共查询到17条相似文献,搜索用时 15 毫秒
1.
N. J. Kidner Z. J. Homrighaus B. J. Ingram T. O. Mason E. J. Garboczi 《Journal of Electroceramics》2005,14(3):293-301
The reduction of grain size from the microcrystalline regime into the nanocrystalline regime is known to produce significant changes in the transport properties of polycrystalline ceramics. Part 1 of this series [1] described the development of a pixel-based finite-difference nested-cube model (NCM), which was used to evaluate existing composite models for the electrical/dielectric properties of polycrystalline ceramics over the entire range of grain core vs. grain boundary volume fractions, from the nanocrystalline regime to the microcrystalline regime. Part 2 addresses grain shape and periodicity effects in such composite modeling, and the extraction of local materials properties (conductivity, dielectric constant) from experimental impedance/dielectric spectroscopy data. 相似文献
2.
The electric mechanisms of perovskite-type LaMnO3 was investigated with B-site substitution in this paper. Samples of La(TixMn1 − x)O3 (0.1 ≰ x ≰ 0.7) were sintered at different temperature. The voltage-temperature (V-T) curves of the samples were tested from room
temperature (25∘C) to 300∘C, then the electric properties were measured and analyzed. The experimental results showed that the resistivity-temperature
(ρ-T) curves of the samples matched NTC characteristic. The resistivity increased slightly with the increase of Ti amount as x was less than 0.5, however, it rose greatly after x exceeded 0.5; The sintering temperatures have a little influence on the resistivity, except for the sample with x = 0.7. 相似文献
3.
Strontium-doped lanthanum ferrites (LSF) were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), 4-point D.C. electrical conductivity and bulk property measurements. The results were compared to those of previous studies as well as selected processing conditions. The investigation focused on effects of sintering temperature, time, atmosphere (air, O2 and N2) and composition of La1–xSrxFeO3– (x = 0.2–0.9), on the sintering behavior, microstructural development and electrical conductivity. An oxalate precipitation method was used to prepare lanthanum ferrite powders. Simultaneous thermogravimetric and differential thermal analysis (TGA/DTA) studies found calcination temperatures of 800 and 850^C were necessary to form single-phase crystalline powders, as determined by XRD. Specimens were sintered from 1300 to 1400^C with dwell times from
to 2 hrs. Results from SEM/EDS analysis showed the presence of a second phase in the samples fired in air or oxygen. The second phase was not detected by x-ray diffraction due to the small amount of material present. Samples fired in nitrogen had the lowest conductivity while those fired in oxygen had the highest. A composition of x = 0.5 resulted in the highest conductivity, 352 S/cm, at an operating temperature of 550C in air. High strontium additions (x = 0.9) lowered the linear shrinkage of LSF. 相似文献
4.
The effect of mechanical loading on the tuning performance of a tunable Thin Film Bulk Acoustic Wave Resonator (TFBAR) based
on a Ba0.3Sr0.7TiO3 (BST) thin film has been investigated experimentally and theoretically. A membrane-type TFBAR was fabricated by means of
micromachining. The mechanical load on the device was increased stepwise by evaporating SiO2 on the backside of the membrane. The device was electrically characterized after each evaporation step and the results were
compared to those obtained from modeling. The device with the smallest mechanical load exhibited a tuning of − 2.4% and − 0.6%
for the resonance and antiresonance frequencies at a dc electric field of 615 kV/cm, respectively. With increasing mechanical
load a decrease in the tuning performance was observed. This decrease was rather weak if the thickness of the mechanical load
was smaller or comparable to the thickness of the active BST film. If the thickness of the mechanical load was larger than
the thickness of the active BST layer, a significant reduction in the tuning performance was observed. The weaker tuning of
the antiresonance frequency was due to a reduced tuning of the sound velocity of the BST layer with increasing dc bias. The
resonance frequency showed a reduced tuning due to a decrease in the effective electromechanical coupling factor of the device
with increasing mechanical load. With the help of the modeling we could de-embed the intrinsic tuning performance of a single,
non-loaded BST thin film. We show that the tuning performance of the device with the smallest mechanical load we fabricated
is close to the intrinsic tuning characteristics of the BST layer. 相似文献
5.
