Defect structure‐electrical property relationship in Mn‐doped calcium strontium titanate dielectric ceramics

Ca_0.6Sr_0.4TiO₃ (CST) ceramics with different amounts of Mn dopant (0‐2.0 mol%) were prepared by solid‐state reaction method. The electric field and temperature stability of energy storage performance was found to be greatly enhanced with moderate doped level of 0.5 mol%. The dielectric loss‐frequency spectra revealed the existence and evolution of defect dipoles at elevated temperature, which was confirmed directly by electron paramagnetic resonance (EPR) spectra. The response of defect dipoles was characterized by thermally stimulated depolarization current (TSDC), where the activation energy and the concentration evolution of defect dipoles were calculated, with the highest values observed for 0.5% doped samples. The dissociation of defect dipoles and the movement of free were analyzed by high‐temperature impedance spectra analysis, with the activation energy of 1.04‐1.60 eV, and 0.5% doped samples also demonstrated the highest E_a. The relationship between microscopic defect structure and macroscopic electrical behavior was established in this work.     

Effects of defect dipoles on tunable dielectric response in relaxor ferroelectric ceramics

Tunable dielectric materials have drawn much attention due to their wide applications including capacitors and microwave tunable devices. Ferroelectrics materials have special spontaneous polarization which can be reversibly switched by an external electric field. Therefore, tunable dielectric constant can be easily achieved in ferroelectrics. However, the study of nonlinear dielectric response induced by defect dipoles is rarely concerned. Here, we report the effects of defect dipoles on tunable dielectric response under alternative current (AC) and direct current (DC) electric field in defect dipoles introduced Pb(Lu_1/2Nb_1/2)O₃–PbTiO₃ ceramics. A modified Rayleigh model is proposed to successfully characterize dielectric nonlinearity and reveals the interaction between domain walls and defect dipoles. The defect dipoles had more sensitive effect on dielectric response under AC field than that of defect dipoles-free samples. The drop of intrinsic dielectric contribution under AC field results from the detriment effect of defect dipoles. The irreversible contribution is altered by the movements of defect dipoles under AC field, subsequently inducing the nonlinearity of dielectric response. Samples with defect dipoles have larger tunable scope of dielectric properties than that of defect dipoles-free samples. The present work discovers the potential of application of defect dipoles-tuned dielectric response ferroelectrics in devices which requires both high AC and DC biases, and help to better understand the complex dielectric response of ferroelectrics.     

Defect dipole evolution and its impact on the ferroelectric properties of Fe-doped KTN single crystals

The ferroelectric and piezoelectric properties of doped potassium tantalum niobate crystals with different Fe doping amounts and the adjustability of the properties are investigated. The hysteresis loops and current density curves show that the defect dipoles have an obvious effect on domain reorientation, and the effect decreases with increasing doping amount. The ferroelectric and piezoelectric properties can be adjusted via the defect dipoles, and the adjustability is reduced with increasing doping amount. A change of the doping amount leads to defect dipole structure evolution in the crystals, in which the defect dipoles transform from a polar structure to a nonpolar structure, which is the reason for the transition of the domain reorientation determined by the defect dipoles. This result has proved that introducing defects is an effective way to improve and regulate perovskite properties, and the doping amount is one of the important factors controlling the defect dipoles.     

Dislocation Structures in Sapphire Deformed by Basal Slip

Dislocation structures in sapphire deformed by basal slip at 1200° to 1500°C were studied by transmission electron microscopy. Long dislocation dipoles of edge character are formed by interactions of dislocations on parallel basal planes ("edge-trapping"); screw dislocations annihilate by cross-slip. The accumulation of dislocation dipoles leads to work-hardening, but the dipoles also break up into smaller loops by climb, causing recovery. Eventually a steady state of zero work-hardening is reached, where the rate of accumulation of dipoles by edge-trapping is equal to their rate of annihilation by climb. From these observations, it is suggested that dislocation climb plays an important role in the deformation process for basal slip in the range 1200° to 1500°C.     

Dielectric relaxation induced internal electric field and its effect on magnetoelectric state in Co4Nb2O9

Pyrocurrent and dielectric properties of magnetoelectric antiferromagnet Co₄Nb₂O₉ have been investigated. The sample shows 2 thermally activated dielectric relaxations in the temperature range far above Néel temperature with the low‐ and high‐temperature ones being a dipolar and Maxwell‐Wagner relaxations, respectively. Two types of dipoles: relaxing dipoles and magnetic‐field‐induced dipoles were found in the sample. An internal electric field is formed due to the ordering of relaxing dipoles. Three current peaks were observed. The 2 higher temperature current peaks correspond to the dielectric relaxations. The lowest temperature current peak contains a positive tip and negative dip. The tip and dip are related to the depolarization of ferroelectricity induced by external and internal fields, respectively.     

