Distinct Dielectric Relaxations Research Articles

Effect of B-site Zr and Hf substitution on ferroelectric polar order for tetragonal tungsten bronze ceramic

ABSTRACT Lead free ferroelectric ceramic Ba4Sm2Hf4Nb6O30(BSHN) with tungsten bronze structure was synthesized and characterized. The effect of B-site cation electron configuration (Hf and Zr) on origin of ferroelectricity and polarization reversal was also studied in detail. The X-ray diffraction (XRD) pattern was indexed with tetragonal tungsten bronze in P4bm space group for BSHN. Obvious dielectric anomaly was observed in the temperature dependent permittivity curve, and quite large thermal hysteresis was obtained from the differential scanning calorimetry (DSC) result. While at lower temperature (<T C), there are two distinct dielectric relaxations for BSHN, respectively related to the activation of frozen polar region and activation of the fully free reversal for the polarization. Compared with Ba4Sm2Zr4Nb6O30(BSZN), Hf substitution in B site makes it harder to activate the frozen polar nanoregion but easier to realize free polarization reversal. This could be further confirmed by the measured polarization-electric field (P-E) curve. Meanwhile, the Raman modes intensity showed gradual change rather than abrupt one for BSHN when the temperature increased through the Curie point, which was quite different from the Zr based compounds. The difference in BO6 octahedral tilting, B-site cation’s electron configuration and B-O bond character are the main cause of these distinct dielectric and ferroelectric property.

Coexistence of dielectric relaxation and magnetic relaxation in compressively strained BiFeO3/Ba0.7Sr0.3TiO3 superlattices

Superlattices (SLs) consisting of multiferroic BiFeO3 (BFO) and dielectric Ba0.7Sr0.3TiO3 were epitaxially grown on a (001)-oriented Nb:SrTiO3 substrate using pulsed laser deposition. An improved ferroelectricity with a high-temperature polarization of ∼63.7 μC/cm2 at 470 K was observed. The SL exhibited both dielectric and magnetic relaxation properties. Two distinct dielectric relaxations were found: a carrier hopping process between Fe2+ and Fe3+ from 273 to 410 K and the long-range migration of oxygen vacancies from 430 to 573 K. Spin-glass behavior with a freezing temperature of ∼86.6 K was also observed. This work provides a promising path forward to tailor the multiferroic properties of BFO-based structures for high-temperature applications.

Dielectric relaxation and relevant mechanism in giant dielectric constant Sm2/3Cu3Ti4O12 ceramics

Sm2/3Cu3Ti4O12 ceramics with giant dielectric constant were successfully prepared by the traditional solid-state sintering process. The dielectric characteristics and relevant mechanism were systematically investigated. The dielectric constants of Sm2/3Cu3Ti4O12 ceramics can reach to 104 at 298 K and 1 kHz, and also exhibited two distinct thermal-activated dielectric relaxations in different temperature ranges. The dielectric relaxation at low temperatures was regarded as the effect of the polyvalence structures (Cu2+/Cu3+ and Ti3+/Ti4+) in grains due to the oxygen compensation during the sintering process, while the dielectric relaxation at high temperatures was induced by the grain boundary effects. The giant dielectric response in Sm2/3Cu3Ti4O12 ceramics can be associated with the heterogeneous structure and combined effect of the grain and grain boundary.

Effect of grafting density on conformation of poly(acrylic acid) in solution by dielectric spectroscopy.

The effect of grafting density of poly(ethylene oxide) and dodecyl groups on the conformation of poly(acrylic acid) in solution was clarified by dielectric relaxation spectroscopy over a frequency range from 40 Hz to 110 MHz. Two distinct dielectric relaxations were found after the elimination of electrode polarization, and valuable information about the conformations and interfacial electrokinetic properties of molecules was obtained by analyzing the dielectric spectra based on a refined double-layer polarization model. The critical aggregation concentration was determined by the concentration dependency of dielectric parameters. The results based on zeta potential suggested that the ionization performance and behavior of counterion condensation were strongly influenced by the grafting density of poly(ethylene oxide) and dodecyl groups. The concentration dependency of correlation length, ratio of zeta potential, ratio of linear density of counterions, and the Debye length showed that the chain length and degree of intermolecular aggregation were also strongly influenced by the grafting density. We revealed the role of grafting density with respect to electrostatic interaction in determining the chain conformation of polyelectrolytes in solution.

