric permittivity. The transition temperature should be modulated by varying the rate of cationic substitution. Some relaxor materials can be obtained at a temperature around room temperature.

Solar energy harvesting through pyroelectric effect has been under the scrutiny of researchers since the past few years. However, the low energy density coupled with requirement of rapid temperature fluctuations has hindered any successful commercial ventures in this field. This study is an attempt towards eliminating these drawbacks associated with pyroelectric energy generation using ferroelectric polymers. Langmuir-Blodgett Polyvinylidene difluoride copolymer-Trifluoroethylene-Chlorofluoroethylene P(VDF-TrFE-CFE) thin films were used in conjunction with pyroelectric effect and forced cooling to simultaneously increase energy and power density. In this regard, a two faceted approach of linear pyroelectric harvesting and harvesting through Ericsson cycle have been analyzed and compared. The models for the same have been developed and analyzed using finite-element method. Two separate cases of air cooling and water cooling were investigated. Peak values of power density for water cooling and air cooling processes (direct pyroelectric effect) are found to be 0.437 lW/cm 3 and 0.2 lW/cm 3 , respectively. These values are obtained at optimized value of load resistance and load capacitance (R L = 7 MX and C L = 2 lF for water cooling while R L = 14 MX and C L = 2 lF for air cooling). The maximum values of power density that can be obtained from water and air cooling process are 19.65 mW/cm 3 and 16.35 mW/cm 3 (using Ericsson cycle) at 0.013 and 0.011 Hz frequency, respectively. It was also observed that water cooling is more efficient than air cooling for energy harvesting. This study can lead to growth in the field of solar energy harvesting using pyroelectric effect.

We report neutron inelastic scattering and high-resolution x-ray diffraction measurements on single crystal 0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3 (PMN-0.32PT), a relaxor ferroelectric material that lies within the compositional range of the morphotropic phase boundary (MPB) where the piezoelectric properties of PMN-xPT compounds are close to maximal. Data were obtained between 100 and 600 K under zero and nonzero electric field applied along the cubic [001] direction. The lowest-energy, zone-center, transverse optic phonon is strongly damped and softens slowly at high temperature; however, the square of the soft-mode energy begins to increase linearly with temperature as in a conventional ferroelectric, which we term the soft-mode ``recovery,&#x27;&#x27; upon cooling into the tetragonal phase at TC . Our data show that the soft mode in PMN-0.32PT behaves almost identically to that in pure PMN, exhibiting the same temperature dependence and recovery temperature even though PMN exhibits no ...

We studied the dielectric properties of SrTiO 3 (STO) thin film prepared by pulsed laser deposition in a mixture of 18 O 2 / 16 O 2 gas during deposition. We fabricated an STO capacitor from an YBa 2 Cu 3 O 7 /SrTiO 3 /YBa 2 Cu 3 O 7 multilayer structure by using patterning, ion milling, and chemical mechanical planarization. The temperature dependence of r of STO thin film prepared in a 70% 18 O 2 shows Curie-Weiss behavior down to 2 K without any indication of transition to the ferroelectric state. The frequency dependence of ε r at 2.2 K shows that ε r is almost constant in the region between 0.1 kHz and 1 MHz. This differs from the behavior of ε r of an STO thin film prepared in pure 16 O 2 , which increased as frequency decreased. The result indicates that only small amount of 18 O atoms could be incorporated during deposition, and most of the oxygen atoms were transferred from the target.

Polycrystalline Ba(Gd1/2Nb1/2)O3 was prepared using a hightemperature solid-state reaction method. X-ray diffraction analysis indicated the formation of a single-phase cubic structure having space group m Pm3 . AC impedance plots as a function of frequency at different temperatures were used to analyse the electrical behaviour of the sample, which indicated the negative temperature coefficient of resistance character. Complex impedance analysis targeted non-Debye type dielectric relaxation. Frequency dependent ac conductivity data obeyed Jonscher's power law. The apparent activation energy was estimated to be 0.17 eV at 1 kHz.

The authors present a novel approach for electro-mechanical energy conversion over a wide frequency domain by employing lead-free ferroelectric ceramics. The methodology aims at utilizing Ericsson-like cycle for giant electromechanical energy conversion. Systematic application of electrical and mechanical fields for cyclic polarization switching leads to enhanced energy generation densities. The reported energy density, achieved by using 0.94(Bi 0.5 Na 0.5 )TiO 3 -0.05(BaTiO 3 )-0.01(K 0.5 Na 0.5 )NbO 3 lead-free ferroelectric ceramic, is three orders of magnitude larger than that reported for leading lead-based ferroelectric materials. Estimated energy density was found to be 940kJ.m −3 which is significantly higher than conventional piezoelectric harvesters.

