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Outgassing of internal materials is one of the main factors that cause vacuum deterioration of low-light-level image intensifiers and shorten their lifetime (especially storage lifetime). To perceive the attenuation mechanism of the vacuum degree of image intensifiers from the microscopic view, the outgassing characteristics of lead silicate glass used for the fabrication of microchannel plates (MCPs), which are the core components of image intensifiers, were numerically simulated by giant canonical Monte Carlo and molecular dynamics methods. A glass structure model of the third-generation MCPs was constructed, and the diffusion coefficients and molecular motion trajectories of hydrogen, carbon dioxide, carbon monoxide, water vapor, oxygen, and methane gases, together with their outgassing rates and cumulative outgassing amounts, were calculated based on the condensed-phase optimized molecular potentials for atomistic simulation studies force field. The calculation results show that the rising temperature of MCP glass augments the diffusion coefficients of these gases, which makes the outgassing rates increase in the initial stage but then decrease relatively quickly. Among these six kinds of gas molecules, hydrogen molecules have the largest skip distance and the highest diffusion coefficient because MCP glass can supply more effective diffusion paths for the gas molecules with a relatively small size. When an MCP glass lies in vacuum, first, the cumulative outgassing amounts of various gases from it increase rapidly and then gradually reach stable values, and the cumulative outgassing amount of hydrogen tends to reach a stable value faster than that of other gases due to its highest diffusion coefficient. [ABSTRACT FROM AUTHOR]

The dielectric and transport properties of Ba(Fe0.5Nb0.5)O3 ceramics have been investigated in a temperature range of 140-300 K and a frequency range of 1 Hz-10 MHz. The temperature dependence of bulk dc conductivity does not feature an Arrhenius behavior, but indicates a variable-range-hopping mechanism. The observed low temperature relaxation can be perfectly described by a polaronic model, which indicates that the dielectric relaxation is intimately related to the hopping motion caused by localized charge carriers. [ABSTRACT FROM AUTHOR]

A synergetic effect of Li/Nd at the A site and W/Mn at the B site co-substitution on electrical properties of calcium bismuth niobate (CaBi2Nb2O9, CBNO)-based ceramics is proposed in this paper. CBNO primarily shows mixed p-type and ionic conduction due to a trace of oxygen vacancies (VO••). Both bulk resistivity (ρb) and activity energy (Ea) for conduction are dramatically increased by the co-substitution in Ca0.92(Li1/2Nd1/2)0.08Bi2Nb2−x(W3/4Mn1/4)xO9 [CBNO-LN-x(WM), x = 0–0.02]. Consequently, the modified compositions almost show an intrinsic conducting mechanism due to a significant suppression of the VO•• concentration. Furthermore, the synergetic effect of Li/Nd at the A site and W/Mn at the B site greatly improves the piezoelectricity coefficient (d33), which is up to ∼21.1 pC/N in the optimized composition [CBNO-LN-10(WM)]. This combined with a high Curie temperature (TC = ∼946 °C) and high resistivity indicates that CBNO-LN-10(WM) is a good promising material in high-temperature piezoelectric applications. [ABSTRACT FROM AUTHOR]

Low frequency dielectric dispersion behavior of the indium doped cadmium zinc telluride single crystal has been investigated. The temperature dependent of dielectric loss shows a broadening peak at high temperatures, which is attributed to thermally activated relaxation process. The large dielectric permittivity can be attributed to the influence of the dc conductivity and the predominance of the dc conduction in low frequency region overshadows the true behavior of the imaginary part of dielectric permittivity. The contribution of dc conduction and ac conduction has also been studied. A polaron theory indicates that the dielectric relaxation of the indium doped cadmium zinc telluride crystal at high temperature is associated with the hopping localized cadmium vacancies and telluride antisites defects. The hopping energy increases from 1.204 eV at 499 K to 1.267 eV at 534 K monotonically, which is close to the thermal activation energy 1.541 eV and dc conductivity activation energy 1.239 eV. [ABSTRACT FROM AUTHOR]

Ferroelectric ceramics SrBi2-xLaxNb2O9 (SBLNO) were prepared by a solid state reaction process. X-ray diffraction analysis indicated that single phase layered perovskites were obtained. The maximum dielectric permittivity peak broadened gradually with the lanthanum content increasing indicated that the phase transition from normal ferroelectrics to relaxorlike ferroelectrics occurs in SBLNO. The modified Curie–Weiss (CW) law was used to describe the relaxor behavior of SBLNO ceramics. The relaxation indication coefficient (γ) was estimated from a quadratic fit of modified CW law and was found to be 1.71 and 1.72 for SBLN20 and SBLN30 specimens, respectively. The substitution of La3+ ions for Bi3+ ions in the Bi2O2 layers resulted in a shift in the Curie point to lower temperature and an increase in remanent polarization and electrical field-induced strain. The maximum strain for SBLN30 specimen was found to be about 2.5×10-5 at the 5 MV/m. The nature of relaxor behavior of SBLNO is attributed to the cationic disordering at nanoscale on A site by the La3+ substituted Bi3+ of Bi2O2 layers. [ABSTRACT FROM AUTHOR]