Determination of Pipe Diffusion Coefficients in Undoped and Magnesia-Doped Sapphire (α-Al2O3): A Study Based on Annihilation of Dislocation Dipoles

The breakup of dislocation dipoles in plastically deformed samples of undoped and 30-ppm-MgO-doped sapphire (α-Al₂O₃) was monitored using conventional TEM techniques. Dislocation dipoles break up into prismatic dislocation loops in a sequential process during annealing; i.e., dislocation loops are pinched off at the end of a dislocation dipole. This pinch-off process is primarily controlled by pipe diffusion, and pipe diffusion coefficients at temperatures between 1300° and 1500°C were estimated by monitoring the kinetics of the dipole breakup process. We determined D _P^U= 8.1(_–4.3^+9.1) × 10^–3 exp [–(4.5 ± 1.3 eV )/ kT )] m²/s for the undoped material. The pipe diffusion kinetics for the MgO-doped crystal was determined at 1250° and 1300°C and was about 6 times higher than for undoped sapphire. Finally, climb dissociation of the dislocations constituting the perfect dipoles in sapphire is common; annihilation of one set of partials can result in the formation of faulted dipoles, which can pinch off to form faulted dislocation loops. D _P^U for faulted dipoles in the undoped material was determined at 1300° and 1350°C, and was about 4–10 times higher than for perfect dipoles.     

Multi-field tuning of dielectric relaxation in epitaxial multiferroic hexaferrite thin film around room temperature: Property and mechanisms

Understanding the dielectric relaxation properties of multiferroic hexaferrite thin films is crucial for device applications. This work investigates the dielectric relaxation characteristics (DRC) of multiferroic hexaferrite BaFe_10.2Sc_1.8O₁₉ (BFSO) thin film under multi-fields. The alternative driving voltage and biasing voltage V_b were found to have significant effects on the DRC of BFSO/electrode interface dipoles, but negligible effects on the intrinsic dipoles in BFSO film. The DRC mechanism of a BFSO film capacitor under a magnetic field is opposite to that of V_b; is dominated by intrinsic dipoles in BFSO, and is thermally activated. The temperature-dependent magnetodielectric spectra confirm that multiferroic dipoles in BFSO significantly impact the DRC of the capacitor, which is different from the DRC of nonmagnetic ceramic capacitors. The above findings can clarify the DRC mechanisms and integration of multiferroic hexaferrite thin films in magnetoelectric devices.     

Influence of polarization,reorientation, and coupling of dipole on electrocaloric effect in ferroelectrics

Electrocaloric effects due to entropy change and dipole coupling upon electric field in second-order phase transition (tetragonal-cubic) ferroelectrics are investigated by a three-dimensional Devonshire's theory and statistic method. In diabatic condition, increase in vibration entropy to heat the ferroelectric is due to decreases in polarization entropy and configuration entropy of dipole reorientation in the specific directions. Coupling effect originated from the reorientation of dipoles accompany with electric hysteresis loop happens in the nearest neighbor dipoles parallel to electric field direction. Numerical simulations exhibit that polarization effect causes electrocaloric peak at the Curie's temperature independent of electric field, reorientation effect of dipole causes a shift of electrocaloric peak to high temperature with electric field, and coupling effect between dipoles gives rise to increase in electrocaloric effect with decreasing temperature. A method to predetermine the excellent electrocaloric effect of ferroelectrics from dielectric and/or polarization experimental results is proposed.     

The secondary relaxation process of poly(vinyl chloride) and its derivatives

The temperature dependence of the shear modulus G′ and of the damping tan δ of poly-(vinyl chloride), poly(vinylidene chloride), copolymers of vinyl chloride–vinylidene chloride, PVC chlorinated in solution and suspension, and chlorinated polyethylene was measured. Secondary relaxation process of PVC and its derivatives are being explained as vibration of methylene groups polarized by neighboring CCl dipoles. This process, being suppressed by lowering the concentration of the methylene groups in the PVC chain (e.g., by chlorination), remains, however, unaffected by the growth of crystalline content. The achieved results show that in the α-transition region there occurs, in accordance with Andrews' theory, a loosening of the bonds between the CCl dipoles, whereas in the β-transition region a loosening of the weaker bonds among the dipoles of the polarized methylene.     

Dynamic mechanical and dielectric relaxation characteristics of poly(trimethylene terephthalate)

The dynamic mechanical and dielectric relaxation properties of a commercial poly(trimethylene terephthalate) [PTT] have been investigated for both quenched and isothermally melt-crystallized specimen films. The relaxation characteristics of PTT were consistent with those of other low-crystallinity semiflexible polymers, e.g. PET and PEEK. While the sub-glass relaxation was largely unperturbed by the presence of the crystalline phase, both calorimetric and broadband dielectric measurements across the glass transition indicated the existence of a sizeable rigid amorphous phase (RAP) fraction in melt-crystallized PTT owing to the constraining influence of the crystal surfaces over the crystal-amorphous interphase region. A strong increase in measured dielectric relaxation intensity (Δ?) with temperature above T_g indicated the progressive mobilization of the RAP material, as well as an overall loss of correlation amongst the responding dipoles.     