Polycrystalline Ba(Gd1/2Nb1/2)O3 was prepared using a hightemperature solid-state reaction method. X-ray diffraction analysis indicated the formation of a single-phase cubic structure having space group m Pm3 . AC impedance plots as a function of frequency at different temperatures were used to analyse the electrical behaviour of the sample, which indicated the negative temperature coefficient of resistance character. Complex impedance analysis targeted non-Debye type dielectric relaxation. Frequency dependent ac conductivity data obeyed Jonscher's power law. The apparent activation energy was estimated to be 0.17 eV at 1 kHz.

Electronic structure calculations of cubic SrTiO 3 and SrHfO 3 are presented. The full-potential linear augmented-plane-wave method is used and exchange-correlation effects are treated by the local-density approximation. The tendency to ferroelectricity of both compounds is explored and compared by displacing the transition metal atom ͑Ti or Hf͒ towards one of the oxygens ͑001 direction͒. The calculations show that ferroelectricity is favored in SrTiO 3 with respect to SrHfO 3 and that this fact may be correlated with the degree of hybridization between transition metal d-O p bands as has been found for other related systems. Also a detailed discussion of the calculated electric field gradients is presented.

This research was conducted to study the effect of ZnO nano-particulate modification on properties of Pb(Zr 0.52 Ti 0.48 )O 3 (PZT)-(Bi 3.25 La 0.75 )Ti 3 O 12 (BLT) ceramics prepared by a mixed-oxide solid-state sintering method. ZnO nano-particulate was added into PZT-BLT ceramics to obtain PZT-BLT/xZnO (x = 0, 0.1, 0.5 and 1.0 wt%). The PZT-BLT/xZnO ceramics were investigated in terms of phase, microstructure, physical, electrical, and mechanical properties. Tetragonality of PZT-BLT crystal structure tended to increase with increasing ZnO content. ZnO addition obviously increased the density of PZT-BLT ceramics while the grain size slightly decreased. Intergranular fracture mode was observed for pure PZT-BLT ceramic while the samples contained ZnO nano-particles showed a mixed-mode inter-/trans-granular fracture. Addition of ZnO also affected hardness and fracture toughness values. Addition of ZnO nano-particulate into PZT-BLT ceramics was found to improve room temperature dielectric constant but did not have a significant effect on ferroelectric properties. These observed results were expected to be caused by the behaviors similar to a donor-doped system. #

We have used neutron scattering techniques that probe time scales from 10−12 to 10−9 s to characterize the diffuse scattering and low-energy lattice dynamics in single crystals of the relaxor PbMg1/3Nb2/3O3 (PMN) from 10 to 900 K. Our study extends far below Tc=213 K, where long-range ferroelectric correlations have been reported under field-cooled conditions, and well above the nominal Burns temperature Td≈620 K, where optical measurements suggest the development of short-range polar correlations known as “polar nanoregions” (PNR). We observed two distinct types of diffuse scattering. The first is weak, relatively temperature independent, persists to at least 900 K, and forms bow-tie-shaped patterns in reciprocal space centered on (h00) Bragg peaks. We associate this primarily with chemical short-range order. The second is strong, temperature dependent, and forms butterfly-shaped patterns centered on (h00) Bragg peaks. This diffuse scattering has been attributed to the PNR because it responds to an electric field and vanishes near Td≈620 K when measured with thermal neutrons. Surprisingly, it vanishes at 420 K when measured with cold neutrons, which provide approximately four times superior energy resolution. That this onset temperature depends so strongly on the instrumental energy resolution indicates that the diffuse scattering has a quasielastic character and demands a reassessment of the Burns temperature Td. Neutron backscattering measurements made with 300 times better energy resolution confirm the onset temperature of 420±20 K. The energy width of the diffuse scattering is resolution limited, indicating that the PNR are static on time scales of at least 2 ns between 420 and 10 K. Transverse acoustic (TA) phonon lifetimes, which are known to decrease dramatically for wave vectors q≈0.2 Å−1 and Tc<T<Td, are temperature independent up to 900 K for q close to the zone center. This motivates a physical picture in which sufficiently long-wavelength TA phonons average over the PNR; only those TA phonons having wavelengths comparable to the size of the PNR are affected. Finally, the PMN lattice constant changes by less than 0.001 Å below 300 K but expands rapidly at a rate of 2.5×10−5 K−1 at high temperature. These disparate regimes of low and high thermal expansions bracket the revised value of Td, which suggests the anomalous thermal expansion results from the condensation of static PNR.

