Dielectric and ferroelectric materials

High voltage cable terminations are widely used in power system networks. A proper design of cable termination is essential in reducing the electric field distribution around the end of high voltage cable. However, if there are defects exist at cable termination structure, the electric field can be enhanced significantly and can be the source of electrical discharges. Therefore, it is important to understand the effect of defects on the electric field distribution at cable terminations. In this work, a 132 kV XLPE outdoor cable termination has been modelled using finite element analysis (FEA) method. The model has been used to simulate the electric field distribution in the cable termination in the presence of defects. Defects that have been considered are void defect in porcelain, stress cone and fluid, sharp pin on the porcelain surface and delamination defect between the insulator and the stress cone. The effect of different void location, material dielectric constant and porcelain radius on the electric field magnitude at cable termination have also been investigated. From the results obtained in this work, a better understanding of the electric field distribution at the cable termination with defects can be attained. © 2012 IEEE.

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The binary niobate ceramics, with the formula M2+Nb2O6 where M2+=Ca, Mg, or a transition metal (TM), have the orthorhombic columbite structure. The best-known members of this group are zinc niobate (ZnNb2O6) and magnesium niobate (MgNb2O6), but Ca, Co, Ni, Mn, Cu, Cd, and Fe 2+ cations can also be included in the columbite structure. The TM columbite niobates have been found to sinter at temperatures of 1100°–1200°C, much lower than the complex perovskites, and this can be lowered even more when Cu2+ is used. The best columbite niobates have Q×f values similar to those of BaZn0.33Nb0.67O3, and all have ɛr between 17 and 25 and negative τf values of <−80 ppm/°C. There is a growing interest in the columbites as microwave dielectric ceramics, due to their lower processing temperatures, less complicated processing due to the simple chemistry of the binary compounds, and the lower cost of niobium compared with tantalum, and with incorporation of Cu2+ they are approaching low-temperature cofired ceramics (LTCC) temperatures. They have also been investigated combined with other dielectric ceramics (to compensate for the negative τf values), and with additives to lower sintering for LTCC. Furthermore, MgNb2O6 is in wide use as a precursor to synthesize single phase PMN (Pb(Mg1/3Nb2/3)O3) in the “columbite” process, and NiNb2O6 is being increasingly investigated as a catalyst for splitting water and organic compounds. CoNb2O6 and other columbites have interesting magnetic properties, and CaNb2O6 and CdNb2O6 have useful optical properties. This review covers the various means of synthesis of these ceramics, and the effects of processing upon structural, physical, electronic, and optical properties. This review will concentrate on the dielectric properties and applications, as this is the greatest area of interest, but will also cover other properties and applications of these ceramics. All available reported microwave dielectric data for columbites is compiled, compared, and assessed.

In this paper, we discuss the effect of the lattice model in dielectric or ferroelectric materials. The lattice model is used when we study the film configuration which includes the surface effec effective medium approach reflectivity of attenuated total reflection (ATR). Employing this formulation, we calculate numerically ATR reflection spectra by taking parameters appropriate for BaTiO lead to the existence of the disturbance in ATR spectra. The frequency frequency if the number of lattice is increased. The equivalent to bulk thickness. Keywords-Lattice model The Attenuated Total Reflection (ATR) is a non functional material. This method enables sample material to be analysed directly without doing specific preparation. This technique is able to examine both aqueous and solid samples. is successfully used in proof the emergence of magnon multiferroic system to get the magno reflection phenomena, therefo ensures total reflection in the bottom of prism if t elementary excitation of the material excitation of sample decrease. In ferroelectrics samples where the elementary excitation is phonon resulted from l electromagnetic waves will couple to the phonons around the phonon frequency of the sample. Hence, the ATR reflectance decreases near this frequency illustrating the generation of the phonon polaritons. represents surface modes while the shallow decrease illustrates bulk modes. reflectance for ferroelectric sample, homogeneous parameter. This is an open access article distributed under the terms of the Creative Commons Attribution License, Which Permits unrestricted use, distribution, and reproduction in any medium, provid and source are credited In this paper, we discuss the effect of the lattice model in dielectric or ferroelectric materials. The lattice model is used when we study the film configuration which includes the surface effec effective medium approach, the electric susceptibility is derived. Using this susceptibility, we derived the reflectivity of attenuated total reflection (ATR). Employing this formulation, we calculate numerically ATR by taking parameters appropriate for BaTiO lead to the existence of the disturbance in ATR spectra. The frequency frequency if the number of lattice is increased. The disturbance will disappear when the number of lattice is equivalent to bulk thickness.