Real-time monitor on the release of salicylic acid from chitosan gel beads by means of dielectric spectroscopy

The release processes of salicylic acid (SA) from the chitosan gel beads (CGB) with different crosslinking densities were monitored in real time by means of dielectric spectroscopy. Distinct dielectric relaxations attributed to interfacial polarization were observed, which exhibited obvious dependences on the crosslinking density and the release time. In line with Hanai’s equation, the properties of CGB and release media were quantitatively determined from the dielectric profiles. Based on these properties and dielectric behaviors, the release profiles were analyzed. It was found that only the dispersion of CGB with the lowest crosslinking density exhibited release behavior, while other dispersions showed an obvious adsorption process following a burst of drug diffusion. The total loading and release amount of SA were determined and compared, and the influence of crosslinking degree on the drug loading and release was discussed. In addition, the release behavior was confirmed to be diffusionally controlled, and the diffusion coefficient of SA was determined.

FERROELECTRIC AND DIELECTRIC PROPERTIES OF LEAD ZIRCONATE TITANATE MULTILAYERS

Ferroelectric and dielectric properties of the PbZr0.38Ti0.62O3(PZT) multilayer with a unique structure were explored.Compared with the uniform PZT thin films,the PZT multilayer with alternating dense-PZT and porous-PZT layers exhibits an enhancement both in ferroelectric and dielectric performances.The PZT multilayer has an average remanent polarization of 42.3C/cm2 and an average coercive field of 43kV/cm under an applied voltage of 100V.The large value of remanent polarization is attributed to the effective relaxation of the tensile stress in film due to large film thickness and porous structure.The apparently relative dielectric constant of the PZT multilayer is more than 2000 at room temperature and low frequency limit.More interestingly,two distinct dielectric relaxations have been observed in the PZT multilayer in the investigated frequency range.The low-frequency loss peak originates from space charge polarization,while the high-frequency dielectric response following an Arrhenius-law is expected to be related to the dipolar defect complexes associated with oxygen vacancies VO¨.

Dielectric analysis of chitosan gel beads suspensions: Influence of low crosslinking agent concentration on the dielectric behavior

Dielectric measurements were carried out for the suspensions of chitosan gel beads (CGB) crosslinked with glutaraldehyde (GA), ranging in crosslinking time from 1 to 180 min at six fixed low GA concentrations over a frequency range from 40 to 110 MHz. The distinct dielectric relaxations observed in the frequency range of 10(4)-10(5) Hz were explained by the effects of the interfacial polarization. By fitting the experimental data with Cole-Cole equation the dielectric parameters of the suspensions were obtained, and the phase parameters were calculated using Hanai's method. The influence of crosslinking on the dielectric spectra of CGB was investigated by viewing the crosslinking time dependencies of conductivity increment (Deltakappa), relaxation frequency (f(0)), permittivity of CGB (epsilon(i)), conductivity of CGB (kappa(i)) and conductivity of continuous media (kappa(a)) at six fixed GA concentrations. Some information were gained, such as, thinner electric double layer, particle with rougher surface and more compact gel backbone with increasing crosslinking time. The basic information obtained can provide valuable references for the preparation of CGB and the application to more extensive fields such as controlled-release technology of medicament.

