A transient method of measuring the water vapour permeability of packaging films I. Dynamic performance of a sorptive sensor

Principles of an analysis of the inertia of a sorptive sensor used for transient measurements of water vapour permeability through packaging films have been developed. The construction of the measuring cell and the method of measurement of water vapour permeation through packaging films have been readjusted to the developed principles. It is shown that the inertia of a sorptive sensor, defined as a difference Δ between measured signal value RH* and an estimated value of air relative humidity RH₁ close to the film surface in an input chamber can be described as a difference of exponential functions Δ = RH₀·[exp(−Aτ) − exp(−Bτ)]. The characteristic parameter determining the sensor inertia is the maximum delay time τ_m; the roots of the function Δ(τ) derivative. The theory and procedure for using τ_m for the iterative determination of water vapour permeability through packaging films based on analysis of the sorptive sensor inertia is presented.     

Non-dissipative decoherence for quantum carpets

Abstract

We describe decoherence for quantum carpets using a modelindependent formalism ruled by a characteristic time τ. We find that the rate of decoherence depends critically on the ratio between τ and τ_E = h/2σ_H. When τ/τ_E « 1 decoherence is very slow, while it becomes very fast for the opposite case. The rate of decoherence is described in terms of the fidelity function.     

Microstructure and microwave dielectric properties of low-temperature sinterable (1 − x)Ba3(VO4)2–xCaWO4 composite ceramics

Low-temperature-sintered Ba₃(VO₄)₂–CaWO₄ composite ceramics were prepared by cofiring mixtures of pure-phase Ba₃(VO₄)₂ and CaWO₄. The thermo-mechanical analysis revealed that the CaWO₄ in the composite ceramic can significantly promote the densification process and lower the sintering temperature to ~900 °C. The X-ray diffraction results indicated that Ba₃(VO₄)₂ and CaWO₄ phases coexist in the sintered ceramics, and no secondary phases can be detected in the composite, implying the good chemical compatibility between the two phases. The near-zero temperature coefficients of the resonant frequency (τ_f) could be achieved by adjusting the relative content of the two phases owing to their opposite τ_f values. The composite ceramics with 60 wt% CaWO₄ sintered at 900 °C exhibited desirable microwave dielectric properties of the quality factor Q × f ~ 37,000 GHz, dielectric constant ε_r ~ 12, and τ_f ~ ?1.4 ppm/°C.     

Tuning the temperature coefficient of resonant frequency for 8-layer twinned hexagonal perovskite Ba<Subscript>8</Subscript>ZnTa<Subscript>6</Subscript>O<Subscript>24</Subscript> ceramics

High-Q dielectric materials ilmenite MgTiO₃, columbite MgNb₂O₆ and cubic perovskite Ba₃NiTa₂O₉ with negative temperature coefficient of resonant frequency (τ _f ) were selected as candidates for compensating the τ _f of hexagonal perovskite Ba₈ZnTa₆O₂₄. X-ray diffraction data shows that Ba₈ZnTa₆O₂₄ coexists with Ba₃NiTa₂O₉ but is not compatible with MgTiO₃ and MgNb₂O₆ at high temperature. The τ _f for the mixed hexagonal/cubic perovskite Ba₈ZnTa₆O₂₄–Ba₃NiTa₂O₉ system is tunable via the temperature compensation effect and its quality factor may be improved via annealing the ceramics at high temperature to enhance the cation ordering in the cubic component. Permittivity ε _r  ~ 22–25, Q×f > 30,000 GHz and tunable τ _f within ±10 ppm/°C were achieved in the range of about 50–80 wt% Ba₃NiTa₂O₉ for the hexagonal/cubic perovskite composite Ba₈ZnTa₆O₂₄–Ba₃NiTa₂O₉ ceramics, which is suitable for the application as dielectric resonators and filters.     

