Poling of Lead Zirconate Titanate Ceramics and Flexible Piezoelectric Composites by the Corona Discharge Technique

In the conventional poling method, piezoelectric ceramics and composites are poled by applying a large dc voltage. Poling of composites having a polymer matrix with 0–3 connectivity is especially difficult because the electric field within the high-dielectricconstant grains is far smaller than in the low-dielectric-constant polymer matrix. Therefore, very large electric fields are required to pole these types of composites. However, large electric fields often cause dielectric breakdown of the samples. In this study for improved poling, the corona discharge technique was used to pole piezoelectric ceramics, fired PZT composites, and 0.5PbTiO₃· 0.5BiFeO₃ 0–3 polymer composites. An experimental setup for corona poling is described. The dielectric and piezoelectric properties of materials poled by the corona discharge technique were comparable to those obtained with the conventional poling method.     

Chemical structure and mechanical properties of soda lime silica glass surfaces treated by thermal poling in inert and reactive ambient gases

This study employed thermal poling at 200°C as a means to modify the surface mechanical properties of soda lime silica (SLS) glass. SLS float glass panels were allowed to react with molecules constituting ambient air (H₂O, O₂, N₂) while sodium ions were depleted from the surface region through diffusion into the bulk under an anodic potential. A sample poled in inert gas (Ar) was used for comparison. Systematic analyses of the chemical composition, thickness, silicate network, trapped molecular species, and hydrous species in the sodium‐depleted layers revealed correlations between subsurface structural changes and mechanical properties such as hardness, elastic modulus, and fracture toughness. A silica‐like structure was created in the inert gas environment through restructuring of Si–O–Si bonds at 200°C in the Na‐depleted zone; this occurred far below T_g. This silica‐like surface also showed enhancement of hardness comparable to that of pure silica glass. The anodic thermal poling condition was found so reactive that O₂ and N₂ species can be incorporated into the glass, which also alters the glass structure and mechanical properties. In the case of the anodic surfaces prepared in a humid environment, the glass showed an improved resistance against crack formation, which implies that abundant hydrous species incorporated during thermal poling could be beneficial to improve the toughness.     

Enhancement of mechanical properties and chemical durability of Soda-lime silicate glasses treated by DC gas discharges

We report for the first time a study on non-contact thermal poling of soda lime silicate glasses using DC gas discharge. In this work, the formation of a glow discharge is evidenced during the thermal poling treatment (longer than 30 minutes). The hardness and the chemical durability of glasses poled under different conditions (contact or non-contact) and atmospheres (nitrogen or air) are measured and compared to that of un-poled reference glass. The results reveal enhanced mechanical and chemical properties for samples poled under nitrogen as compare to air poled or soda lime silicate glass samples. A structural and chemical analysis of surface of the glass using IR-reflectance measurement and ToF-SIMS is also presented. The formation of a “silica-like” layer on the surface of nitrogen poled glasses is observed, which is likely associated with the enhancement of surface properties. On the other hand, the introduction of protons beneath the surface of glasses poled under air leads to the formation of a hydrated alkaline earth silica layer. Based on the observations a mechanism behind the sustainability of the plasma under DC conditions is proposed.     

Plasmonic molecules via glass annealing in hydrogen

Growth of self-assembled metal nanoislands on the surface of silver ion-exchanged glasses via their thermal processing in hydrogen followed by out-diffusion of neutral silver is studied. The combination of thermal poling of the ion-exchanged glass with structured electrode and silver out-diffusion was used for simple formation of separated groups of several metal nanoislands presenting plasmonic molecules. The kinetics of nanoisland formation and temporal evolution of their size distribution on the surface of poled and unpoled glass are modeled.

PACS

78.67.Sc (nanoaggregates; nanocomposites); 81.16.Dn (self-assembly); 68.35.bj (surface structure of glasses); 64.60.Qb (Nucleation); 81.16.Nd (micro- and nanolithography)     

IR and XPS Studies on the Surface Structure of Poled ZnO–TeO2 Glasses with Second-Order Nonlinearity

The effect of thermal/electrical poling on the surface structure of 30ZnO·70TeO₂ glass has been investigated by means of IR reflectance and X-ray photoelectron spectroscopy (XPS). All the poled glasses exhibit a common characteristic that the second-order nonlinearity is induced preferentially in an anode-side surface region. The reflectance from the anode-side glass surface at around 635 cm^{− 1} assignable to the vibrational mode of the Te–O_ax bond, where ax stands for the axial position of the TeO₄ trigonal bipyramid, is smaller in comparison with both as-annealed and cathode-side surfaces. The XPS analysis of the anode-side surface shows a depletion of Zn²⁺ ions and penetration of Na⁺ ions from the borosilicate glass which was placed between the sample and the anode during poling. These results suggest that the poling brings about both the breaking of the tellurite glass network and compositional changes at the anode-side surface below which the second-order nonlinearity is preferentially induced.     