Discovery and evolution of double P‐E loops in a tetragonal Fe‐doped KTa0.57Nb0.43O3 single crystal

Double polarization‐electric field (P‐E) loops were observed in Fe‐doped KTa_0.57Nb_0.43O₃ (Fe‐KTN) crystals because of the restraining effect of the defect dipoles on domain reorientation. In Fe‐KTN crystals, the positively charged O^2? vacancies and negatively charged dopant Fe³⁺ ions form defect dipoles, providing a restoring force for domain reorientation. Moreover, built‐in macro‐polarization was observed depending on the orientation of the defect dipole polarization. The response of the defect dipoles to an external electric field and the evolution of the double P‐E loops were investigated. The restraining effect of the defect dipoles on domain reorientation was found to affect normal piezoelectric activities. The domains could maintain the state close to the polarization direction, resulting in an extremely high d₃₃ value (287 pC/N).     

Effect of Blending with Polysulfone on Thermally Stimulated Discharge Behavior of Polyvinylidenefluoride Films

Thermally stimulated depolarization current (TSDC) have been undertaken on solution grown foil samples of polyvinylidenefluoride (PVDF)-polysulfone (PSF) blends as a function of the polarizing temperature, applied field, and polysulfone weight percentage in the blend. The TSDC thermograms of pure PVDF and PSF shows two peaks whereas the blend composition of the two polymers shows a single peak at around 170–190°C. The magnitude of the TSDC peak current increases and the peak current position shifted toward the lower temperature side as the polysulfone weight percentage in the blends was increased. The peak temperature of blend samples is higher than the dipolar peak (β peak) of PVDF samples and does not vary with change in polarizing field. This indicates that this peak may be due to dipoles. At the same time, the peak shifts towards higher temperatures with increase in polarizing temperature, which shows the behavior of space charge peak. This contradiction may be explained on the basis of induced dipoles. It seems that the charge originating from the bulk of the samples gets trapped in the deeper traps during polarization, and thus form induced dipoles. Afterward these induced dipoles get aligned in the polarizing field. It can be explained on the basis that either the dipolar peak gets covered by the space charge peak, or its contribution to the total polarization is very small.     

Differential capacitance studies of the specific adsorption of thiosulfate on silver

The differential capacitance of a polycrystalline Ag electrode was measured in a NaClO4 electrolyte containing Na2S2O3 at concentrations ranging from 0.1 to 20mm and at electrode potentials ranging from –0.9 to –0.3V vs SCE. The differential capacitance measurements were analysed to obtain the surface coverage of specifically adsorbed thiosulfate (S2O32–) as a function of both electrode potential and bulk concentration. The various forms for the adsorption isotherm at an electrochemical interface which are commonly employed are reviewed and discussed. The adsorption behaviour is best explained by the formation of image dipoles by the specifically adsorbed ions, whose energetic interactions are then dominated by repulsion of like dipoles. The adsorption data is quantitatively fit to an adsorption isotherm for interacting dipoles, yielding an effective dipole moment of 0.72D for the system S2O32–/Ag.     

Pb(Zn,Nb)(Sn,Nb)(Zr,Ti)O3材料的介电性能研究

通过分析PZSN系材料的介电温度与介电频率曲线 ,发现PZSN系材料没有明确的相变温度 ,相变属弥散型相变。 12 5K与 4M处的介电频率峰对应O -Ti-O与O -Zr -O的偶极子的空间取向的响应行为 ,在顺电相T >Tcav时这种偶极子是不存在的 ,说明它们的行为与相变有关     

Size Effects in the Transition Temperature of Small Ising Systems

Monte Carlo simulations of the phase transition in small Ising dipolar systems: nanocubes with L 3 dipoles (4 ≤ L ≤100), nanoplates with L 2 dipoles (4 ≤ L ≤1100), and nanochains with L dipoles (4 ≤ L ≤1000) using free boundary conditions did allow us the determination of the transition temperature T c ( L ) as a function of size ( L ). Simple effective field expressions for T c ( L , L c ) in terms of the large size transition temperature T c ( ∞, L c ) for d = 3, d = 2 and T ¯( L ) for d = 1 are shown to fit quite well T c for nanocubes (previously investigated) and nanoplates (present work), and are approximately fitted in a certain range for nanochains (in which case T c for an infinitely long chain is known to evolve slowly towards zero).     