The application of combinatorial methods to materials science offers the opportunity to accelerate the discovery of more efficient dielectric ceramics. High throughput methods have the potential to investigate the effects of a wide range of dopants on the dielectric properties, and to optimise existing systems, encouraging the short innovation cycles that the communications technology industry requires. The London University Search Instrument (LUSI) is a fully automated, high-throughput combinatorial robot that has the potential capability to produce 1000's of sintered bulk ceramic samples with varying composition in 1 day, as combinatorial libraries on alumna substrates. The LUSI robot was demonstrated to be able to automatically print and sinter libraries of bulk ceramic Ba1−xSrxTiO3 (BST), for x = 0–1 in steps of 0.1. The samples were prepared from inks consisting of suspensions of BaTiO3 and SrTiO3 nanopowders, stabilised with 1.2 wt% dispersant. The samples were printed as arrays of 22 2mm diameter dots, two of each composition, on alumina substrates. These were then sintered at 1350 and 1400 • C/1 h by LUSI. EDXA and XRD confirmed the compositional gradient throughout the libraries, and SEM showed the samples to be well sintered, with a large 20 m grain size for pure BaTiO3 decreasing rapidly for increasing x values.

First layer Aurivillius Bismuth Molybdate Tungstate ceramic [Bi 2 Mo 1−x W x O 6 (BMoW); x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.10] compositions are prepared using deep penetrating microwave sintering in air. All samples show known perovskite phase formation just after 5 h calcinations at 575 °C. X-ray diffraction and transmission electron microscopy based energy dispersive spectroscopy are used to confirm the phase-purity and gross elemental concentration change besides particle size. Nearly double-values are obtained for investigated BMoW materials compared to earlier reported values. Silver percolation through electrodes in bismuth oxide deficient surfaces of BMoW ceramic powders induces radio wave absorption in the frequency range 2 to 4 MHz. Characteristic third phase transition (→) of Bi 2 MoO 6 material dissolves gradually on increasing tungsten concentration. The introduction of tungsten in BMo matrix increases the dipolar strength of MoO 6 octahedrons bending against infrared absorption as evidenced from FTIR analysis. Additionally appearing FTIR peaks provide a strong indication of CO and CO 2 contamination on exposed powder surfaces useful for photocatalytic applications.

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...

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 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.

We report lattice-dynamical measurements, made using neutron inelastic-scattering methods, of the relaxor perovskite PbMg1/3Nb2/3O3 (PMN) at momentum transfers near the edge of the Brillouin zone. Unusual “columns” of phonon scattering that are localized in momentum, but extended in energy, are seen at both high-symmetry points along the zone edge: Q⃗ R={12,12,12} and Q⃗ M={12,12,0}. These columns soften at ∼400 K which is similar to the onset temperature of the zone-center diffuse scattering, indicating a competition between ferroelectric and antiferroelectric distortions. We propose a model for the atomic displacements associated with these phonon modes that is based on a combination of structure factors and group theoretical analysis. This analysis suggests that the scattering is not from tilt modes (rotational modes of oxygen octahedra), but from zone-boundary optic modes that are associated with the displacement of Pb2+ and O2− ions. Whereas similar columns of scattering have been reported in metallic and (less commonly) molecular systems, they are unusual in insulating materials, particularly in ferroelectrics; therefore, the physical origin of this inelastic feature in PMN is unknown. We speculate that the underlying disorder contributes to this unique anomaly.