Dielectric response and polarization mechanism of alkali silicate glasses in gigahertz to terahertz frequency range

Oxide glasses are dielectric materials with potential applications in high-frequency communications; hence, their dielectric properties in the gigahertz to terahertz frequency range should be investigated. In this study, the dielectric properties of silica glass and five single alkali silicate glasses were measured at 0.5–10 THz using terahertz time-domain spectroscopy and far-infrared spectroscopic ellipsometry. At 0.5–10 THz, the silica glass exhibited low dielectric dispersion with a low dielectric constant and loss. By contrast, the alkali silicate glasses exhibited high dielectric dispersion, and the dielectric constant and loss were higher than those of the silica glass. The shape of the dielectric dispersion profile depended on the alkali-metal ions; it was broader for lighter ions such as Li ions and sharper for heavier ions such as Cs ions. The peak dielectric loss shifted toward a lower frequency as the weight of the alkali-metal ions in the alkali-silicate glass increased. To understand the dielectric dispersion, the complex permittivity was calculated using molecular dynamics simulations. The theoretical results qualitatively agreed with the experimental data. Ion dynamics analysis revealed that alkali-metal ions vibrate and migrate under an applied electric field, which affects the dielectric constant and loss of alkali-silicate glasses at gigahertz to terahertz frequencies. To fabricate filter devices at low temperatures, alkali metals should be added to silicate glass; therefore, a minimum amount of light alkali metals should be used to minimize the dielectric loss of the glass materials while maintaining productivity.     

聚偏氟乙烯的宽频介电谱特征研究

采用熔融法制备了聚偏氟乙烯（PVDF）样品,通过X射线衍射仪、傅里叶变换红外光谱仪和宽频介电谱分析仪对PVDF样品的结构及介电性能进行了测试分析。结果表明,熔融法获得的PVDF主要含α相;在40～100℃范围内出现由玻璃化转变引起的α-PVDF的松弛现象, 在-100～-50 ℃范围内出现的δ-PVDF松弛,是由非晶区分子运动产生的极化现象。     

Influences of crystallization temperature on the structure,dielectric, and energy storage characteristics of KBaSrNb5O15-based glass–ceramics

Glass–ceramics capacitors have great application potential in pulsed power systems, due to ultrafast discharge speed and high dielectric breakdown strength (BDS). Here, lead-free niobate glass–ceramic dielectric materials were synthesized, and the effects of heat treatment temperature on the dielectric, ferroelectric, and energy storage properties of glass–ceramics were investigated comprehensively. The results exhibit that the dielectric permittivity first increases and then decreases as the crystallinity increases; however, the dielectric BDS diminishes. At the optimum crystallization temperature of 740°C, the maximum value of discharge energy density is 2.2 J/cm³ at 600 kV/cm, which is about 7.6 times that of mother glass. Furthermore, an ultrahigh power density of about 380.9 MW/cm³ and ultrafast discharge speed of about 11.2 ns were achieved simultaneously. Meanwhile, great thermal stability of charge–discharge property was verified in this glass–ceramics. According to P–E loops and dielectric test result, a high dielectric constant (∼207) and low dielectric loss (<0.005) as well as high energy storage efficiency of about 94.9% were achieved for G740 sample. The previous results make the obtained glass–ceramic as potential candidates in dielectric capacitors.     

Poling of soft piezoceramic PZT

The properties of piezoelectric ceramic materials are strongly dependent on the degree of polarization as set by the poling process. In the present work a soft piezoceramic PZT material was polarized at different poling conditions. The hysteresis loop, the polarization current and pyroelectric current measurements were used to evaluate the polarization state of the material. The hysteresis loop was monitored using a home-made computer controlled Sawyer–Tower circuit. The polarization current was recorded during the poling process at different applied electric fields, poling time and temperature. The pyroelectric coefficient and the polarization were calculated from the pyroelectric current. The polarization calculated from these data was in excellent agreement with the polarization as calculated from the poling current. The relative permittivity and loss factor were measured as a function of temperature after different poling conditions. The effects of the various poling conditions on the dielectric and ferroelectric properties of the soft PZT are discussed. It is shown that, contrary to common practice, poling at a field slightly larger than the coercive field is adequate to reach full polarization at room temperature.     