A criterion of applicability of the parabolic heat conduction equation

A criterion (K _MCV) of applicability of the parabolic heat conduction equation to isotropic materials is proposed that quantitatively determines the conditional boundary between linear and nonlinear regimes of nonequilibrium thermodynamics in the one-dimensional formulation of some heat transfer problems. The criterion is related to the heat flux relaxation time τ_r. Once this characteristic time is known, the condition K _MCV = 0 implies validity of the parabolic heat conduction equation. If τ_r is unknown, the adequacy of the parabolic heat conduction model can be judged from the absence of a temporal variation of the K _MCV/τ_r ratio under the main condition that the heat source power is independent of the time.     

Low-temperature firing and microwave properties of TiO2 modified Li2ZnTi3O8 ceramics doped with B2O3

The low-temperature firing and microwave properties TiO₂ modified Li₂ZnTi₃O₈ ceramics with B₂O₃ addition have been developed. B₂O₃ addition could reduce the sintering temperature of Li₂ZnTi₃O₈ ceramics from 1,150 to 900 °C, which is attributed to the formation of liquid phases during the sintering process observed by SEM. The 1.5 wt% B₂O₃ doped Li₂ZnTi₃O₈ ceramics sintered at 900 °C have ε _r = 23.3, Q × f = 48,817 GHz, and resonant frequency τ _f  = ?15.35 × 10^?6/°C. Further, due to the compensating effect of rutile TiO₂ (τ_f  = 450 ppm/°C), the temperature coefficient of τ_f for with TiO₂ was adjusted to near zero value. The 1.5 wt% B₂O₃ doped Li₂ZnTi₃O₈ ceramics with 3 wt% TiO₂ dielectrics sintered at 900 °C exhibited the optimal microwave properties: ε_r = 25.9, Q × f = 46,487 GHz, and τ_f = ?0.35 ppm/°C.     

Temperature compensating microwave dielectric based on the (Mg0.97Co0.03)2(Ti0.95Sn0.05)O4–CaTiO3 ceramic system

The microstructures and the microwave dielectric properties of the (1 ? x)(Mg_0.97Co_0.03)₂(Ti_0.95Sn_0.05)O₄–xCaTiO₃ ceramic system prepared by the conventional solid-state route were investigated. (Mg_0.97Co_0.03)₂(Ti_0.95Sn_0.05)O₄ possesses high dielectric constant (ε_r = 14.23), high quality factor (Q × f = 188,760 GHz), and negative τ_f value (τ_f = ?55.48 ppm/°C) at 1,390 °C for 4 h. In order to achieve a temperature stable material, CaTiO₃, having a large positive τ_f value of 800 ppm/°C, was added to (Mg_0.97Co_0.03)₂(Ti_0.95Sn_0.05)O₄. Two phase system was confirmed by the X-ray diffraction patterns and the energy-dispersive X-ray analysis. Although the ε_r of the specimen could be boosted by increasing amount of CaTiO₃, it would instead render a decrease in the Q × f. By appropriately adjusting the x value in the (1 ? x)(Mg_0.97Co_0.03)₂(Ti_0.95Sn_0.05)O₄–xCaTiO₃ ceramic system, zero τ_f value can be achieved. A new microwave dielectric material, 0.91(Mg_0.97Co_0.03)₂(Ti_0.95Sn_0.05)O₄–0.09CaTiO₃ ceramic sintered at 1,390 °C had optimal dielectric properties (ε_r = 18.13, Q × f = 87,562 GHz, τ_f = 3.75 ppm/°C) which satisfied microwave applications in resonators, filters and antenna substrates.     