In the present study, we have prepared the [Ba(Nd 0.075 Ti 0.85 Nb 0.075)O 3 ] 0.30-[(Na 0.5 Bi 0.5)TiO 3 ] 0.70 ceramic through solid-state double sintering route. New equations which were proposed by us earlier were used to describe and model the electromechanical, AC and DC resistivity data. The activation energy for resonance and anti-resonance at 300 K is 30.28 and 30.11 meV; whereas the value is 38.32 and 38.91 meV at 448 K. The higher activation energy for AC conduction when compared to DC conduction is attributed to the fast vibration of charged polar and conducting species in response to the applied frequency, which requires more temperature. ARTICLE HISTORY

Dielectric ceramics in the Li2ZnTi3O8 system were synthesized using TiO2 nanoparticle reagent by the reaction-sintering process. The special effects of the TiO2 nanoparticle reagent on the densification, phase distribution, microstructure, and dielectric properties were characterized using powder x-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). A single phase of Li2ZnTi3O8 ceramic was confirmed by the XRD pattern at all temperatures except 1075°C. The reaction between the starting materials was accelerated using TiO2 nanoparticles, with pure Li2ZnTi3O8 phase being created even at low sintering temperature of 900°C, along with increasing green specimen density at the compaction stage. The presence of TiO2 phase in the Li2ZnTi3O8 ceramic improved the  τf  value and shifted it to near zero at 1075°C, and the ceramic exhibited excellent microwave dielectric properties of  εr  = 23.5,  Q×f  = 71,000 GHz, and  τf  = −3.5 ppm/°C.

Strontium hafnium oxide (SrHfO3) has great potential as a high-k gate dielectric material, for use in memories, capacitors, CMOS and MOSFETs. We report for the first time the dielectric properties (relative permittivity and capacitance) of SrHfO3 nanoparticles (NPs), as opposed to thin films or sintered bulk ceramics. These monodisperse, ultra-small, perovskite-type SrHfO3 nanocrystals were synthesised through a non-aqueous sol–gel process under solvothermal conditions (at only 220 °C) using benzyl alcohol as a solvent, and with no other capping agents or surfactants. Advanced X-ray diffraction methods (whole powder pattern modelling, WPPM), CS-corrected high-resolution scanning transmission electron microscopy (HRSTEM), dielectric spectroscopy, and optical (UV-vis, Raman) and photoluminescent spectroscopy were used to fully characterise the NPs. These SrHfO3 NPs are the smallest reported and highly monodisperse, with a mean diameter of 2.5 nm, a mode of 2.0 nm and a small size distribution. The formation mechanism of the NPs was determined using NMR and GC-MS analysis of the species involved. Our SrHfO3 nanoparticles had a dielectric constant of 17, which is on par with literature data for bulk and thin film samples, and they also had a relatively large capacitance of 9.5 nF cm−2. As such, they would be suitable for applications as gate dielectrics for capacitors and in metal-oxide semiconductor field-effect transistor (MOSFET) technology.

Poly(vinylidene fluoride) (PVDF)‐based composites containing up to 30 vol % of lead zirconate titanate (PZT) particles were prepared by: (a) different techniques, melt blending and solvent casting; and (b) different molding procedures, a single‐step and a two‐step hot‐pressing method. The obtained samples were characterized in order to study how the processing affects their final properties. Results indicate that the different molding processes have a strong effect on polymorphism and molecular relaxations of PVDF as well as on dielectric response of the composite materials, that results enhanced by the two‐step molding. The preparation technique influences the filler dispersion and, consequently, the elastic modulus of the composites, but without remarkably impacting on other properties. This suggests the possibility of preparing performing composites by a solvent‐free and easily scalable technique (i.e., melt blending) and obtaining suitable dielectric characteristics, very important for application of such kind of materials, just by tuning the molding conditions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48871.