Insulating characteristics of zinc niobium borate glass‐ceramics

Zinc borate glasses with different concentrations of Nb₂O₅ were prepared and later were heat treated for prolonged times. Prepared samples were characterized by XRD, SEM, DSC, IR and optical transmission spectroscopy techniques. Later, dielectric properties viz., dielectric constant, loss tangent, electric modulii, electrical impedance and a.c. conductivity over wide ranges of frequency and temperature, were investigated as a function of Nb₂O₅ concentration. Finally, the dielectric breakdown strength was measured in air medium at ambient temperature. The results of characterization techniques viz., XRD, SEM and DSC indicated that multiple crystal grains (with sizes varying from 0.1 to 1 μm) are dispersed in the residual glass phase. The concentration of crystal grains found to increase with increase in Nb₂O₅ content. The XRD studies have further revealed that the bulk samples are composed of columbite ZnNb₂O₆ crystal phases. Using generalized gradient approximation (GGA) quantitative information on these crystal phases viz., the lattice parameters, optical band gap and band structure were evaluated. The analysis of results of IR spectral studies have indicated that there is an increasing degree of polymerization of glass network with increase in Nb₂O₅ content due to the increased connectivity between various structural groups in the glass network. The optical absorption spectra indicated an increase in optical transmittance of the bulk samples with increase in Nb₂O₅ content. The dielectric parameters are observed to decrease, whereas the dielectric breakdown strength is observed to increase to a large extent due to the crystallization of the glass with the Nb₂O₅. The increase is attributed to the formation of ZnNb₂O₆ crystalline phases that contain intertwined ZnO₆ and NbO₆ structural units. As a whole, zinc borate glasses exhibited a significant increase in the electrical insulating strength due to the crystallization with Nb₂O₅ as the crystallizing agent. Further, the value of dielectric constant is also found to be the optimal with no dispersion with frequency up to 450 K. Overall, the studied glass‐ceramics meet the necessary physical conditions to be used as insulating layers in the display panels and hence may be considered for such applications.     

Kinetics of the glass transition of styrene-butadiene-rubber: Dielectric spectroscopy and fast differential scanning calorimetry

The glass transition is relevant for performance definition in rubber products. For extrapolation to high-frequency behavior, time–temperature superposition is usually assumed, although most complex rubber compounds might be outside of its area of validity. Fast differential scanning calorimetry (FDSC) with cooling rates up to 1500 K/s and broadband dielectric spectroscopy (BDS) with frequencies up to 20 MHz are applied here to directly access both kinetics and dynamics of glass formation in a wide frequency range. For the first-time, the relation between the thermal vitrification and the dielectric relaxation is studied on vulcanized styrene-butadiene rubber, showing that both cooling rate and frequency dependence of its glass transition can be described by one single Vogel-Fulcher-Tammann-Hesse equation. The results indicate the validity of the Frenkel-Kobeko-Reiner equation. Another focus is the sample preparation of vulcanized elastomers for FDSC and BDS as well as the temperature calibration below 0°C.     

Effect of electric poling on structural,magnetic and ferroelectric properties of 0.8PbFe0.5Nb0.5O3-0.2BiFeO3 multiferroic solid solution