The temperature and frequency dependences of dielectric properties of barium strontium titanate [Ba0.85Sr0.15TiO3 (BST15)] ceramics have been investigated. The dielectric relaxation behavior above 180 °C was observed in BST15 ceramics with broad dielectric peaks. The contribution of dc conduction and universal dielectric response to the relaxation has been studied. In contrast to typical ion conductor such as La2Mo2O9, the extent of dielectric dispersion shows the similar temperature dependence characteristic. Polaron theory indicates that the relaxation in BST15 ceramics at high temperatures is associated with the hopping localized oxygen vacancies. [ABSTRACT FROM AUTHOR]

The temperature dependence of dielectric permittivity was investigated for the barium zirconium titanate solid solution system [BZT, Ba(ZrxTi1-x)O3 0.25≤x≤0.5]. The dielectric relaxation behavior was observed in these ferroelectrics with diffused phase transition. In contrast to the canonical relaxors such as Pb(Mg1/3Nb2/3)O3, the diffused phase transition of BZT could not be well described by the popular modified Curie–Weiss law. Quasiferroelectric state theory was introduced to explain the dielectric results of the BZT relaxors. [ABSTRACT FROM AUTHOR]

Dielectric properties, microstructures, and phase transition behaviors of α and β phases of CaxBa1-xNb2O6 (x=0.22, 0.30, and 0.38) ceramics were investigated. All the three compositions had partially filled tungsten-bronze structure (TTB) and relatively high Curie temperatures (up to 345 °C) compared with Sr1-xBaxNb2O6. The α phase exhibits unambiguously a diffused phase transition, while the β phase is associated with an incommensurate phase and needs to be further studied. The dielectric and ferroelectric properties of CaxBa1-xNb2O6 ceramics were strongly processing-dependent. A mechanism was proposed to explain the grain growth behavior of TTB ceramic niobates. [ABSTRACT FROM AUTHOR]

The perovskite structure of Pb(Zn[sub 1/3]Nb[sub 2/3])O[sub 3] (PZN) ceramics was stabilized by adding a Ti-rich side tetragonal Pb(Zr[sub 0.47]Ti[sub 0.53])O[sub 3] (PZT) across the morphotropic phase boundary (MPB). The 0.5 PZN–0.5 PZT specimen was found to have a two-phase zone, having a high piezoelectric coefficient, d[sub 33] (430 pC/N), an electromechanical coupling factor, k[sub p] (0.67), a field-induced strain, S (0.24% at 2 kV/mm), and a remnant polarization, P[sub r] (27 μC/cm2). A phase transition from a rhombohedral to tetragonal phase occurred when a relatively low electrical field was applied to the specimen. This transformation occurred only when the rhombohedral phase coexisted with an equal amount of the tetragonal phase of the perovskite structure. Small rhombohedral domains, which were present around the relatively large tetragonal domains, transformed as a result of the applied field. The excellent electromechanical properties at the MPB composition are attributed to this phase transition in the PZN based ceramics. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

To improve the electron-induced secondary electron emission (SEE) properties of MgO/Au composite film, the strategy of Al doping in the MgO surface layer is adopted and investigated. For an MgO/Au film, Al doping in its MgO surface layer results in a slight increase of its grain size as well as a reduction of its surface roughness according to microstructure characterizations and also causes the decreases of both the band gap and work function of MgO crystal on the basis of the first-principles calculations, all of which have a close relationship with the improvement of secondary electron yield (SEY) demonstrated by the SEE measurement. An MgO/Au film including an Al-doped MgO surface layer with a doping ratio of 4.4% has an SEY of 4.7 with an increase of 14.6% at a primary electron energy (Ep) of 200 eV and the maximum SEY of 10.4 with an increase of 8.3% at Ep of 1100 eV in comparison with an MgO/Au film including an undoped MgO surface layer. [ABSTRACT FROM AUTHOR]

