Polarization and Conduction Mechanism in Mixed-Alkali Glasses

Thermally stimulated polarization and depolarization current (TSPC/TSDC) measurements on mixed alkali (Li-Na) silicate glasses show two TSDC peaks along with a dc conduction current at high temperatures, similar to single-alkali silicate glasses. The activation energies for the two TSDC peaks and for dc conduction increase with the addition of a second alkali. The first TSDC peak does not change in size but the second becomes substantially smaller when the second alkali is added. The reduction in size of the second TSDC peak correlates well with the reduction in the dielectric loss hi mixed-alkali glasses. A model is proposed to account for the behavior of the two TSDC peaks.     

Electrical Condultion and Polarization in Lead Silicate Glasses

Thermally stimulated polarization and depolarization current (TSPC/TSDC) and dc conductivity measurements on a series of lead silicate glasses were made between −196° and 190°C. The general composition of the glasses was xPbO·(100 − x )SiO₂, where x = 30, 40, 45, 50, and 65. The dc conductivity exhibits a monotonic increase with increasing PbO content. For x > 45, the rise in conductivity with increasing PbO content is much less than for x < 45. Two TSDC peaks have been observed in all the glasses. The smaller of the two TSDC peaks, occurring at lower temperatures, increases linearly in size with increasing concentrations of PbO. The high-temperature TSDC peak does not saturate from −196° to 190°C. Direct current conductivity in these glasses is ionic and due to the motion of Pb²⁺ ions. The behavior of the low-temperature TSDC peak is consistent with the hypothesis that it is caused by short-range motion (orientational polarization) of Pb²⁺ ions. The origin of the high-temperature TSDC peak is tentatively attributed to space charge polarization of Pb²⁺ ions.     

Thermally Stimulated Currents and Alkali-Ion Motion in Silicate Glasses

The thermally stimulated polarizatioddepolarization (TSPC/TSDC) current technique is used to investigate alkali-ion motion in silicate glasses. lbo TSDC peaks are observed in all these glasses along with the dc conduction current at high temperatures. The low-temperature TSDC peak magnitude is essentially constant, but the second TSDC peak magnitude varies with the type of alkali ion present in these glasses. Based on a proposed model, the two TSDC peaks are interpreted in terms of the localized alkali-ion motion around the nonbridging oxygen ion and through the limited conduction pathways, respectively.     

Sodium Motion in Phase-Separated Sodium Silicate Glasses

The thermally stimulated polarization and depolarization current (TSPC/TSDC) technique was used to study Na^plus; ion motion in phase-separated silicate glasses containing between 10.3 and 20 mol% Na₂O. Generally, two TSDC peaks and a high-temperature background (HTB) current were observed. The two TSDC peaks were attributed to different types of Na^plus; motion, i.e. a short-range reorientation process and a longer-range translational motion. Changes in the microstructure affected only the size of the larger TSDC peak located at higher temperatures.     

Thermally Stimulated Polarization and Depolarization in Halogen-Containing Lead Silicate Glasses

Thermally stimulated polarization and depolarization current (TSPC/TSDC) measurements were made on lead halide silicate glasses having compositions (65 − x )PbO· x PbX₂·35SiO₂ where x = 0, 0.1, 2, 10 and X = F, CI, Br, and I. The addition of halogen ions to lead silicate glasses gives rise to a new high-temperature TSDC peak in the vicinity of the peak previously observed in binary lead silicate glasses. The integrated area of the new peak is dependent on the amount and type of halogen ion present in the glass and does not saturate in the temperature range of our measurements. This new peak is attributed to space charge polarization of halogen ions.     

Thermally stimulated depolarization currents in poly (ethyleneterephthalate‐ran‐p‐hydroxybenzoates)

Thermally stimulated polarization (TSPC) and depolarization currents (TSDC) are measured on polyethylene terephthalate (PET) copolymerized with p‐hydroxy benzoic acid (PHB). These systems are important since they comprise components of many commercial polymer liquid crystals (PLCs). There has been some speculation about the origins of the multiple transition peaks in TSDC of PLCs and secondary peaks have frequently been designated as resulting from Maxwell‐Wagner interphase polarization. The applicability of this designation for main chain PLCs has been investigated. TSDC as a function of field strength and window polarization has been conducted and the transitions have been identified as glass transition peaks as opposed to space charge relaxations. A comparison of the TSDC current versus the polarization current (TSPC) reveals that TSPC is not generated for transitions associated with the PHB component.     