The effect of electric poling on structure, magnetic and ferroelectric properties of 0.8PbFe_0.5Nb_0.5O₃-0.2BiFeO₃ (0.8PFN-0.2BFO) multiferroic was studied through XRD, Raman, magnetic and ferroelectric measurements. Single step solid state reaction method was adopted to synthesize single phase 0.8PFN-0.2BFO multiferroic at lower calcination and sintering temperature. Room temperature (RT) XRD pattern before and after poling confirmed the monoclinic structure with Cm space group. Rietveld refined XRD for poled and unpoled sample shows the influence of electric poling on Fe-O1, Fe-O2, Nb-O and Bi-O modes. There is a small variation in the lattice parameters after electric poling. The structural properties were also studied in detail for the poled and unpoled 0.8PFN-0.2BFO using Raman spectroscopy. Raman measurements were carried out over a wide range of temperature (250–550 K) for both poled and unpoled samples. At RT unpoled 0.8PFN-0.2BFO multiferroic exhibit 8 active modes at 211, 263, 440, 484, 571, 706, 785 and 1120 cm^-1 in the frequency range 100–1200 cm^-1. The Raman peaks exhibits significant changes in intensity as well as shape of the spectra at the characteristic temperature T_C (470 K) and T_N (310 K). Poled Raman spectra show major changes in the Fe/Nb-O modes intensities around T_N and are due to dynamic nature of spin phonon coupling. Changes observed in the temperature dependent magnetic measurements i.e. ZFC/FC and M − H loop evidence the existence of converse magneto-electric coupling (CME) and this is due to the poling effects on Fe-O, Nb-O active modes. Due to rotation of the oxygen octahedral the electric field induced strain will originate in the system. P-E loops after poling show an increase in remnant polarisation and coercive field due to an improvement in domain ordering. The potential tunability of magnetisation with electric poling is an ideal tool for realisation of application in practical devices.     

Comparison of electric field-dependent property in BaTiO3-based piezoceramics between single and coexisting phases

The evolution of electrical properties with an electric field (E) was compared between single-phase BT ceramic and phase-coexistence BT-based (BTS–0.15BCT) ceramic. The dielectric, ferroelectric, piezoelectric, and strain properties are all found to be electric field-dependent, especially for BTS–0.15BCT ceramic with small domains and easy polarization rotation induced by phase coexistence. High ferroelectric and strain properties are obtained in this ceramic because sufficient domain switching can easily be achieved. The high dielectric constant can be further elevated after poling this ceramic due to the E-induced multiphase transitions. Dynamic piezoelectric measurement reveals that the dynamic piezoelectricity can reach to ∼740 pC/N, which is much higher than the static value (∼620 pC/N) of poled BTS–0.15BCT ceramic. However, the converse piezoelectric coefficient will decrease at high E, because of the quick decrease in dynamic dielectric response caused by clamped polarization at high E. All the results demonstrate that phase-coexistence BT-based ceramic shows electric field-related properties due to the soft structure, whereas it cannot be observed in BT ceramic with stable phase structure and large domains. This work reveals the evolution difference and structure origin of electrical properties in BT-based piezoceramics with different phase structures.     

Peculiar dielectric properties of (1-x)(K,Na)(Nb,Sb)O3−x(Bi,Na)ZrO3 ceramics

In spite of the significance from both scientific and technological viewpoints, systematical studies on the dielectric spectra of (K,Na)NbO₃-based lead-free ceramics particularly in the poled state had been scarcely performed so far. In this study, the compositional series of (1-x)(K_0.48Na_0.52)(Nb_0.96Sb_0.04)O₃?x(Bi_0.50Na_0.50)ZrO₃ ceramics were chosen representatively to shed more light on the characters of dielectric properties. All the ceramics in the unpoled state show dielectric spectra of large dispersion with the relaxational characteristic frequency higher than the measured upper limit of 60 MHz at room temperature. Additional resonance peaks due to the electromechanical coupling of piezoelectric effect appear and are accompanied by a large step-like reduction of dielectric permittivity ε′ in the dielectric spectra after poling. An abnormal phenomenon that poling induces the increase of low-frequency ε′ occurs in those ceramics with x ≥ 0.04 at room temperature, and is confirmed to associate closely with the orthorhombic-tetragonal and rhombohedral-orthorhombic polymorphic phase transitions. Further study of domain structure indicates that the origin of this abnormal phenomenon should be ascribed to the enhancement of domain-wall mobility because of the large reduction of domain-wall density due to the poling.     

Structure and composition of surface depletion layers in poled aluminosilicate glasses