Control of temperature coefficient of resonant frequency in Ba4Sm9.33Ti18O54 ceramics by templated grain growth

A novel tuning method of temperature dependence of dielectric properties in Ba₄Sm_9.33Ti₁₈O₅₄ (BSmT) microwave material was demonstrated by texture engineering. Two kinds of grain-oriented BSmT ceramics were obtained using a templated grain growth technique. Highly fiber-textured ceramics were fabricated by tape casting of slurry with a mixture of 〈001〉-elongated BSmT template particles and fine-grained BSmT powder. On the other hand, partially grain-oriented ceramics were also obtained from the uniaxially pressed mixture of the template particles and the fine-grained powder. Orientation degree of sintered BSmT ceramics increased with a content of template particles. As compared with the specimen prepared by normal sintering technique, the textured ceramics displayed a large anisotropy in the dielectric properties, especially in the temperature coefficient of resonant frequency (τ_f). Consequently, near-zero τ_f was obtained in the textured ceramics with (hk0)-orientation degree of approximately 0.10 in the surface of the disk specimen. In addition, the τ_f could be controlled to a desired value from ranging −90 to +25 ppm/°C by adjusting the grain orientation in the specimen. Measurement of the temperature dependence of dielectric constant, which correlates with τ_f, revealed positive and negative behaviors for (hk0) and (001) textured BSmT ceramics, respectively. The tuning of τ_f was explained as a rule of mixture of dielectric anisotropy in BSmT.     

Low-temperature sintering and microwave dielectric properties of Li2TiO3 based ceramics

New low sintering temperature and temperature-stable low-loss ceramics based on Li₂TiO₃ with lithium zinc borate (LZB) glass and LiZnNbO₄ doping have been prepared by the conventional solid-state reaction route. The effect of LZB glass addition on the sinterability, phase purity, microstructure, and microwave dielectric properties of Li₂TiO₃ ceramics has been investigated. The XRD results suggest the presence of single Li₂TiO₃ phases for LZB glass-added Li₂TiO₃ ceramics. The addition of LZB glass can effectively lower the sintering temperature to 900 °C, and does not induce much degradation of the microwave dielectric properties. Typically, the 2.0 wt% LZB glass-added ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 23.2, Q × f = 38,909 GHz, and τ _f  = 30.1 ppm/°C. Meanwhile, LiZnNbO₄ compound is selected to tune the temperature coefficient of resonant frequency (τ _f ) to near zero. It is found that the 2.0 wt% LZB glass-added Li₂TiO₃ ceramics with 35 wt% LiZnNbO₄ sintered at 925 °C have good microwave dielectric properties of ε_r = 20.7, Q × f = 19,366 GHz, τ _f  = ?0.5 ppm/°C, which can find applications in microwave devices that require low sintering temperature.     

Microstructure and microwave dielectric properties of xSm(Mg0.5Ti0.5)O3–(1 − x)Ca0.8Sr0.2TiO3 ceramics

xSm(Mg_0.5Ti_0.5)O₃–(1 ? x)Ca_0.8Sr_0.2TiO₃ (x = 0.50–0.95) ceramics are prepared by a conventional solid-state ceramic route. The microstructure and microwave dielectric properties are investigated as a function of the x-value and sintering temperature. The single phase solid solutions were obtained throughout the studied compositional range. The variation of bulk density and dielectric properties are related with the x-value. Increasing sintering temperature can effectively promote the densification and dielectric properties of xSm(Mg_0.5Ti_0.5)O₃–(1 ? x)Ca_0.8Sr_0.2TiO₃ ceramic system. With the content of Sm(Mg_0.5Ti_0.5)O₃ increasing, the temperature coefficient of resonant frequency τ _f value decreased, and a near-zero τ _f could be obtained for the samples with x = 0.80. The optimal microwave dielectric properties with a dielectric constant ε _r of 30.1, Q × f of 115,000 GHz (at 8.0 GHz), and τ _f of 8.9 ppm/°C were obtained for 0.80Sm(Mg_0.5Ti_0.5)O₃–0.20Ca_0.8Sr_0.2TiO₃ sintered at 1,550 °C for 3 h, which showed high density and well-developed grain growth.     