Double-loop-like characteristic was detected in acceptor Aurivillius ceramic, (Na,Bi)0.47(Li,Ce)0.03Bi2Ta1.97Sc0.03O8.97 (NBTO-LiCeSc-0.03) due to the restoring force provided by defect polarization (PD). The PD was associated with non-centric distributing defect dipoles [(ScTa″-VO••)×], which was verified by impedance spectroscopy measures. Interestingly, the PD could be reoriented with high external electric field at very low frequency, which contributed to the significant enhancement of the polarization of NBTO-LiCeSc-0.03. Air or O2 annealing led to the degradation of the polarization owing to high leakage current and the strong 'pinning' effects of space charge and charged defect complexes [e.g., (ScTa″-OO•)′]. [ABSTRACT FROM AUTHOR]

The Vögel-Fulcher (VF) equation ω=ω0 exp[-Ea/kB(Tm-Tf)] was frequently used to describe the dielectric relaxation of relaxor ferroelectrics where ω is the probe frequency at the peak temperature Tm of either the real or imaginary parts of the dielectric constant. We revisited this relation in a typical relaxor lead magnesium niobate and found that the parameters obtained were not physically meaningful. Meaningful results can only be obtained by fitting the VF relation on the characteristic relaxation time τc, whose temperature dependence can be obtained from the Cole-Cole model. The freezing temperature we obtained is 230 K, below which τc becomes temperature independent. [ABSTRACT FROM AUTHOR]

The piezoelectric response in Cd0.9Zn0.1Te (CZT) semiconductor single crystals has been investigated by analyzing room temperature impedance spectra. The polarization is significantly influenced by light illumination. A slow relaxation process of the piezoelectric response has been observed with a relaxation time of 37 s, which is comparable to the discharge current results. The frequencies for piezoelectric resonance and antiresonance can be tuned to lower values when a bias field is applied and can be recovered when the bias field is removed. These phenomena may be universal for ferroelectric semiconductors and can be explained by a slow relaxation model in dielectrics. [ABSTRACT FROM AUTHOR]

Transmission properties of a layer of split-ring resonators (SRRs) are investigated experimentally in free space with the propagation direction of the electromagnetic field perpendicular to the SRR-patterned substrate. It is shown that the response frequency of SRRs is independent of the measured distance. In addition, the qualitative change from electric resonance of SRRs to magnetic resonance with the variation of angle between electric field and the symmetric axis of SRR is presented. The results suggest a simple way of obtaining magnetic resonance of SRRs, even left-handed behavior. [ABSTRACT FROM AUTHOR]

A method to simultaneously measure the longitudinal (d[sub 33]) and transverse (d[sub 31]) piezoelectric coefficients of a lead zirconate titanate (PZT) thin film was developed. This system was based on the pneumatic loading method but was modified to monitor the radial strain when a pressurized gas was introduced into the chamber. The results of the bulk piezoelectric material measured by this system coincided with that measured by both the Berlincourt method and the resonance method. The effective d[sub 33] and the real d[sub 31] of the PZT thin film fabricated by the sol-gel multiple coating method, and poled at 300 kV/cm were 125 and -60 pC/N, respectively. The real d[sub 33] estimated upon considering the constraints by the silicon substrate was 180 pC/N. [ABSTRACT FROM AUTHOR]

Electrical conductivity of YMnO3 in O2, air, and N2 has been investigated by impedance spectroscopy. Within the investigated temperature range, three types of electrical conductivity were distinguished. Below 300 °C, the conductivity is dominated by p-type conductivity, while between 300 and 500 °C, the conductivity is in the so called saturation region. Above 500 °C, n-type conductivity occurred, probably due to the loss of oxygen. The air-processed YMnO3 is characterized by the presence of mixed Mn3+/Mn4+ and electrical heterogeneous structure, which are responsible for both, dielectric anomaly observed between 200 and 300 °C and nonlinear behavior under high electric field. [ABSTRACT FROM AUTHOR]

Annealing atmosphere effects on domain structures and electrical properties of Pb[(Zn[sub 1/3]Nb[sub 2/3])[sub 0.5](Zr[sub 0.47]Ti[sub 0.53])[sub 0.5]]O[sub 3] (PZN–PZT) ferroelectric materials were investigated. The PZN–PZT specimens were annealed in argon, air, oxygen, and PbZrO[sub 3] atmospheres after being sintered at 1100 °C in air. The as-sintered specimens were composed of large plate-like domains. When the specimen was annealed in flowing oxygen atmosphere for 8 h at 960 °C, the domains were refined into fine twin-like domains; whereas when the specimen was annealed in argon atmosphere, the domains were modified into needle-like structures. These modifications to the domain structures have a strong effect on the electromechanical properties of this material. The formation and redistribution of lead and oxygen vacancies during thermal annealing were responsible for those variations in domain structures and electrical properties. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]