We revisit the phase diagram of the relaxor ferroelectric PMN-xPT using neutron powder diffraction to test suggestions that residual oxygen vacancies and/or strain affect the ground state crystal structure. Powdered samples of PMN-xPT were prepared with nominal compositions of x=0.10, 0.20, 0.30, and 0.40 and divided into two identical sets, one of which was annealed in air to relieve grinding-induced strain and to promote an ideal oxygen stoichiometry. For a given composition and temperature the same structural phase is observed for each specimen. However, the distortions in all of the annealed samples are smaller than those in the as-prepared samples. Further, the diffraction patterns for x=0.10, 0.20, and 0.30 are best refined using the monoclinic Cm space group. By comparing our neutron diffraction results to those obtained on single crystals having similar compositions, we conclude that the relaxor skin effect in PMN-xPT vanishes on the Ti-rich side of the morphotropic phase boundary.

Neutron diffraction data obtained on single crystals of PbZr1−xTixO3 with x=0.325 and x=0.460, which lie on the pseudorhombohedral side of the morphotropic phase boundary, suggest a coexistence of rhombohedral (R3m/R3c) and monoclinic (Cm) domains and that monoclinic order is enhanced by Ti substitution. A monoclinic phase with a doubled unit cell (Cc) is ruled out as the ground state.

We present high-energy x-ray (67 keV) and neutron-scattering measurements on a single crystal of K1−xLixTaO3 for which the Li content (x=0.02) is less than xc=0.022, the critical value below which no structural phase transitions have been reported in zero field. While the crystal lattice does remain cubic down to T=10 K under both zero-field and field-cooled (E≤4 kV/cm) conditions, the Bragg peak intensity changes significantly at TC=63 K. A strong and frequency-dependent dielectric permittivity is observed at ambient pressure, a defining characteristic of relaxors. However an extensive search for static polar nanoregions, which is also widely associated with relaxor materials, detected no evidence of elastic neutron diffuse scattering between 300 and 10 K. Neutron inelastic scattering methods were used to characterize the transverse acoustic and optic phonons (TA and TO modes) near the (200) and (002) Bragg peaks. The zone-center TO mode softens monotonically with cooling but never reaches zero energy in either zero field or in external electric fields of up to 4 kV/cm. These results are consistent with the behavior expected for a dipolar glass in which the local polar moments are frozen and exhibit no long-range order at low temperatures.

We have used neutron diffraction to characterize the diffuse scattering in five single crystals of the relaxor ferroelectric (1−x)Pb(Mg1∕3Nb2∕3)O3−xPbTiO3 (PMN-xPT) with x=0, 10, 20, 30, and 40%. The addition of ferroelectric PbTiO3 modifies the well-known “butterfly” and “ellipsoidal” diffuse scattering patterns observed in pure PMN (x=0), which are believed to be associated with the presence of randomly oriented polar nanoregions. In particular, the anisotropy of the diffuse scattering diminishes as the PT content increases. The spatial correlation length ξ along the [11¯0] direction derived from the width of the diffuse scattering at room temperature increases from 12.6Å for PMN to 350Å for PMN-20%PT. In addition, the diffuse scattering intensity at q=0 grows and reaches a maximum value around the morphotropic phase boundary (MPB), which suggests that it is proportional to the dielectric susceptibility. Beyond x=30%, a concentration very close to the MPB, no diffuse scattering is observed below TC, and well-defined critical behavior appears near TC. By contrast, the diffuse scattering for x≤20% persists down to low temperatures, where the system retains an average cubic structure (TC=0). Finally, the anisotropic soft transverse optic (TO) modes observed in PMN are found to be isotropic for PMN-30%PT, which strongly suggests a connection between the anisotropic diffuse scattering and the TO modes.

We report high q-resolution neutron scattering data on PMN−xPT single crystals with x=20% and 27%. No rhombohedral distortion occurs in the 20PT sample for temperatures as low as 50 K. On the other hand, the 27PT sample transforms into a rhombohedral phase below TC∼375K. Our data provide conclusive evidence that a phase with an average cubic lattice is present in the bulk of this relaxor system at low PT concentration, in which the ferroelectric polarization and lattice distortion are decoupled. The rhombohedral distortion is limited to the outermost tens of microns of the crystal.