Microwave dielectric properties and low temperature sintering of Ba3Ti4?x(Mg1/3Nb2/3)xNb4O21 ceramics with BaCu(B2O5) addition

Microwave dielectric ceramics of Ba₃Ti_4?x(Mg_1/3Nb_2/3)_xNb₄O₂₁ solid solutions (BTMNN-x, x?=?0–4) were prepared via the conventional solid-state reaction method. The X-ray powder diffraction analysis revealed that the BTMNN-x ceramics formed complete solid solutions with hexagonal structure. The dielectric constant (ε_r) and the temperature coefficient of the resonant frequency (τ_f) of BTMNN-x ceramics decreased with the increase of x, while the quality factor (Q?×?f) enhanced with increasing the substitution content. In addition, a small amount of BaCu(B₂O₅) (BCB) additive can effectively lower the sintering temperature of BTMNN ceramics. The 1.5?wt% BCB doped BTMNN-2 ceramics can be sintered at 950?°C and have good microwave dielectric properties of ε_r?=?50, Q?×?f?=?10,500?GHz and τ_f?=?18?ppm/°C, which makes it possible to be a promising candidate for mid-permittivity low temperature co-fired ceramic materials.     

Phase composition and microwave dielectric properties of (Zn,Ni)TiNb2O8 solid solution

The Zn_1?xNi_xTiNb₂O₈ (x = 0, 0.1, 0.2, 0.3, 0.4) ceramics were synthesized by the conventional solid-state reaction method. The crystal structure and microwave dielectric properties were investigated by XRD, SEM and dielectric measurements. The XRD patterns of Zn_1?xNi_xTiNb₂O₈ ceramics showed that (Zn, Ni)TiNb₂O₈ phase and (Ni, Zn)_0.5Ti_0.5NbO₄ phase were obtained. With the increase of sintering temperature and Ni content, the amount of the second phase [(Ni, Zn)_0.5Ti_0.5NbO₄] enhanced, resulting in the increase of dielectric constant and the decrease of Q × f value. Moreover, the temperature coefficient of resonant frequency (τ_f) shifted to a positive value with increasing Ni content. In conclusion, the excellent microwave dielectric properties were obtained for Zn_0.7Ni_0.3TiNb₂O₈ ceramics sintered at 1,125 °C for 4 h: ε_r = 41.36, Q × f = 31,760 GHz, τ_f = ?9.2 ppm/°C. Furthermore, to realize the zero value for τ_f, a proper adjustment of Ni doping and sintering temperature can be feasible in this system.     

Low temperature sintering and dielectric properties of Li2ZnTi3O8–TiO2 composite ceramics doped with CaO–B2O3–SiO2 glass

The effects of CaO–B₂O₃–SiO₂ (CBS) glass addition on the sintering temperature and dielectric properties of Li₂ZnTi₃O₈–TiO₂ (LZT) composite ceramics have been investigated. Due to the compensating effect of rutile TiO₂ (τ_f ≈ +450 ppm/ °C), the temperature coefficient of resonant frequency (τ_f) for Li₂ZnTi₃O₈ + 4 wt% TiO₂ with biphasic structure was adjusted to a value near zero. The pure LZT ceramics were usually sintered at high temperature of about 1,160 °C. It was found in our experiment that a small amount of CBS glass additives could effectively lower the sintering temperature of LZT ceramics to 900 °C. With increasing the content of CBS glass, both of dielectric constant (ε_r) and quality factor (Q × f) value decreased. Typically, the 1 wt% CBS glass added Li₂ZnTi₃O₈ + 4 wt% TiO₂ ceramic sintered at 900 °C for 4 h exhibited good microwave dielectric properties of ε_r = 26.9, Q × f = 23,563 GHz and τ_f = ?1.5 ppm/ °C, which made it promising for low temperature co-fired ceramics technology application.     

SiGe heterojunction bipolar transistor issues towards high cryogenic performances

The performances increase at low temperature make the SiGe HBT a masterpiece for cryogenic circuits. The time-progressive enhancement of f_T and f_MAX toward the THz frequency at room and at cryogenic temperatures is presented along with STMicroelectronics and IBM successive HBTs generations. The influence of the Ge content and graduality into the base is discussed, highlighting the keys for best high-frequency cryogenic operation. This is shown with eight different cases and addressed on f_T, f_MAX, the transit time, the minimum noise figure and the equivalent noise resistance.     