Bouhafs Khalfallah Fatima-Zohra Driss-Khodja Fatiha Saadaoui Mohammed Driss-Khodja Abdelkader Boudali Hanifi Bendaoud Bachir Bouhafs 《Journal of Computational Electronics》2018,17(4):1478-1491
The structural, elastic, electronic, vibrational, and optical properties of BaSe1?xTex alloys are investigated by means of the full-potential linearized augmented plane wave method. The exchange–correlation effects are treated with the local density approximation, as well as the GGA-PBE, GGA-PBEsol, and GGA?+?mBJ schemes of the generalized gradient approximation. Ternary BaSe1?xTex compounds have not yet been synthesized. Improved predictions of the structural parameters are obtained using the GGA-PBEsol approach. Calculations of the electronic and optical properties with the GGA?+?mBJ approach yield accurate results. Ternary BaSe1?xTex alloys are wide-band-gap semiconductors with a direct gap Γ–Γ. The upper valence band is mainly due to Se p and Te p states, while the bottom of the conduction band results essentially from Ba d states. The dielectric function, refractive index, reflectivity, absorption coefficient, and energy-loss function are calculated in the range 0–35 eV. The increase in x gives rise to a redshift of the optical spectra. BaSe1?xTex alloys exhibit reflective properties of metals in some energy ranges. The static dielectric constant ?1(0) and the static refractive index n0 are calculated. The investigation of the elastic and vibrational properties shows that ternary BaSe1?xTex should be mechanically and dynamically stable, elastically anisotropic, brittle, and relatively soft. 相似文献
6.
Partial electronic conductivity and chemical diffusivity of Li have been measured on the system of Li3xLa2/3–xTiO3 (LLT) with x = 0.13, a prospective Li+ electrolyte, against oxygen activity in the range of 10–22 < aO2 < 0.21 at 557, 610 and 663C, respectively by an ion-blocking polarization technique. It is found that the electronic conductivity of LLT, which in air is essentially an ionic conductor, varies as aO2–1/4 to render it mixed-conductive in reducing atmospheres, say, in aO2 < 10–12. The chemical diffusivity of component Li also increases from a value of the order of 10–8 cm2/s in air atmosphere up to a maximum on the order of 10–3 cm2/s as the electronic conductivity increases with decreasing oxygen activity. This is attributed to the variation of the electronic transference number and the thermodynamic factor with oxygen activity. The latter has been evaluated to be on the order of 10–103. 相似文献
7.
Alena Movchikova Olga Malyshkina Gunnar Suchaneck Gerald Gerlach Ralf Steinhausen Hans Theo Langhammer Christoph Pientschke Horst Beige 《Journal of Electroceramics》2008,20(1):43-46
In this work, the thermal square wave method at single-frequency (TSWM) was applied to functionally graded BaTi1−x
Sn
x
O3 samples with a tin gradient of 0.075 ≤ x ≤ 0.15. The samples were fabricated by sintering of bi-, tri- and tetramorph green bodies. The polarization at the back side
with a higher tin content was in opposite direction to the polarization of the surface with a lower tin content. This was
attributed to the appearance of a space charge layer. The determined depth profiles of the pyroelectric coefficient illustrate
the appearance of a nearly constant polarization in the region of lower tin concentration of tri- and tetramorph samples.
The pyroelectric coefficient profiles were in good agreement with the averaged over sample thickness pyroelectric coefficient
obtained separately by the quasistatic method. 相似文献
8.