Relaxation processes in barium strontium titanate glass-ceramics by thermally simulated depolarization current

Thermally stimulated depolarization current (TSDC) experiments were carried out to investigate the effect of polarization temperature on different relaxation processes in barium strontium titanate glass-ceramics. It was found that all the TSDC curves are composed of four relaxation peaks. From the characteristics of peak temperature and peak current intensity with various polarization temperatures, the origin of these four peaks are identified as from defect dipole orientation, charge carrier detrapping, in-crystal oxygen vacancy migration, and trans-interface oxygen vacancy migration respectively. In addition, both the dipole concentration and trap density for the glass-ceramic samples were estimated.     

Internal Friction of Simple Alkali Silicate Glasses Containing Alkaline-Earth Oxides: I, Experimental Results

The internal friction of simple alkali silicate glasses to which systematic alkaline-earth oxide additions were made was investigated. These additions produced two significant results: (1) The two peaks previously reported in alkali silicate glasses were shifted to higher temperatures and decreased in height and (2) a third peak was found in some glasses which became more pronounced with increasing alkaline-earth oxide content. Internal friction measurements of alkali-free silicate and phosphate glasses also are described. In these glasses, peaks were present which closely resembled those found in glasses containing alkali.     

Polarization Response and Thermally Stimulated Depolarization Current of BaTiO3‐based Y5V Ceramic Multilayer Capacitors

Polarization response and thermally stimulated depolarization current (TSDC) of BaTiO₃‐based ceramic multilayer capacitors with Y5V specification were studied. The temperature dependence of dielectric behavior shows that as the dc electric field increases, the polarization response in the whole measurement range (from ?125°C to +350°C) is suppressed. As the temperature rises to about 250°C, dielectric loss significantly increases and has a dependence on dc electric field, due to the leakage behavior at high temperature. According to the hysteresis loops, the calculated electrostatic energy density and energy efficiency are also closely related to polarization‐electric field. Utilizing a fixed measuring polarization condition, two TSDC relaxation peaks are observed and both are associated with oxygen vacancies. It is demonstrated that the weak peak originates from the in‐grain migration of oxygen vacancies and the strong peak with high relaxation temperature is caused by the across grain‐boundary oxygen vacancies. The activation energy estimated for the relaxation of oxygen vacancies across grain boundaries is about 0.78 eV. The main contribution for the leakage behavior is from the across grain‐boundary relaxation of oxygen vacancies. With increasing of temperature and electric field stress, the extrinsic oxygen vacancy defects show more fluent migration, which eventually leads to the resistance degradation and breakdown.     

Characterization of castor oil based polyurethane films prepared with N‐methyl‐2‐pyrrolidinone as a solvent

Molecular mobility in castor oil based polyurethane was investigated with thermally stimulated depolarization current (TSDC) measurements and alternating‐current (ac) dielectric relaxation spectroscopy. Three peaks could be observed in TSDC thermograms from 173 to 373 K. The relaxation located at 213 K could be attributed to the change in the molecular chain due to the interaction between the isocyanate and the solvent, and it was well fitted with the Vogel–Fulcher–Tammann equation. The other two peaks were located at 274 and 365 K and could be attributed to interfacial polarization and space charge, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 746–749, 2005     

Ion Depletion of Glass at a Blocking Anode: I, Theory and Experimental Results for Alkali Silicate Glasses

A theory is presented for the ion depletion of glass beneath a blocking anode. The theoretical model is based on the assumption that the alkali ions in an alkali silicate glass have a much greater mobility than the nonbridging oxygen ions in the alkali-depleted region. In this case, the dc conduction properties of the glass are determined by the motion of the uncombined oxygen ions in the depleted region. Expressions are derived for the spatial variation of the uncombined oxygen ions and for the current-voltage relations in the high- and low-field limits. In the high-field limit, the theory predicts that the current will vary exponentially with the voltage; this behavior is shown in sodium silicate glasses.     