Effects of MnO2 doping on microstructure and microwave dielectric properties of Ba4.2Nd9.2Ti18O54–NdAlO3 ceramics

MnO₂ doped Ba_4.2Nd_9.2Ti₁₈O₅₄–NdAlO₃(13 wt%) (BNT–NA) microwave dielectric ceramics with the near zero τ _f and the wide range of sintering temperature were prepared by conventional solid state method. The effects of Mn⁴⁺ doping on the microstructures and microwave dielectric properties of BNT–NA ceramics were investigated. XRD patterns showed only a single BaNd₂Ti₅O₁₄ phase was identified in all samples and there was no second phase. The sintering temperature decreased from 1,380 to 1,320 °C as MnO₂ content increased from 0.1 to 0.9 wt%. The MnO₂ doped BNT–NA ceramics could be densified at a lower sintering temperature. The MnO₂ additive had a positive effect on lowing sintering temperature of BNT–NA ceramics. The τ _f varied from negative to positive with the increase of MnO₂. Excellent microwave dielectric properties were achieved in Ba_4.2Nd_9.2Ti₁₈O₅₄–NdAlO₃ ceramics doped with 0.3 wt% MnO₂ and sintered at 1,380 °C for 2 h: ε _r  = 66.5, Q × f = 13,948 GHz, τ _f  = 0.4 ppm/°C.     

Dielectric properties of a new ceramic system (1 − x)Mg4Nb2O9-xCaTiO3 at microwave frequency

The microstructures and the microwave dielectric properties of the (1 − x)Mg₄Nb₂O₉-xCaTiO₃ ceramic system were investigated. In order to achieve a temperature-stable material, CaTiO₃ (τ_f ∼ 800 ppm/°C) was chosen as a τ_f compensator and added to Mg₄Nb₂O₉ (τ_f ∼ −70 ppm/°C) to form a two phase system. It was confirmed by the XRD and EDX analysis. By appropriately adjusting the x-value in the (1 − x)Mg₄Nb₂O₉-xCaTiO₃ ceramic system, near-zero τ_f value can be achieved. A new microwave dielectric material, 0.5Mg₄Nb₂O₉-0.5CaTiO₃ applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant ?_r ∼ 24.8, a Q × f value ∼82,000 GHz (measured at 9.1 GHz) and a τ_f value ∼−0.3 ppm/°C.     

A new low-loss microwave dielectric using (Ca0.8Sr0.2)TiO3-doped MgTiO3 ceramics

The microwave dielectric properties and the microstructures of the (1-x)MgTiO₃-x(Ca_0.8Sr_0.2)TiO₃ ceramic system prepared by the conventional solid-state route were investigated. (Ca_0.8Sr_0.2)TiO₃ was employed as a τ_f compensator and was added to MgTiO₃ to achieve a temperature-stable material. Ilmenite-structured MgTiO₃ and perovskite-structured (Ca_0.8Sr_0.2)TiO₃ were coexisted and the two-phase system was confirmed by the X-ray diffraction patterns and the energy-dispersive X-ray analysis. Although the ε_r of the specimen could be boosted by increasing amount of (Ca_0.8Sr_0.2)TiO₃, it would instead render a decrease in the Q × f. The τ_f value is strongly correlated to the compositions and can be controlled through the existing phases. In fact, τ_f could be adjusted to a near-zero value by mixing 94 mole% MgTiO₃ and 6 mole% (Ca_0.8Sr_0.2)TiO₃. A dielectric constant (ε_r) of 21.42, a high Q × f value of 83,700 GHz (at 9 GHz) and a temperature coefficient of resonant frequency (τ_f) of − 1.8 ppm/°C were obtained for 0.94MgTiO₃-0.06(Ca_0.8Sr_0.2)TiO₃ sintered at 1300 °C for 4 h. It is proposed as a low-loss and low-cost dielectric material for microwave and millimeter wave applications.     