We have performed elastic diffuse neutron-scattering studies on the relaxor Pb(Mg1/3Nb2/3)O3. The measured intensity distribution near a (100) Bragg peak in the (hk0) scattering plane assumes the shape of a butterfly with extended intensity in the (110) and (11¯0) directions. The temperature dependence of the diffuse scattering shows that both the size of the polar nanoregions and the integrated diffuse intensity increase with cooling even for temperatures below the Curie temperature TC∼213K.

ABSTRAK Oksida Aurivillius dengan rumus, CuBi 5 Ti 5 O 18 dan AgBi 5 Ti 5 O 18 telah disintesis dengan metode reaksi kimia padat. Oksida Aurivillius yang diperoleh berupa padatan polikristalin. Oksida hasil sintesis berwarna abu kekuningan untuk AgBi 5 Ti 5 O 18 dan coklat untuk CuBi 5 Ti 5 O 18. Penentuan tipe struktur kristal dilakukan menggunakan data difraksi sinar-X serbuk dan penelusuran struktur dengan program Phasanx dengan data base PDF. Hasil analisis difraktogram menunjukkan bahwa senyawa-senyawa yang diperoleh berstruktur Aurivillius fasa tunggal mempunyai group ruang A2 1 am sistim kristal ortorombik dengan parameter sel satuan masing

Fluorine is used in liquid crystal materials in order to give them particular properties as compared to their hydrocarbon homologues. This leads to use of the new compounds as materials mainly in display devices such as Twisted Nematic Liquid Crystals Display (TNLCD) or for the development of Surface Stabilized Ferroelectric smectic C* display (SSFLCDs). In this paper, we describe recent studies and research effort concerning the liquid crystalline behavior of compounds incorporating a highly¯uorinated part with more than one¯uoromethylene units. We examine some of their mesophase properties and the impact of molecular shape on the resulting liquid crystal behavior.

X-ray and neutron scattering studies of the lead-based family of perovskite relaxors Pb(Zn 1/3 Nb 2/3)O 3-xPbTiO 3 (PZN-xPT) and Pb(Mg 1/3 Nb 2/3)O 3-xPbTiO 3 (PMN-xPT) have documented a highly unusual situation in which the near-surface region of a single crystal can exhibit a structure that is different from that of the bulk when cooled to low temperatures. The near-surface region, or ''skin'' can also display critical behavior that is absent in the crystal interior, as well as a significantly different lattice spacing. By varying the incident photon energy, and thus the effective penetration depth, X-ray measurements indicate a skin thickness of order 10-50 mm for PZN-xPT samples with 0 x 8%. Neutron residual stress measurements on a large PMN single crystal reveal a uniform lattice spacing within the bulk, but an increased strain near the surface. The presence of this skin effect has led to incorrect phase diagrams for both the PZN-xPT and PMN-xPT systems and erroneous characterizations of the nature of the relaxor state.

The frequency dependent electrical parameters, such as impedance, electric modulus, dielectric constant and AC conductivity for ferroelectric Ba0.8Sr0.2TiO3 thin film have been investigated within the range of 1 Hz and 106 Hz at room temperature. Z* plane shows two regions corresponding to the bulk mechanism and the distribution of the grain boundaries-electrodes process. M&quot; versus frequency plot reveals a relaxation peak, which is not observed in the ε″ plot and it has been found that this peak is a non-Debye-type. The frequency dependent conductivity plot shows three regions of conduction processes, i. e., a low-frequency region due to DC conduction, a mid-frequency region due to translational hopping motions and a high-frequency region due to localized hopping and/or reorientational motion.

