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1.
Xuqiu Yang Pengcheng Zhai An Zhou Lisheng Liu Qingjie Zhang 《Journal of Electronic Materials》2009,38(7):1189-1193
For the binary thermoelectric material CoSb3 with a complex crystal structure, the Morse potential functional form is employed to describe its three-dimensional atomic
interactions. The mechanical responses and deformation behavior of a rectangular cross-section CoSb3 nanowire subjected to uniaxial tensile strain are simulated at constant temperature by the molecular dynamics method. The
deformation is strain controlled with constant strain rate. When the strain increases, necking gradually becomes distinct
near the middle of the model, and complete damage occurs at around 60% strain. The single-crystal CoSb3 nanowire exhibits properties distinct from those of single-crystal CoSb3 bulk previously studied. Comparison of the stress–strain curves and configuration evolutions of the CoSb3 nanowire and bulk during tensile loading indicate that an interesting brittle–ductile transition phenomenon occurs when the
single-crystal CoSb3 varies from bulk to nanowire. Future efforts should be devoted to seeking the critical dimension at which this transition
happens and the mechanism behind it. 相似文献
2.
Jiong Yang L. Xi W. Zhang L. D. Chen Jihui Yang 《Journal of Electronic Materials》2009,38(7):1397-1401
We present an investigation of electronic structures and electrical transport properties of some filled CoSb3 skutterudites by combining ab initio projected augmented plane-wave calculations and Boltzmann transport theory with electron group velocity evaluated by the
momentum matrix method. The systems are studied in a 2 × 2 × 2 supercell of Co4Sb12 to reveal the effects induced by different filler atoms and their filling fractions. The temperature dependences of the Seebeck
coefficient and power factor are studied, and they are in good agreement with experimental data. Our results reveal an optimal
filling fraction for n-type filled CoSb3 skutterudites and related compounds for achieving the highest power factor values. 相似文献
3.
Pengfei Wen Peng Li Qingjie Zhang Fajun Yi Lisheng Liu Pengcheng Zhai 《Journal of Electronic Materials》2009,38(7):1200-1205
The effect of cyclic thermal loading on the microstructure and thermoelectric properties of CoSb3 was investigated. The microstructures of the samples were characterized by x-ray diffractometry, scanning electron microscopy,
energy dispersive x-ray spectrometry and density measurements. The electrical conductivity, the Seebeck coefficient and the
thermal conductivity were measured from room temperature to 800 K. Under cyclic thermal loading, antimony partially volatilized
from the surface of the sample, and the density obviously decreased. After 2000 cycles, the phase composition of the sample
remained stable, and the average grain size did not change significantly. Moreover, the electrical conductivity varied only
slightly, except in the low temperature region. The Seebeck coefficient decreased slightly. However, the thermal conductivity
changed remarkably with increasing numbers of thermal cycles. 相似文献
4.
D. G. Ebling A. Jacquot H. Böttner L. Kirste J. Schmidt M. Aguirre 《Journal of Electronic Materials》2009,38(7):1450-1455
Thermoelectric compounds based on doped bismuth telluride and its alloys have recently attracted increasing interest. Due
to their structural features they show increased values of the thermoelectric figure of merit (ZT). A promising approach to improve the thermoelectric properties is to manufacture nanocomposite materials exhibiting lower
thermal conductivities and higher ZT. The ZT value of compounds can be shifted reasonably to higher values (>1) by alloying with IV-Te materials and adequate preparation
methods to form stable nanocomposites. The influence of PbTe and Sn on the thermoelectric properties is studied as a function
of concentration and preparation methods. Melt spinning and spark plasma sintering were applied to form nanocomposite materials
that were mechanically and thermodynamically stable for applications in thermoelectric devices. The structural properties
are discussed based on analysis by transmission electron microscopy and x-ray diffraction. 相似文献
5.