Microwave dielectric properties of Ba[(Zn1−xCox)1/3Nb2/3]O3 ceramics

Microwave dielectric ceramics of Ba[(Zn_1−xCo_x)_1/3Nb_2/3]O₃ (x=0–0.8) were prepared by solid-state reaction method. The microwave dielectric properties, such as dielectric constants, Q×f values and τ_f (temperature coefficient of resonant frequency) were studied as a function of compositions and sintering temperatures. The results revealed that the dielectric constant and Q×f value decrease almost linearly with increasing x. With x increasing from 0 to 0.8, the dielectric constant decreases from 42 to 33, and Q×f value from 75,491 to 20,248 GHz. A nearly zero τ_f ceramic with dielectric constant of 33 and Q×f value of 20,248 GHz was obtained at x=0.8. The sintering temperature has slight effect on dielectric constant, but significant on Q×f value. The microstructures and crystal structures were characterized by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis techniques to reveal the mechanisms.     

Low loss and temperature stable microwave dielectric ceramics in (1 − x)Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>–xLi<Subscript>2</Subscript>Mg<Subscript>3</Subscript>TiO<Subscript>6</Subscript> (0.1 ≤ x ≤ 0.5) system

The (1???x)Li₂TiO₃–xLi₂Mg₃TiO₆ (x?=?0.1, 0.15, 0.2, 0.3, 0.4, 0.5) ceramics system was fabricated by solid-state synthesis. Test results of X-ray diffraction and electron diffraction spectrum show that all ceramic samples only contain Li₂TO₃ and Li₂Mg₃TiO₆ phase. Scanning electron microscope shows that pores were found in crystal grain due to Li volatilization in high temperature (>?1000 °C). With the rise proportion of Li₂Mg₃TiO₆ in ceramics, dielectric constant (?_r) decreases from 19.55 to 14.53, quality factor (Q×f) increases from 102,800 to 126,000 GHz and temperature coefficient (τ_f) decreases from +?15.9 to ??30.08 ppm/°C. High performance microwave dielectric properties of ?_r?=?18.5, Q×f?=?108,000 GHz, τ_f?=?4.2 ppm/°C were obtained at 1390 °C for 0.85Li₂TiO₃–0.15Li₂Mg₃TiO₆ ceramics. To suppress Li volatilization, LiF, a low temperature melting addition, was added to 0.85Li₂TiO₃–0.15Li₂Mg₃TiO₆ ceramics. LiF effective lowers sintering temperature from 1390 to 1175 °C due to LiF liquid-phase sintering and restricts Li evaporation, and a well-developed grain morphology and excellent dielectric properties (?_r?=?18.5, Q×f?=?87,000 GHz, τ_f?=???18 ppm/°C) was obtained which hold promise in 4G tele-communication applications.     

Microstructures and microwave dielectric properties of Li2ZnTi3O8 ceramics prepared by reaction-sintering process

The Li₂ZnTi₃O₈ ceramic was prepared by reaction-sintering process and its microwave dielectric properties were investigated. With increasing sintering temperature or dwell time, the relative densities, ε_r values and Q × f values of Li₂ZnTi₃O₈ ceramic increased initially and then decreased. The smaller τ_f value of Li₂ZnTi₃O₈ ceramic sintered at 975 °C was due to the low degree of oxygen octahedral distortion. When the sintering temperature exceeded 975 °C, the τ_f values of Li₂ZnTi₃O₈ ceramics were independent of sintering temperature. The tetragonal-shaped grains tend to appear in Li₂ZnTi₃O₈ ceramics sintered at higher temperature and longer dwell time, which was dominated by phase boundary reaction mechanism. Typically, The Li₂ZnTi₃O₈ ceramic sintered at 1,025 °C for 6 h had a maximum relative density of 97.4 % and good microwave dielectric properties of ε_r = 25.8, Q × f = 77,100 GHz, τ_f = ?12.4 ppm/°C. The results show that the reaction-sintering process is a simple and effective method to produce dense Li₂ZnTi₃O₈ ceramics with excellent dielectric properties.