Jolanda M. Spijkerman Esben T. Petersen Jeroen Hendrikse Peter Luijten Jaco J. M. Zwanenburg 《Magma (New York, N.Y.)》2018,31(3):415-424
Object
Cerebrospinal fluid (CSF) T 2 mapping can potentially be used to investigate CSF composition. A previously proposed CSF T 2–mapping method reported a T 2 difference between peripheral and ventricular CSF, and suggested that this reflected different CSF compositions. We studied the performance of this method at 7 T and evaluated the influence of partial volume and B 1 and B 0 inhomogeneity.Materials and methods
T 2-preparation-based CSF T 2-mapping was performed in seven healthy volunteers at 7 and 3 T, and was compared with a single echo spin-echo sequence with various echo times. The influence of partial volume was assessed by our analyzing the longest echo times only. B 1 and B 0 maps were acquired. B 1 and B 0 dependency of the sequences was tested with a phantom.Results
T 2,CSF was shorter at 7 T compared with 3 T. At 3 T, but not at 7 T, peripheral T 2,CSF was significantly shorter than ventricular T 2,CSF. Partial volume contributed to this T 2 difference, but could not fully explain it. B 1 and B 0 inhomogeneity had only a very limited effect. T 2,CSF did not depend on the voxel size, probably because of the used method to select of the regions of interest.Conclusion
CSF T 2 mapping is feasible at 7 T. The shorter peripheral T 2,CSF is likely a combined effect of partial volume and CSF composition.9.
Zixing Wang Changlai Yuan Qingning Li Qin Feng Fei Liu Yun Yang Changrong Zhou Guohua Chen 《Journal of Electroceramics》2018,40(2):99-106
A series of microwave dielectric ceramics of (1-x) BiVO4 -xLn2/3MoO4 (Ln = Er, Sm, Nd and La; x = 0.06, 0.08, 0.10) sintered below 900 °C were prepared via solid-state reaction. As the x values increase, the monoclinic scheelite continuously changes to a tetragonal structure at x = 0.10. The incorporation of Ln2/3MoO4 into the BiVO4 matrix increases the product (Q × f) of quality factor (Q) and resonance frequency (f), and temperature coefficient (τ f ), but lowers the dielectric constant (ε r). Microwave dielectric ceramics with low sintering temperatures (<900 °C) are obtained: ε r of ~71.1, 81.6, 75.6 and ~75.3; Q × f values of ~8292, 5508, 8695 and 9043 GHz; τ f of ~ ?51, 134, 149 and 158 ppm/°C, for 0.94BiVO4–0.06Er2/3MoO4, 0.92BiVO4–0.08Sm2/3MoO4, 0.9BiVO4–0.1Nd2/3MoO4 and 0.9BiVO4–0.1La2/3MoO4 ceramics, respectively. Moreover, (1-x) BiVO4 -xLn2/3MoO4 (Ln = Er, Sm, Nd and La; x = 0.06, 0.08 and 0.10) ceramics are chemically compatible with both Ag and Cu powders at their sintering temperatures. The series of microwave dielectric ceramics might be potential candidates for low temperature co-fired ceramics (LTCC) technology applications. 相似文献
10.
The article deals with construction of a simplified model of inhibition of nitric oxides formed in the combustors of the gas-turbine plants (GTPs) operating on natural gas. A combustor in which premixed, lean air–fuel mixtures are burnt is studied theoretically and experimentally. The research was carried out using a full-scale combustor that had parameters characteristic of modern GTPs. The article presents the results computed by the FlowVision software and the results of the experiments carried out on the test bench of the All-Russia Thermal Engineering Institute. The calculations and the tests were conducted under the following conditions: a flow rate of approximately 4.6 kg/s, a pressure to 450 kPa, an air temperature at the combustor inlet of approximately 400°C, the outlet temperature t3 ≤ 1200°C, and natural gas as the fuel. The comparison of the simulated parameters with the experimental results underlies the constructed correlation dependence of the experimental NOx emission on the calculated parameter of nonuniform fuel concentration at the premixing zone outlet. The postulate about a weak dependence of the emission of NOx formed upon combustion of a perfectly mixed air–fuel mixture—when the methane concentration in air is constant at any point of the air–fuel mixture, i.e., constant in the mixture bulk—on the pressure in the combustor has been experimentally proven. The correctness and the practicability of the stationary mathematical model of the mixing process used to assess the NOx emission by the calculated amount of the air–fuel mixture generated in the premixing zone has been validated. This eliminates some difficulties that arise in the course of calculation of combustion and formation of NOx. 相似文献
11.