Ternary rare-earth sulfides NdGd1+x
S3, where 0 ≤ x ≤ 0.08, were prepared by sulfurizing Ln2O3 (Ln = Nd, Gd) with CS2 gas, followed by reaction sintering. The sintered samples have full density and homogeneous compositions. The Seebeck coefficient,
electrical resistivity, and thermal conductivity were measured over the temperature range of 300 K to 950 K. All the sintered
samples exhibit a negative Seebeck coefficient. The magnitude of the Seebeck coefficient and the electrical resistivity decrease
systematically with increasing Gd content. The thermal conductivity of all the sintered samples is less than 1.9 W K−1 m−1. The highest figure of merit ZT of 0.51 was found in NdGd1.02S3 at 950 K. 相似文献
6.
In this work, nano-structured Bi2Te3 and PbTe thermoelectric materials were synthesized separately via solvothermal, hydrothermal and low-temperature aqueous
chemical routes. X-ray diffraction (XRD), field-emission scanning-electron microscopy (FESEM), transmission electron microscopy
(TEM), and energy dispersive spectroscopy (EDS) were used to analyze the powder products. Results showed that the as-prepared
Bi2Te3 samples were all single-phased and consisted of irregular spherical granules with diameters of ∼30 nm whereas the PbTe samples
were mainly composed of well-crystallized cubic crystals with average size of approximately 100 nm. Some nanotubes and nanorods
were found in Bi2Te3 and PbTe samples, respectively; these were identified as Bi2Te3 nanotubes and PbTe nanorods by EDS analysis. Possible reaction mechanisms for these syntheses are discussed in detail herein. 相似文献
7.
Two 10-mm-long multilayer prototype actuators were fabricated by a stack method using 55 pieces of 5 mm×5 mm×0.15 mm Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMNT) single crystals and PZT-5A ceramics, respectively. The strain values for PMNT multilayer piezoelectric actuators are
twice those of PZT-5A multilayer actuators, and 20.8-μm displacements can be achieved at the same E-field of 15 kV/cm. Although
thermal and electrical history markedly impact dielectric and piezoelectric performance of PMNT crystals, the PMNT multilayer
actuator can still achieve large displacements with approximately linear behavior below 60°C. Broad stable dynamic displacement
characteristic and fast displacement response make the new-type actuators promising candidates for the application in new-generation
high-performance solid-state actuators. 相似文献
8.
Wein-Duo Yang Yen-Hwei Chang Chia-Chia Huang Yu-Chung Chen 《Journal of Electronic Materials》2009,38(3):460-467
Highly sensitive CO gas sensors based on heterocontacts of ZnO:Al on La0.8Sr0.2Co0.5Ni0.5O3 (LSCNO) were fabricated successfully. La0.8Sr0.2Co0.5Ni0.5O3 thin films were coated on (100) silicon wafers by a sol-gel method including the Pechini process followed by a spin-coating
procedure. Then, ZnO:Al films prepared by radiofrequency (RF) magnetron sputtering at various oxygen partial pressures and
deposited on as-deposited La0.8Sr0.2Co0.5Ni0.5O3 films were investigated. The results revealed that the CO sensing ability of the film prepared with the ratio of O2/Ar = 5/5 (ratio of volume flow rate) was the worst, owing to the highest (002) plane orientation in the ZnO:Al film. In contrast,
the ZnO:Al film prepared with O2/Ar = 3/7 exhibited better CO sensitivity. Furthermore, all two-layer samples showed higher CO sensitivities than single-layer
samples. The CO sensitivity of ZnO:Al/La0.8Sr0.2Co0.5Ni0.5O3 thin film was 45% for 500 ppm CO at a sensing temperature of 200°C. 相似文献
9.