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.     

Study of electrical properties for albumin/ poly(vinyl alcohol) blends

Thermally stimulated depolarization current (TSDC), d.c. electrical conductivity (σ), and current–time characteristic techniques were used to study electrical polarization and conduction mechanisms for pure poly(vinyl alcohol) (PVA) and 2.5, 5, 10, 12, 15, and 20 wt % albumin content in PVA thin films. The TSDC spectrum for PVA revealed the existence of two broad peaks, while the blend samples show only one broad peak with a shoulder in the high‐temperature side. The existence of this current maximum was analyzed and discussed in terms of dipole‐orientation and space‐charge phenomena. Quantitative analysis was carried out to determine the thermal activation energies of the conduction process, drift mobility, and carrier concentration. The crystallinty of the PVA matrix was enhanced by the addition of albumin, as indicated by X‐ray diffraction and differential scanning calorimetry (DSC) measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1748–1757, 2003     

Characterization and thermally stimulated depolarization current studies of rhodamine-dye-doped poly(acrylonitrile–butadiene–styrene) films

IR and UV-absorption spectra, and the thermally stimulated currents of pure and Rhodamine-6G-doped poly(acrylonitrile–butadiene–styrene) (Rhdoped ABS) films were investigated. Structural characteristics could be specified from these techniques. Both IR and UV-absorption studies revealed a modification of the structure of ABS on blending with Rhodamine 6G: Rh molecules are partially dispersed in the ABS matrix and partially attached as side groups to the ABS backbone. Thermally stimulated depolarization current (TSDC) studies confirmed this result. The results revealed that incorporation of Rh 6G in ABS locks the dipole in the ABS matrix after electric poling. The TSDC spectra have been found, depending on the polarization temperature, to be characterized by three peaks. The phenomenon of the existence of these current maxima is discussed and analysed in terms of dipolar and ionic relaxations.     

硅酸钠预处理对镀锌层稀土镧盐转化膜耐蚀性的影响

对热镀锌钢板先进行硅酸钠(水玻璃)预处理再镧盐钝化,以进一步提高镧盐转化膜的耐蚀性.用扫描电镜、能谱仪、盐雾腐蚀试验、塔菲尔极化曲线等方法研究了硅酸钠预处理对热镀锌层镧盐转化膜微观形貌和耐蚀性的影响.结果表明,硅酸钠预处理使得镧盐转化膜成膜均匀,膜层增厚且耐蚀性明显提高.通过正交试验得到最佳工艺为:先在室温下于0.5 ...     

A thermally stimulated depolarization current study of polymers in the glass transition region

The low‐frequency dielectric properties of a number of polymers, composites and blends have been studied using a thermally stimulated depolarization current (TSDC) apparatus that was designed and constructed in‐house. The TSDC technique can be used to determine the glass transition of a polymer sample. This TSDC glass transition temperature has been shown to be very similar to that obtained from differential scanning calorimetry (DSC). The actual difference between these two values depends on the heating rates used with each technique, however. TSDC data can also be combined with AC dielectric data to produce a data set, which possesses a very wide frequency range. Finally, individual TSDC relaxation peaks can be fit with the Williams‐Walts distribution function to obtain an estimate of their distributions. This is especially useful when studying polymer blends, but could also be utilized in the study of other systems.     

