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1.
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
2.
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
3.
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
4.
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
5.
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
6.
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
7.
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.8.
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
9.
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
10.
MgO (0–2.0 vol%) added Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) ceramics have been prepared by the conventional solid-state reaction method. The effects of MgO powder on the phase formation, densification, dielectric, piezoelectric and mechanical properties (flexural strength, hardness) of the BZT-0.5BCT ceramics have been studied systematically. The synthesized powder could be densified to 97 % of true density at a temperature of 1350 °C. The MgO addition also provided materials with better mechanical properties. The most interesting aspect of MgO added samples is their relative permittivity vs. temperature response. MgO additions effectively suppress the relative permittivity around phase transition temperature. The aging rate of d33 observed for BZT-0.5BCT is 14 %/decade. MgO addition reduces the ageing rate and for 1 vol% MgO added, BZT-0.5BCT shows aging rate of 3 %/decade. BZT-0.5BCT/MgO ceramics possesses good mechanical properties viz., flexural strength 93 MPa, which is almost 25 % higher than that of monolithic BZT-0.5BCT (73 MPa). 相似文献
11.
N. J. Kidner Z. J. Homrighaus B. J. Ingram T. O. Mason E. J. Garboczi 《Journal of Electroceramics》2005,14(3):283-291
In the microcrystalline regime, the electrical (impedance/dielectric) behavior of grain boundary-controlled electroceramics is well described by the brick-layer model (BLM). In the nanocrystalline regime, however, grain boundary layers can represent a significant volume fraction of the overall microstructure. Simple boundary-layer models no longer adequately describe the electrical properties of nanocrystalline ceramics. The present work describes the development of a pixel-based finite-difference approach to treat a nested-cube model (NCM), which is used to investigate the validity of existing models for describing the electrical properties of polycrystalline ceramics over the entire range of grain core vs. grain boundary volume fractions, from the nanocrystalline regime to the microcrystalline regime. The NCM is shown to agree closely with the Maxwell-Wagner effective medium theory. 相似文献
12.
Perovskite-type Cd-doped LaCoO3 materials were synthesized by a simple solution-based combustion process. The synthesized materials were characterized by
powder X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance (DR) in the UV-VIS, and magnetic property
measurements. The parent LaCoO3 compound showed spin-glass transition at low temperatures, and with progressive Cd doping, showed transition to paramagnetic
ordering. The changes in magnetic properties of the materials are correlated to the changes in structural features resulting
from the Rietveld structural refinement of the materials. 相似文献
13.
C. M. Raghavan J. W. Kim S. S. Kim J. -W. Kim T. K. Song 《Journal of Electroceramics》2016,36(1-4):76-81
Aurivillius type five-layered V-doped Bi6Fe2(Ti3-xVx)O18+δ (x = 0.00, 0.03, 0.06, and 0.09) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. All the thin films were crystallized in Aurivillius structures, which have been confirmed by using X-ray diffraction and Raman spectroscopy studies. On comparing the thin films, the Bi6Fe2(Ti2.94V0.06)O18+δ thin film showed the most enhanced electrical and multiferroic properties, with a leakage current density value about four orders of magnitude lower than that of the Bi6Fe2Ti3O18 thin film, for example. All of these thin films showed anti-ferromagnetic hysteresis loops at room temperature. The significant decrease in the concentration of oxygen vacancies and the formation of a stable structure caused by doping with the donor V5+-ion are related to the improved properties in the V-doped Bi6Fe2(Ti3-xVx)O18+δ thin films. 相似文献
14.
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
15.
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
16.
A. V. Shlyakhtina S. N. Savvin A. V. Levchenko A. V. Knotko Petra Fedtke Andreas Busch Torsten Barfels Marion Wienecke L. G. Shcherbakova 《Journal of Electroceramics》2010,24(4):300-307
The electrical conductivity of new solid electrolytes Eu2.096Hf1.904O6.952 and Gd2Hf2O7 have been compared with those for different pyrochlores including titanates and zirconates Ln2+xМ2−xO7−δ (Ln = Sm-Lu; M = Ti, Zr; x = 0−0.81). Impedance spectroscopy data demonstrate that Eu2.096Hf1.904O6.952 and Gd2Hf2O7 synthesized from mechanically activated oxides have high ionic conductivity, comparable to that of their zirconate analogues.
The bulk and grain-boundary components of conductivity in Sm2.096Hf1.904O6.952 (Тsynth = 1600oС), Eu2.096Hf1.904O6.952 and Gd2Hf2O7 (Тsynth = 1670oС) have been determined. The highest bulk conductivity is offered by the disordered pyrochlores prepared at 1600oC
and 1670oC: ~1.5 × 10−4 S/cm for Sm2.096Hf1.904O6.952, 5 × 10−3 S/cm for Eu2.096Hf1.904O6.952 and 3 × 10−3 S/cm for Gd2Hf2O7 at 780oС, respectively. The conductivity of the fluorite-like phases at the phase boundaries of the Ln2+xМ2−xO7−δ (Ln = Eu, Gd; M = Zr, Hf; x ~ 0.286) solid solutions, as well as that of the high-temperature fluorite-like phases Ln2+xМ2−xO7−δ (Ln = Eu, Gd; M = Zr, Hf; x = 0−0.286), is lower than the conductivity of the disordered pyrochlores Ln2+xМ2−xO7−δ (Ln = Eu, Gd; M = Zr, Hf; x = 0−0.096). 相似文献
17.
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