Shih-Yuan Lin Ying-Chung Chen Chih-Ming Wang Kuo-Sheng Kao Chih-Yuan Chan 《Journal of Electronic Materials》2009,38(3):453-459
Calcium copper titanium oxide (CaCu3Ti4O12, abbreviated to CCTO) films were deposited on Pt/Ti/SiO2/Si substrates at room temperature (RT) by radiofrequency magnetron sputtering. As-deposited CCTO films were treated by rapid
thermal annealing (RTA) at various temperatures and in various atmospheres. X-ray diffraction patterns and scanning electron
microscope (SEM) images demonstrated that the crystalline structures and surface morphologies of CCTO thin films were sensitive
to the annealing temperature and ambient atmosphere. Polycrystalline CCTO films could be obtained when the annealing temperature
was 700°C in air, and the grain size increased signifi- cantly with annealing in O2. The 0.8-μm CCTO thin film that was deposited at RT for 2 h and then annealed at 700°C in O2 exhibited a high dielectric constant (ε′) of 410, a dielectric loss (tan δ) of 0.17 (at 10 kHz), and a leakage current density (J) of 1.28 × 10−5 A/cm2 (at 25 kV/cm). 相似文献
10.
We discuss the thermoelectric properties of Na
x
CoO2 using the electronic structure, as determined in first principles calculations, and Boltzmann kinetic transport theory. The
Fermi energy lies near the top of a manifold of Co t
2g
bands. These t
2g
bands are separated by a large gap from the higher-lying e
g
states. Although the large crystal-field splitting implies substantial Co–O hybridization, the bands are narrow. Application
of standard Boltzmann transport theory to such a narrow band structure yields high thermopowers in accord with experimental
observations, even for high metallic carrier densities. The high thermopowers observed for Na
x
CoO2 can therefore be explained by standard band theory and do not rely on low dimensionality or correlation effects specific
to Co. We also present results for the cubic spinel structure ZnRh2O4. Like Na
x
CoO2, this compound has very narrow valence bands. We find that if it could be doped with mobile carriers, it would also have
a high thermopower, comparable with that of Na
x
CoO2. 相似文献
11.
C. X. Wang N. Maeda M. Hiroki T. Tawara T. Makimoto T. Kobayahsi T. Enoki 《Journal of Electronic Materials》2005,34(4):361-364
AlGaN/GaN-based metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) with Al2O3/Si3N4 bilayer as insulator have been investigated in detail, and compared with the conventional HFET and Si3N4-based MIS-HFET devices. Al2O3/Si3N4 bilayer-based MIS-HFETs exhibited much lower gate current leakage than conventional HFET and Si3N4-based MIS devices under reverse gate bias, and leakage as low as 1×10−11 A/mm at −15 V has been achieved in Al2O3/Si3N4-based MIS devices. By using ultrathin Al2O3/Si3N4 bilayer, very high maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been obtained in the MIS-HFET
device with gate length of 1.5 μm, a reduction less than 5% in maximum transconductance compared with the conventional HFET
device. This value was much smaller than the more than 30% reduction in the Si3N4-based MIS device, due to the employment of ultra-thin bilayer with large dielectric constant and the large conduction band
offset between Al2O3 and nitrides. This work demonstrates that Al2O3/Si3N4 bilayer insulator is a superior candidate for nitrides-based MIS-HFET devices. 相似文献
12.
Shi-Jin Ding Min Zhang Wei Chen David Wei Zhang Li-Kang Wang 《Journal of Electronic Materials》2007,36(3):253-257
Metal-insulator-silicon capacitors have been fabricated using novel insulators of SiO2/HfO2-Al2O3-HfO2 (HAH)/Al2O3 and metallic HfN gate, exhibiting a program-erasable characteristic. The memory capacitor presents a large memory window
of 2.4 V under +12 V program/–14 V erase for 10 ms, no erase saturation, and sufficient electron- and hole-trapping efficiencies
such as an electron density of ∼7 × 1012 cm–2 under 13 V program for 0.5 ms and a hole density of ∼4 × 1012 cm–2 under –12 V erase for 0.5 ms. The observed properties are attributed to the introduction of high permittivity atomic-layer-deposited
HAH/Al2O3 as well as high work function HfN gate. The related mechanism is addressed accordingly. 相似文献
13.