Thermal poling processes can be used to form modified surface layers on glass that, under ion-blocking electrode conditions, are depleted of virtually all network-modifying cations relative to the network-forming species. During this process, many outstanding questions remain as to the structure of these layers and how it may vary between glasses of different “parent” composition, with important implications for resultant surface properties and industrial applications of this technology. This phenomenon of depleting modifiers is particularly difficult to rationalize in aluminosilicate glass compositions, where—in the parent glass—aluminum ions are predominantly present as cation-charge-compensated [AlO4]⁻ tetrahedra prior to poling. Here, we present results of a detailed investigation into the surface depletion layers formed across a wide range of ternary sodium aluminosilicate (NAS) glasses, applying a host of surface-sensitive spectroscopy methods to directly interrogate the resulting composition and structure within the Na-depleted, anode-side surface layers. The desired depletion layers were successfully formed on all of the NAS glasses attempted, all showing (a) near-complete depletion of alkali within 300-500 nm-thick layers on the anode-side surfaces, (b) thin zones of Al depletion with the Na-depleted layer, and (c) the absence of injected H⁺ ions that could serve as an alternative charge-compensation mechanism. These data essentially confirmed a true binary Al₂O₃–SiO₂ composition inside the depletion layers. However, no significant structural dependence was found as a function of parent glass, where initial compositions ranged from peralkaline to charge-balanced. Importantly, TEM imaging showed the depletion layers to be fully amorphous and homogeneous (not phase-separated) at the nanoscale, despite final compositions in the range of 5-33 mol% Al₂O₃—a composition space notoriously prone to phase-separation if prepared by conventional melting. Within the depletion layers, ELNES and TEY-XANES evidence is shown for retention of Al in a 4-coordinated state, along with XPS data indicating elimination of non-bridging oxygen. Taken as a whole, our results indicate a highly-connected aluminosilicate network, most likely with a relatively high concentration of 3-coordinated oxygen—or O “triclusters”—as a plausible means of charge-compensating 4-coordinated Al in the absence of Na⁺ or H⁺. The combined results of this work provide convincing new evidence for unique glass structures within the depletion layers not achievable through analogous melt pathways, with important implications for surface properties.     

Poling effect on optical and dielectric properties of Pr3+-doped Na0.5Bi0.5TiO3 ferroelectric single crystal

In recent years, with increased environmental awareness, more and more research has been carried out for lead-free ferroelectric materials. Among such materials, Na_0.5Bi_0.5TiO₃ (NBT) single crystal has become a material of interest due to its high Curie temperature. In this study, Pr-doped NBT crystals were prepared and poled along different crystal orientations. The effects of different crystal orientations and poling on the optical properties of Pr-doped NBT crystals were investigated. The optical transmission of the crystal decreases after poling along the [001] orientation and increases after poling along the [111] orientation. The emission and excitation spectra show that the poled process enhances the crystal luminescence. The dielectric constant dependence on temperature for different crystal orientations was measured. The domain structure was measured to explain the changes in the optical properties. The optical properties of a Pr-doped NBT single crystal were modulated by poling along different crystal orientations, which is expected to improve the performance of optoelectronic devices based on such materials.     

A new poling method for piezoelectric ceramics with thick film

The poling process plays an important role in the interaction with the crystal structure in a number of ways to obtain ferroelectricity and piezoelectricity. However, many factors influence the effectiveness of poling process. In the conventional poling process, electric field is applied to the ceramics via the metal electrode. The drawback of conventional poling method is the occasional occurrence of fracture and crack due to subjection to high electric voltage. In this study, a new poling method by using ITO (Indium Tin Oxide) glass for piezoelectric ceramics with thick film is proposed. The constraint of applying high electric field has been overcome and is verified with the use of energy level concept. As compared to conventional method, using ITO for poling will preserve better performance via various experimental testing.     

Theoretical estimation of dielectric loss of oxide glasses using nonequilibrium molecular dynamics simulations

To theoretically explore amorphous materials with a sufficiently low dielectric loss, which are essential for next-generation communication devices, the applicability of a nonequilibrium molecular dynamics simulation employing an external alternating electric field was examined using alkaline silicate glass models. In this method, the dielectric loss is directly evaluated as the phase shift of the dipole moment from the applied electric field. This method enabled us to evaluate the dielectric loss in a wide frequency range from 1 GHz to 10 THz. It was observed that the dielectric loss reaches its maximum at a few THz. The simulation method was found to qualitatively reproduce the effects of alkaline content and alkaline type on the dielectric loss. Furthermore, it reasonably reproduced the effect of mixed alkalines on the dielectric loss, which was observed in our experiments on sodium and/or potassium silicate glasses. Alkaline mixing was thus found to reduce the dielectric loss.     

A new method for recording images in glasses

A new method for recording images in alkali silicate glasses preliminarily subjected to ion exchange in a salt melt containing silver ions is proposed. The method is based on the process of glass poling followed by heat treatment in a hydrogen atmosphere. The use of the electrode (anode) with a relief surface pattern results in the formation of an amplitude imprint (image) of this pattern under the glass surface. A trial glass sample with the amplitude pattern of the surface relief of a coin has been produced.