Objective The objective of this study was to compare two different schemes for long-T
2 component suppression in ultrashort echo-time (UTE) imaging. The aim was to increase conspicuity of short-T
2 components accessible by the UTE technique.
Materials and methods A “dual-echo” and a magnetization-preparation approach for long-T
2 and fat suppression were implemented on clinical scanners. Both techniques were compared in 3D UTE exams on healthy volunteers
regarding short-T
2 Signal-to-noise ratio (SNR), long-T
2 suppression quality, and scan efficiency. A quantitative SNR evaluation was performed using ankle scans of six volunteers.
T
2 suppression profiles were simulated for both approaches to facilitate interpretation of the observations.
Results At 1.5 T, both techniques perform equally well in suppressing long-T
2 components and fat. Magnetization preparation requires more shimming effort due to the use of narrow-band pulses, while the
“dual-echo” technique requires a post-processing step to form a subtraction image. For scans with a short repetition time
(TR), the “dual-echo” approach is much faster than the magnetization preparation, which depends on slow T
1 recovery between preparation steps. The SNR comparison shows slightly higher short-T
2 SNR for the “dual-echo” approach. At 3.0 T, magnetization preparation becomes more challenging due to stronger off-resonance
effects.
Conclusion Both techniques are well suited for long-T
2 suppression and offer comparable short-T
2 SNR. However, the “dual-echo” approach has strong advantages in terms of scan efficiency and off-resonance behavior. 相似文献
12.
J. E. Fonseca S. Mishra S. Kaya R. F. Rakowski 《Journal of Computational Electronics》2008,7(1):20-23
Biologically-inspired nanodevices can serve as “natural” alternatives to conventional semiconductor devices in many applications
from information storage to mechanical rotors. In this work we consider an ATP-powered transmembrane protein, the Na+,K+-ATPase, which has appealing functionality but still lacks an “atomistic” picture capable of elucidating its operation. The
vast collection of experimental literature on the Na+,K+-ATPase gives a unique advantage to this protein in developing and validating computational tools. We have performed extensive
molecular dynamic simulations of the Na+,K+-ATPase in an accurate biological environment, followed by time-averaged electrostatic analysis, to investigate the ion-binding
loci and access/egress pathways that cations may take through the protein as they are transported across the membrane. 相似文献
13.
It is expected that published results from drift diffusion simulation of oxide thickness fluctuations in nano-scale devices
underestimates the true intrinsic device parameter variation by neglecting local variations in surface roughness scattering.
We present initial results from 3D ‘bulk’ Monte Carlo simulation including an ab initio treatment of surface roughness scattering capable of capturing such transport variation. The scattering is included directly
through the real space propagation of carriers in the fluctuating potential associated with a randomly generated interface.
We apply this approach to simulate inversion layer mobility in order to validate the model before its possible application
in device variability simulations. Qualitative agreement is found with universal mobility data and avenues for possible calibration
of surface and simulation parameters are highlighted. 相似文献
14.
Trang An Duong Hyoung-Su Han Young-Hwan Hong Young-Seok Park Hoang Thien Khoi Nguyen Thi Hinh Dinh Jae-Shin Lee 《Journal of Electroceramics》2018,41(1-4):73-79
This study investigated the microstructure, crystal structure, and electrical properties of (1???x)Bi1/2Na1/2TiO3–xSrTiO3 (BNST100x; x?=?0.20, 0.22, 0.24, 0.26, 0.28, and 0.30) lead?free piezoceramics. The average grain size of BNST100x ceramics decreased with increasing SrTiO3 content. A phase transition from nonergodic relaxor (NER) to ergodic relaxor (ER) was observed at x?=?0.26, and the highest unipolar strain under 4 kV/mm electric field, of 0.25% (d33*?≈?620 pm/V), was obtained at x?=?0.28. We found that the BNST26 and BNST28 compositions yielded the competitive advantage of larger strain values under lower operating fields compared with other BNT–based lead–free piezoelectric ceramics. Therefore, we regard these ceramics as promising candidates for actuator applications. 相似文献
15.