The effect of nano Cr2O3 additions in (Bi, Pb)-Sr-Ca-Cu-O superconductors using the coprecipitation method is reported. Nano Cr2O3 with 0.1, 0.3, 0.5, 0.7, and 1.0 wt.% were added to the (Bi, Pb)-Sr-Ca-Cu-O system. The critical temperature (T
c) and transport critical current density (J
c) were determined by the four-point probe technique. The phases in the samples were determined using the powder X-ray diffraction
method. The microstructure was observed by a scanning electron microscope and the distribution of nano Cr2O3 was determined by energy-dispersive X-ray analysis (EDX). The maximum T
c and J
c were observed for the sample with 0.1 wt.% nano Cr2O3. The variation in the J
c of all the samples was explained by the effective flux pinning by nano Cr2O3 in the samples. Using the self-field approximation together with the dependence of J
c on temperature, the characteristic length (L
c) associated with the pinning force was estimated to be approximately the same as the average grain size in all the samples. 相似文献
14.
A.E. Bekheet 《Journal of Electronic Materials》2008,37(4):540-544
Ga2Se3 films were deposited by the thermal evaporation of the bulk material onto pyrographite substrates under vacuum. The I–V characteristic curves were found to be typical for a memory switch. They exhibited a transition from an ohmic region in the
lower-field region to a non-ohmic region in the high-field region in the preswitching region, which has been explained by
the Poole–Frenkel effect. The temperature dependence of the resistance in the ohmic region was found to be that of a thermally
activated process. It was also found that the mean value of the switching voltage increased linearly with increasing film
thickness in the range from 291 nm to 516 nm, while it decreased exponentially with increasing temperature in the range from
298 K to 393 K. The results were explained in accordance with the electrothermal model for the switching process. 相似文献
15.
P.N. Alboni X. Ji J. He N. Gothard J. Hubbard Terry M. Tritt 《Journal of Electronic Materials》2007,36(7):711-715
Because of their good electrical transport properties, skutterudites have been widely studied as potential next-generation
thermoelectric (TE) materials. One of the main obstacles to further improving their thermoelectric performance has been reducing
their relatively high thermal conductivity. To some extent, this hindrance has been partially resolved by filling the voids
found in the skutterudite structure with so-called “rattling” atoms. It has been predicted that reducing the dimensionality
in a TE material would have a positive effect in enhancing its thermoelectric properties, for example increasing the thermopower
and reducing the thermal conductivity. Introducing nanoparticles into the skutterudite materials could therefore have favorable
effects on their electrical properties and should also reduce lattice thermal conductivity by introducing extra scattering
centers throughout the sample. Nanoparticles may also be used in conjunction with void filling for further reduction of the
thermal conductivity of skutterudites. Cobalt triantimonide (CoSb3) samples with different amounts of embedded nanoparticles have been grown, and the electrical and thermal transport properties
for these composites have been measured from 10 K to 650 K. The synthetic techniques and electrical and thermal transport
data are discussed in this paper. 相似文献
16.
Ca
z
Co4−x
(Fe/Mn)
x
Sb12 skutterudites were prepared by mechanical alloying and hot pressing. The phases of mechanically alloyed powders were identified
as γ-CoSb2 and Sb, but they were transformed to δ-CoSb3 by annealing at 873 K for 100 h. All specimens had a positive Hall coefficient and Seebeck coefficient, indicating p-type conduction by holes as majority carriers. For the binary CoSb3, the electrical conductivity behaved like a nondegenerate semiconductor, but Ca-filled and Fe/Mn-doped CoSb3 showed a temperature dependence of a degenerate semiconductor. While the Seebeck coefficient of intrinsic CoSb3 increased with temperature and reached a maximum at 623 K, the Seebeck coefficient increased with increasing temperature
for the Ca-filled and Fe/Mn-doped specimens. Relatively low thermal conductivity was obtained because fine particles prepared
by mechanical alloying lead to phonon scattering. The thermal conductivity was reduced by Ca filling and Fe/Mn doping. The
electronic thermal conductivity was increased by Fe/Mn doping, but the lattice thermal conductivity was decreased by Ca filling.