Nanocrystalline lead zirconate titanate (PZT) and lead lanthanum zirconate titanate (PLZT) have been synthesized in powder form by a single-step auto-ignition of metal–polymer gel precursor. The nanocrystalline powders were characterized using analytical transmission electron microscopy (TEM) equipped with an energy-dispersive x-ray spectrometer (EDXS) for composition analysis. For both PZT and PLZT, nanoparticles of sizes as low as 1–5 nm along with larger nanoparticles of sizes up to 30 nm are observed in the TEM. The selected-area diffraction (SAD) patterns from the nanoparticles revealed a face-centered cubic (fcc) crystal structure for both PZT and PLZT with a lattice parameter of ∼0.51 nm. The formation of PZT and PLZT nanoparticles of sizes below 5 nm with metastable fcc crystal structure has been observed for the first time. It is concluded that, as the crystal size decreases, the system assumes crystal structures of higher symmetry initially through small changes in lattice...

Ceramics with composition belonging to the SrSnO 3-NaNbO 3 system were sintered in the temperature range 1100-1350 • C. The symmetry, dielectric properties and Raman spectroscopy were investigated. Xray diffraction results demonstrate that a region with the cubic or tetragonal phases lies in the composition range x < 0.89 and x ≥ 0.89, respectively. The thermal behavior of the dielectric permittivity suggests the existence of two phases: cubic-paraelectric and tetragonal-ferroelectric or ferroelectric relaxor. The Raman spectra was recorded at room temperature and their evolution related to the chemical composition.

In the present study, the authors have employed, for the first time, AFM for observing the surfaces of ferroelastic materials. Studies of ferroelectricrferroelastic domains are important for understanding the devices based on acousto-optic and opto-electronic properties and the aging behavior of the ferroelectricrferroelastic crystals. This paper reports the first such study of domains on the ferroelastic lead vanadate crystal surface. Both stripes and needle-shaped domains are observed. The typical width of the tip of needle domains is ; 100 A. Sharp and round tips of needles have been detected very clearly with developed surface features. q 1998 Elsevier Science B.V.

Broad-frequency range dielectric data of strontium barium niobate with 61% of Sr, from kHz to THz range, has been studied using various experimental techniques (FTIR, time-domain THz spectroscopy, HF coaxial technique and standard LF dielectric spectroscopy) in a wide interval of temperatures (20-600 K). Strong dielectric anisotropy was seen by all the experimental methods. Relaxor properties were detected in the ε * c response, where an intense relaxation slows down from the microwave range (T > T m ) and broadens to low frequencies on cooling. The slowing down stops below MHz near 200 K. On further cooling it disappears gradually from the spectra leaving a constant loss background. The high-frequency wing of this relaxation is seen also in the THz range at high temperatures. IR modes show standard behaviour with decreasing temperature and no anomalies in phonon frequencies were observed. This brings evidence for the order-disorder type of the ferroelectric phase transition. Dielectric data perpendicular to the polar axis show anomalous features at low temperatures, but there is no sufficient evidence for another phase transition suggested by other authors below 100 K.

New ferroelectric or relaxor ceramics with composition Na 1−x Li x Nb 1−x Sb x O 3 (0.05 ≤ x ≤ 0.30) were elaborated and sintered in the temperature range 1100-1200 • C. The effect of cationic substitution of the sodium with the lithium in the A site and the niobium with the antimony in the B site in the NaNbO 3 perovskite lattice on physical properties were investigated. X-ray diffraction at room temperature and dielectric permittivity in the temperature range from 200 to 500 K with frequencies from 0.1 to 200 kHz characterisations were used. X-ray diffraction analysis demonstrates that all samples have a single phase with quadratic perovskite structure. Dielectric measurements show that the material have a classical ferroelectric behaviour for 0 < x ≤ 0.15 and a relaxor one for 0.20 ≤ x ≤ 0.30. The polarisation state was checked by pyroelectric and piezoelectric measurements. For x = 0.20, the piezoelectric coefficient d 31 is of 15.3 pC/N.

Preparation, dielectric, piezoelectric, hysteresis, impedance spectroscopy and AC conductivity studies in the Pb0.8K0.4Nb2O6 ferroelectric ceramic have been presented. The Pb1−xK2xNb2O6 (PKN) characterized for ferroelectric and impedance spectroscopy studies from room temperature to 600 °C. The sample shows a single phase with orthorhombic structure from X-ray diffraction studies. The Cole–Cole plots and electric modulus plots at different temperatures are drawn. The results obtained from the impedance spectroscopy are analyzed, to understand the conductivity behavior of PKN. The piezoelectric constant, d33, has been found to be 75 × 10−12 C/N.