Dielectric Behaviour of Ice Microcrystals: A Study Versus Temperature

AbstractDispersions of ice microcrystals were obtained from the breakdown of supercooling of water-in-oil type emulsions whose disperse phase was either resin-exchanged water or aqueous solutions of NH4Cl. Their complex permittivity ε⋆ = ε´–jε˝ was studied versus temperature T, up to the melting point of ice microcrystals, by means of an automatically balancing admittance bridge (General Radio 1680 A) working at 400 Hz and 1 kHz, The plots ε´(T), ε˝(T) and ε˝(ε´) reveal that these systems exhibit two distinct dielectric relaxations located on either side of a temperature Tm which was found to be equal to about — 20°C in the case of water and lower than — 20°C in the case of aqueous solutions of NH4Cl. The relaxation located in the lower temperature range arises from the Debye dipolar absorption of ice while the other one could be related to structural changes occurring within the lattice of ice as T approaches its melting point. These results are consistent with those obtained by investigating versus frequency the dielectric behaviour of ice monocrystals at discrete sub-zero temperatures close to their melting point.

Dielectric Behaviour of Ice Microcrystals: A Study Versus Temperature

AbstractDispersions of ice microcrystals were obtained from the breakdown of supercooling of water-in-oil type emulsions whose disperse phase was either resin-exchanged water or aqueous solutions of NH4Cl. Their complex permittivity ε⋆ = ε´–jε˝ was studied versus temperatureT,up to the melting point of ice microcrystals, by means of an automatically balancing admittance bridge (General Radio 1680 A) working at 400 Hz and 1 kHz, The plots ε´(T), ε˝(T) and ε˝(ε´) reveal that these systems exhibit two distinct dielectric relaxations located on either side of a temperatureTmwhich was found to be equal to about — 20°C in the case of water and lower than — 20°C in the case of aqueous solutions of NH4Cl. The relaxation located in the lower temperature range arises from the Debye dipolar absorption of ice while the other one could be related to structural changes occurring within the lattice of ice asTapproaches its melting point. These results are consistent with those obtained by investigating versus frequency the dielectric behaviour of ice monocrystals at discrete sub-zero temperatures close to their melting point.

Dielectric Behaviour of Ice Microcrystals: A Study Versus Temperature

Abstract Dispersions of ice microcrystals were obtained from the breakdown of super-cooling of water-in-oil type emulsions whose disperse phase was either resin-exchanged water or aqueous solutions of NH4C1. Their complex permittivity ϵ* = ϵ′ - ϵ″ was studied versus their temperature T, up to the melting point of the ice microcrystals, by means of an automatically balancing admittance bridge (General Radio 1680A) working at 400 Hz and 1 kHz. The plots ϵ′(T), ϵ″(T), and ϵ″(ϵ′) reveal that these systems exhibit two distinct dielectric relaxations located on both sides of a temperature T m which was found to be equal to about —20°C in the case of water and lower than —20°C in the case of aqueous solutions of NH4C1. The relaxation located in the lower temperature range arises from the Debye dipolar absorption of ice while the other one could be related to structural changes occurring within the lattice of ice as T approaches its melting point. These results are consistent with those obtained by investigating versus frequency the dielectric behaviour of ice microcrystals, at discrete sub-zero temperatures close to their melting point. This paper has been accepted for publication in full in a forthcoming issue of the Journal of Glaciology.

Dielectric Behaviour of Ice Microcrystals: A Study Versus Temperature

AbstractDispersions of ice microcrystals were obtained from the breakdown of super-cooling of water-in-oil type emulsions whose disperse phase was either resin-exchanged water or aqueous solutions of NH4C1. Their complex permittivity ϵ* = ϵ′ - ϵ″ was studied versus their temperature T, up to the melting point of the ice microcrystals, by means of an automatically balancing admittance bridge (General Radio 1680A) working at 400 Hz and 1 kHz. The plots ϵ′(T), ϵ″(T), and ϵ″(ϵ′) reveal that these systems exhibit two distinct dielectric relaxations located on both sides of a temperature Tm which was found to be equal to about —20°C in the case of water and lower than —20°C in the case of aqueous solutions of NH4C1. The relaxation located in the lower temperature range arises from the Debye dipolar absorption of ice while the other one could be related to structural changes occurring within the lattice of ice as T approaches its melting point. These results are consistent with those obtained by investigating versus frequency the dielectric behaviour of ice microcrystals, at discrete sub-zero temperatures close to their melting point.This paper has been accepted for publication in full in a forthcoming issue of the Journal of Glaciology.