Annealing effect on chain segment motion and charge detrapping in polyamide 610

The chain segment motion and charge detrapping in polyamide 610 films have been investigated by means of thermally stimulated depolarization current (TSDC) and wide‐angle X‐ray diffraction. There are three current peaks (namely α, ρ₁, and ρ₂ peaks) in the TSDC spectra above room temperature. α peak is attributed to a dipole relaxation by the motion of chain segments ρ₁ peak is caused by space charge trapped in amorphous phase and the interphase between crystalline and amorphous phases, and ρ₂ peak is brought about by space charge trapped in crystalline phase. By analyzing the characteristic parameters of these peaks, it is found that annealing induces the decrease of chain segment mobility and promotes the creation of structural traps in polyamide 610. The decrease of chain segment mobility in amorphous phase makes intensity of α peak weak and activation energy increscent. The higher the annealing temperature, the higher the degree of crystallinity, the more the charge carriers trapped in crystalline phase. So, the increase of degree of crystallinity makes intensity of ρ₂ peak strong and increases the stability of trapped charge in the crystalline phase. The increase of annealing temperature makes intensity of ρ₁ peak strong and decreases the stability of trapped charge in the amorphous phase and interphase. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ion migration study in acid-leached soda–lime–silica glass by thermally stimulated depolarization current analysis

Ionic conductivity in silicate glasses is a major issue in the energy sector due to its detrimental effect on electric energy generation and storage and has received increasing attention over the past years. In this study, surface modification of soda–lime–silica (SLS) float glass via acid-leaching treatment (pH 1) was implemented to understand the impact on ionic transport. The acid-leaching treatment created a sodium-depleted “silica-like” structure in the near-surface region with depths of 110 ± 20 nm for the air-side and 93 ± 2 nm for the tin-side of the SLS glass. Using the thermally stimulated depolarization current technique, two thermally activated relaxation peaks were found to be associated with different ion migration mechanisms. The first peak (P1) with activation energy of ∼0.85 eV was attributed to dc conduction of Na⁺ ions through the glass bulk. A second overlapping peak (P2) at a higher temperature was found to be related to a more limited Na⁺ ion migration through the acid-leached structure, due to H⁺ conduction, or a coupled contribution of both mechanisms.     

Molecular mobility of CU(II)-containing liquid crystalline ionomers: dielectric relaxation and thermally stimulated depolarization currents

Molecular mobility of functionalized liquid crystalline (LC) copolymer (P1) containing mesogenic cyanobiphenyl groups and acrylic acid fragments (28%) as well as LC ionomers P2 (Cu 2.5() and P3 (Cu 7() with copper ions were studied by dielectric spectroscopy (DS) and by thermally stimulated depolarization current (TSDC) methods. For P1-P3, the frequency dependences of dielectric losses and temperature dependences of depolarization current were obtained and four relaxation processes γ₁, β, α, and δ were found. For each of them a molecular mechanism was proposed. Moreover, for P1, P2, and P3, at high temperatures the TSDC global curves indicate the peak of depolarization current, which has no analogue in the dielectric spectrum. For P1 this peak is a ρ-process of low intensity. For P2 and P3 ionomers the intensity and temperature position of the high temperature peak increase as compared to those of P1. The mechanisms of the high temperatures peak for the P2 and P3 systems containing copper ions were attributed to the free space charge polarization and to the dipole polarization process of polymer chains included in ionic associates (multiplets). There is good correlation between the peak temperature positions obtained from the global TSDC spectrum at equivalent frequency and those obtained from DS.     

Relaxation phenomenon of poly(vinyl alcohol)/sodium carboxy methyl cellulose blend by thermally stimulated depolarization currents and thermal sample technique

The dipolar relaxation in poly(vinyl alcohol) (PVA), sodium carboxy methyl cellulose (NaCMC_s), and their blends were studied using a thermally stimulated depolarization current (TSDC) technique. The mutual effects of polarization conditions such as heating rate, poling temperature, time, and field on the properties of TSDC were investigated. Quantitative analysis of the experimental data is given in terms of dipolar and space charge polarization. A thermal sampling (TS) technique was applied to decompose the complex relaxations in individual polymers and their blend of 0.5/0.5 wt/wt into its normal distribution components. The activation energy of TS‐formed electrets was determined by fitting the experimental curve to Bucci and Fieschi equations. Peak parameters such as activation energy and preexponential factor τ₀ were obtained. A linear relationship between the activation energy and logarithm of the preexponential factor was found, thus confirming operation of the compensation law. In addition, by using the Eyring equation of the rate theory, the activation enthalpy ΔH^≠ and the activation entropy ΔS^≠ were calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1342–1353, 2005