Temperature dependence of the internal bias in TGS-alanine crystals near Tc

The temperature, driving field amplitude and frequency dependence of hysteresis loops of triglycine sulfate doped with L-alanine has been examined in the neighborhood of the Curie temperature, T_c: The magnitude of the internal bias associated with L-alanine content shows a remarkable temperature dependence near T_c, decreasing by more than two orders of magnitude within ±1°C of T_c. A semiquantitative interpretation of this behavior in terms of the interaction between orient able (glycine) dipoles and fixed (L-alanine) dipoles is given.     

Dielectric Relaxation in Zr‐Doped SrTiO3 Ceramics Sintered in N2 with Giant Permittivity and Low Dielectric Loss

SrTiZr_xO₃ (x = 0, 0.002, 0.006, 0.01, and 0.014) ceramics with a weak temperature‐dependent giant permittivity (>10⁴) and a very low dielectric loss (<0.01) were fabricated using the conventional solid‐state reaction method by sintering them in N₂ at 1500°C. With increasing Zr content, the permittivity decreased from approximately 48 000 to 18 000 and the dielectric loss decreased from approximately 0.005 to 0.003. According to the XRD, XPS, and ac conductivity analysis, the dielectric properties of pure SrTiO₃ ceramics sintered in N₂ were due to the existence of the giant defect dipoles generated by the fully ionized oxygen vacancies and Ti³⁺ ions, while the dielectric properties of SrTiZr_xO₃ (x > 0) ceramics were also influenced by the defect dipoles (). The giant permittivity and low dielectric loss phenomenon could be explained by giant defect dipoles related to oxygen vacancies.     

Potentials of zero charge,interaction of metals with water and adsorption of organic substances—III. The role of the water dipoles in the structure of the dense part of the electric double layer

Two types of solvent particles resident on the electrode surface have been considered: (1) associates of water molecules freely oriented along the electric field and (2) chemisorbed water dipoles oriented with the oxygen atom towards the metal surface. On the basis of this model, a semi-quantitative interpretation has been given to the dependence of the differential capacity of the dense layer on the electrode charge. It has been shown that a change in this dependence, when passing from mercury to gallium, can be described assuming the energy of interaction of chemisorbed water dipoles with the metal surface to increase.     

On the mechanism of conductivity enhancement in poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film through solvent treatment

The conductivity of a poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film is enhanced by more than 100-folds on adding some organic compounds into PEDOT:PSS aqueous solutions or by treating the PEDOT:PSS film with organic solvents, such as ethylene glycol (EG), 2-nitroethanol, methyl sulfoxide or 1-methyl-2-pyrrolidinone. The mechanism for this conductivity enhancement was studied through various chemical and physical characterizations. The PEDOT:PSS film which is soluble in water becomes insoluble after treatment with EG. This strongly suggests an increased interchain interaction among the PEDOT chains. Raman spectroscopy indicates that this increased interchain interaction results from conformational changes of the PEDOT chains, which change from a coil to linear or expanded-coil structure. The increased interchain interaction and conformation changes are further confirmed by the temperature dependence of conductivity and the electron spin resonance (ESR). It is found that EG treatment lowers the energy barrier for charge hopping among the PEDOT chains, lowers the polaron concentration in the PEDOT:PSS film by ∼50%, and increases the electrochemical activity of the PEDOT:PSS film in NaCl aqueous solution by ∼100%. Atomic force microscopy (AFM) and contact angle measurements show that the surface morphology of the PEDOT:PSS film changes as well after the EG treatment. Conductivity enhancement was also observed when other organic compounds were used, but it was strongly dependent on the chemical structure of the organic compounds, and observed only with organic compound with two or more polar groups. These experimental results support our proposal that the conductivity enhancement is due to the conformational change of the PEDOT chains and the driving force is the interaction between the dipoles of the organic compound and dipoles or charges on the PEDOT chains.     

Dielectric relaxations in polyoxymethylene and in related nanocomposites: Identification and molecular dynamics

Broadband dielectric spectroscopy (BDS) is employed for the study of the dielectric response of Polyoxymethylene/boehmite alumina (POM/alumina) and Polyoxymethylene/Layered Silicates (POM/LS) semi-crystalline nanocomposites, together with the response of pure POM. The compilation of the dielectric responses of all systems reveals the existence of five dielectric relaxation mechanisms assigned, in terms of decreasing temperature at constant frequency, as IP (interfacial polarization), α-, β-, γ- and δ-relaxations. IP, α- and γ-relaxations are detected in all studied systems and they are well documented in the literature. δ-relaxation, been the fastest mechanism, is present only in the POM/LS system and is associated with defect dipoles in the crystalline phase of POM. Finally, β-relaxation is present only in the POM/alumina nanocomposite and its dynamics obey Vogel–Fulcher–Tamann temperature dependence. This work presents a complete mapping of the dielectric relaxation mechanisms of POM and signifies the connection of β-mode with the glass to rubber transition of POM, confirming its cooperative character.