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排序方式: 共有38条查询结果,搜索用时 16 毫秒
1.
M. Z. Harford Mark Rubinstein A. K. Singh A. E. Edelstein S. A. Wolf 《Journal of Superconductivity》1988,1(4):407-415
We have investigated the temperature dependence of the electrical transport and the thermogravimetric properties, from -200°C to +1000, of the Bi-Sr-Ca-Cu-O high-temperature superconductor. We conclude that this system has a cooperative, simultaneous-melting/oxygen desorption/metal-insulator transition that occurs near 900°C. We speculate on its nature and on its relationship to phenomena found in other high-T
c superconductors. 相似文献
2.
The influence of aluminum doping at Mn-site in nanograin compound La0.8Sr0.2MnO3 was investigated based on X-ray diffraction, scanning electron microscope and resistivity measurement, in the light of structure and transport properties. The results showed that Al doping was favorable to the globurizing of powders and grain size uniformity, however, depressed the particles growth. The resistivity of system increased rapidly and the metal-insulator transition temperature (TIM) and room temperature magnetoresistance decreased as the aluminum concentration increased. In the TTIM region, the current carriers were moving in variable range transition mode. The resistivity of La0.8Sr0.2Mn1-xAlxO3 for x=0.05 and 0.1 satisfied metal model in the TTIM region. The characteristics of the transport behavior for aluminum doping were analyzed in terms of destroying the double exchange channel of Mn3 -O-Mn4 , distortion of the cell lattice and change of powder particles size and shape. 相似文献
3.
Guangsheng Fu Xingkun Ning Mingjing Chen Shufang Wang Peng Liu Jianglong Wang Xiaowei Li 《Journal of the American Ceramic Society》2019,102(5):2761-2769
Recognizing and controlling the metal-insulator transition (MIT) in VO2 transition-metal oxides is interesting for the future electronic devices. However, the effect of the electron correlation for the structure-coupled MIT in VO2 is as yet an open question. In this study, we present for the first time direct spectroscopic evidence for the charge-transfer assistance bandwidth controlled MIT (BC-MIT) in Au–VO2 nanocomposite thin films (NCTFs). A significantly enhancement of the MIT temperature (about 350 K) is realized in Au–VO2 films with Au volume ratio of 1.1 mol%. However, by further increasing Au ratios, the MIT temperature in Au–VO2 NCTFs is downward shifted by ~16 K and forward shifted 6 K. The V L-edge and O K-edge have been investigated. The basic electronic parameters such as the covalency (W) have been tuned. The relationship between bandwidth and the MIT temperature has been clearly elucidated a linear relationship. The experimental results demonstrate that MIT in VO2 is BC-MIT which improved our understanding of the electron correlation effect in VO2 systems. 相似文献
4.
认真研究了 2维双交换模型的局域化性质 ,利用有限尺寸标度方法和转移矩阵技术计算了系统的局域化长度和电导。发现 ,在标度变换下 ,E 相似文献
5.
采用分子束外延(MBE)技术在单晶蓝宝石衬底上生长了高质量化学计量比二氧化钒(VO2)薄膜, 通过该技术实现薄膜厚度15~60 nm精确控制。对于优化条件下VO2薄膜, 实现了电阻率变化超过4个数量级的优异金属-绝缘体相变, 近似于之前报道高质量单晶VO2相变特性。特别是通过太赫兹时域光谱分析了不同厚度的VO2薄膜在太赫兹波段的光学特性。结果表明: VO2薄膜的厚度对其在太赫兹波段的光学特性有很大影响。因此, 为了获得更优的可靠性和重复性能, VO2薄膜的厚度必须得到精确控制。本研究结果对于下一步VO2基太赫兹器件研究具有重要意义。 相似文献
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A comparative study for two different series,La0.67Ca0.33Mn1-xCrxO3 and La0.67+xCa0.33-xMn1-x CrxO3,is performed with x changing from 0.04 to 0.08 through measurements of zero-field resistivity (ρ) magnetoresistance(MR) and ac susceptibility (x) as functions of temperature(T). For the second group,a single insulator-metal transition was characterized by the resistivity maximum appears in ρ VS.T curve.For the first group,besides the resistivity peak appearing at higher temperatures,the sample shows evidence for the existence of another peak appearing at lower temperatures.Compared to the first group,the second group shows a significant enhancement in MR effect,while the measurement of x-T dependence does not display obvious differences for the two series.Different behaviors observed in the tWO series are discussed by considering possible exchange interaction between Mn3+ ion and Cr3+ ion. 相似文献
9.
Nanocomposites containing Fe or FeCo (Fe-rich) dispersed in hexaferrites (M, W, or Y phase) are realized by the heterogeneous
solid-gas reduction under H2 + N2. Transmission electron microscopy (TEM) studies show that metal nanoparticles precipitate coherently as thin flakes along
the a-b planes of the hexaferrite lattice above the characteristic reduction temperature, TR >375°C. The electrical resistivity measurements reveal that the charge transport mechanism in the composites is by tunneling,
whereas samples having higher fractions of the alloy particles show metallic behavior. Controlled reduction at TR leads to apparent insulator-metal changeover in the ρ versus T plot. This changeover persists even in the presence of a high
magnetic field (7 T) and is ascribed to the percolation of metal particles caused by the difference in the coefficient of
thermal expansion between the constituents. In the insulator regime, negative magnetoresistance (MR) of ∼5–9% is observed
at 25°C. Further, ρ-T curves by the two-probe method exhibit hysteretic behavior caused by large inhomogeneity in the distribution
of metal content and the time-dependent charge accumulation (Coulomb blockade) at the metal granules for these composites.
They also exhibit nonlinearity in the current-voltage (I-V) characteristics with the nonlinearity coefficient ranging from
1.2 to 1.4 at different temperatures. 相似文献
10.
采用多步骤固态烧结方法合成了具有单一Co2P相的Co0.525Fe0.475MnP化合物,其反铁磁有序温度在室温附近。在升温过程中,这种化合物经历两个连续的磁转变:在285 K发生反铁磁到铁磁的一级相变,在375 K发生由铁磁到顺磁的二级相变。在0~5 T的外磁场中,两个相变点温度对应的最大磁熵变分别为1.1 J/(kg·K)(303 K)和-2.0 J/(kg·K)(383 K)。外磁场为零时,随着温度的降低电阻率曲线在铁磁到反铁磁转变温度附近出现极小值,是铁磁有序与反铁磁有序的竞争所致。在35 K再次出现的电阻率极小值,可归因于由Fe替代Co引起的自旋无序所导致的金属-绝缘体转变。在5 T磁场中磁电阻率的最大值对应温度为200 K时的-2.5%,在反铁磁温度以上磁电阻率迅速减小。这表明,这种化合物的磁电阻效应源于外磁场对反铁磁有序的影响。 相似文献