Chang-Heon Lee Hyoung-Su Han Seong Hyun Kim Thi Hinh Dinh Chang Won Ahn Jae-Shin Lee 《Journal of Electroceramics》2018,41(1-4):43-49
This study examined the microstructures, crystal structures, and electrical properties of 0.01 mol CuO–added (1–x)(Bi1/2Na1/2)TiO3–xSrTiO3–2BiFeO3 (BNST100x–2BF, x?=?0.20 ~ 0.28) ceramics synthesized at two different sintering temperatures. The sintering temperature of the BNST100x–2BF ceramics could be decreased from 1175 °C to 1000 °C by adding a 0.01 mol CuO excess. Low–temperature sintering led to a decrease in average grain size. The dielectrics, polarization hysteresis (P–E), switching current, and electric–field induced strain (S–E) curves changed with increasing SrTiO3 content and decreasing sintering temperature. Interestingly, the highest reduction ratio of d33* was calculated to be somewhere in between the high–temperature sintered and low–temperature sintered BNST26–2BF ceramics. These results were attributed to the difference in the stabilized relaxor state and closely related to the electric field–induced reversible phase transition from the relaxor and ferroelectrics. 相似文献
16.
Chang Sub Kim Nicola H. Perry Sean R. Bishop Harry L. Tuller 《Journal of Electroceramics》2018,40(4):332-337
The thermal and chemical expansion of a potential solid oxide fuel cell (SOFC) cathode material SrSn0.65Fe0.35O3–0.35/2+δ (SSF35) were investigated to assess its thermo-chemo-mechanical stability at SOFC operating temperatures and to establish the correlation between defect concentrations (oxygen vacancies and electrons) and chemical expansion with the aid of the defect chemical model reported in part I of this study. Thermochemical expansion was measured as a function of temperature and oxygen partial pressure. The chemical expansion of SSF35 showed a strong correlation with changes in oxygen nonstoichiometry associated with changes in Fe valence state. Coefficients of both chemical (CCE) and thermal (CTE) expansion were calculated and found to be smaller than that of the closely related mixed conducting perovskite oxide SrTi0.65Fe0.35O3–0.35/2+δ (STF35). The thermal expansion coefficient of SSF was found to be close to that of YSZ (most popular solid oxide electrolyte), which makes SSF35 more attractive in terms of overall thermo-chemical stability. The chemical expansion of SSF35 showed decreasing CCE with increasing temperature and decreasing CTE with increasing oxygen deficiency, both opposite to the trends observed for STF35. Distortion in symmetry from the cubic structure seems to be responsible for the smaller coefficients and increasing asymmetry with expansion seems accountable for opposite trends of CCE and CTE compared to the STF counterpart. 相似文献
17.
The bulk electrical conductivity of the mixed ionic-electronic conducting perovskite-structured SrSn1-xFexO3-x/2+δ (SSF) was measured to examine how changes in defect chemistry and electronic band structure associated with the substitution of Ti by Sn impact defect charge carrier density and ultimately electrode performance. These results complement a defect chemical model for SSF investigated and reported in Part I of this study. The electrical properties of SSF were found not to differ significantly from the corresponding composition in SrTi1-xFexO3-x/2+δ (STF). It is believed that Fe dominates the character of the valence and conduction bands and thus governs the electronic properties in SSF. Though slightly shifted in energy due to the larger size of Sn, the defect equilibria and therefore the electrical conductivity of SSF were found to be largely dominated by Fe and thus differed only in a limited way from that in STF. Key kinetic parameters obtained include the migration enthalpy of oxygen vacancies (0.772 ± 0.204 eV), the activation energy of area-specific-resistance for oxygen exchange (1.65 ± 0.03 eV) and the magnitudes of electron (0.0002 ± 0.00005 cm2/V?s) and hole (0.0037 ± 0.0015 cm2/V?s) mobilities. 相似文献