Reasonable thermoelectric figure-of-merit values were obtained for Ca-filled Co-rich p-type skutterudites. 相似文献
17.
Mg2Sn compounds were prepared by the modified vertical Bridgman method, and were doped with Bi and Ag to obtain n- and p-type materials, respectively. Excess Mg was also added to some of the ingots to compensate for the loss of Mg during the
preparation process. The Mg2Sn samples were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM), and their power factors were
calculated from the Seebeck coefficient and electrical conductivity, measured from 80 K to 700 K. The sample prepared with
4% excess Mg, which contains a small amount of Mg2Sn + Mg eutectic phase, had the highest power factor of 12 × 10−3 W m−1 K−2 at 115 K, while the sample doped with 2% Ag, in which a small amount of eutectics also exists, has a power factor of 4 × 10−3 W m−1 K−2 at 420 K. 相似文献
18.
Single phase β-Zn4Sb3 was prepared by the application of a two-stage heat treatment, and impurity elements were doped. The undoped and doped samples
were prepared by direct melting followed by two-stage heat treatment at 450°C and 400°C after solidification of the samples
in sealed quartz ampoules. Impurity doping of the samples was performed by the addition of 1 at.% of Se, In, Pb, Te, or Bi.
The resulting samples were characterized by x-ray diffraction (XRD), differential thermal analysis (DTA), optical microscopy,
and electron probe microanalysis, and their Seebeck coefficients were determined at room temperature. The undoped samples
were determined by XRD and DTA to comprise single phase β-Zn4Sb3, while the doped samples were composed of multiple phases. From the measurements of the Seebeck coefficient, all samples
were found to be p-type and all were found to have almost the same values. These results indicate that β-Zn4Sb3 has limited solubility for these impurity elements. 相似文献
19.
Huanfu Zhou Hong Wang Kecheng Li Haibo Yang Minghui Zhang Xi Yao 《Journal of Electronic Materials》2009,38(5):711-716
The influence of BaCu(B2O5) (BCB) addition on the sintering temperature and microwave dielectric properties of ZnO-2TiO2-Nb2O5 (ZTN) ceramic has been investigated using dilatometry, x-ray diffraction, scanning electron microscopy, and microwave dielectric
measurements. A small amount of BCB addition to ZTN can lower the sintering temperature from 1100°C to 900°C. The reduced
sintering temperature was attributed to the formation of the BCB liquid phase. The ZTN ceramics containing 3.0 wt.% BCB sintered
at 900°C for 2 h have good microwave dielectric properties of Q × f = 19,002 GHz (at 6.48 GHz), ε
r = 45.8 and τ
f
= 23.2 ppm/°C, which suggests that the ceramics can be applied in multilayer microwave devices, provided that Ag compatibility
exists. 相似文献
20.
Thickening behavior of interfacial η (Cu6Sn5) phase and ɛ (Cu3Sn) phase intermetallic layers was investigated in liquid tin/solid copper reaction couples over reaction times from 30 sec
to over 4,000 min and temperatures from 250°C to 325°C. A scanning electron microscope (SEM) was used to quantify the interfacial
microstructure at each processing condition. The η developed with a scalloped morphology, while the ɛ always grew as a somewhat
undulated planar layer in phase with the η. The thickness of each phase was quantitatively evaluated from SEM micrographs
using imaging software. Thickening kinetics of the ɛ and η compounds were modeled using time- and temperature-dependent empirical
power-law equations. From the model, values for the kinetic exponent, rate constant, and activation energy were established
for each intermetallic layer. Measured values for the kinetic exponents and activation energies suggest that thickening of
the η is controlled by a grain-boundary diffusion mechanism, and growth of the ɛ occurs by solid-state diffusion, probably
grain-boundary diffusion. 相似文献