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The spinel-type LiMn$_{2}$O$_{4}$ is a promising candidate as cathode material for rechargeable Li-ion batteries due to its good thermal stability and safety. Experimentally, it is observed that in this compound there occur the structural phase transitions from cubic ($Fd\bar{3}m)$ to tetragonal ($I4_{1}/{amd}$) phase at slightly below room temperature. To understand the phase transition mechanism, we compare the Gibbs free energy between cubic phase and tetragonal phase by including the configurational entropy. Our results show that the configurational entropy contributes substantially to the stability of the cubic phase at room temperature due to the disordered Mn$^{3+}$/Mn$^{4+}$ distribution as well as the orientation of the Jahn-Teller elongation of the Mn$^{3+}$O$_{6}$ octahedron in the the spinel phase. Meanwhile, the phase transition temperature is predicted to be 267.8 K, which is comparable to the experimentally observed temperature. These results serve as a good complement to the experimental study, and are beneficial to the improving of the electrochemical performance of LiMn$_{2}$O$_{4}$ cathode. 相似文献
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锗烷因其合适的带隙、较高的电子迁移速率、较好的环境稳定性、较小的电噪声和超薄的几何结构,有望取代现有硅基或锗基材料成为下一代半导体器件的理想载体.基于密度泛函理论和非平衡格林函数的第一性原理方法,研究了不同构型和浓度的氢空位簇对锗烷电子结构及锗烷中四硫富瓦烯(tetrathiafulvalene,TTF)分子掺杂性能的影响.计算结果表明,不同构型氢空位簇的引入可诱导Germanane Dehydrogenated-x H (GD–xH)体系产生不同性质的磁性,且磁矩大小亦与Lieb定理的预测结果相符,并能在GD-x H (x=1, 4, 6)体系自旋向下的能带结构中实现由缺陷态引起的类p型半导体掺杂效应,其电子激发所需的能量则会随着体系脱氢浓度的升高而不断降低.吸附TTF分子后, G/TTF和GD-xH/TTF (x=1, 2, 6)体系表现出分子掺杂效应,且GD-x H/TTF (x=1, 6)体系因分子轨道与缺陷态的杂化作用,可在自旋向上与自旋向下的能带结构中形成不同的掺杂类型.进一步的量子输运计算还表明, Armchair和Zigzag... 相似文献
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Phase-sensitive nonclassical properties of photon-added-then-subtracted coherent squeezed states 下载免费PDF全文
We investigate the nonclassical properties of the photon-added-then-subtracted coherent squeezed state(PASCSS) via the sub-Poissonian statistics,the photon-number distribution,and the negativity of the Wigner function.It is found that the PASSCS is a superposition state of D(β)S(ζ)|0>,D(β)S(ζ)|1>,and D(β)S(ζ)|2>.We find that the Mandel Q parameter,the photon-number distribution,and the negative volume of the Wigner function of the PASCSS are all periodic functions of the compound φ-θ/2 with a period π involved with squeezing and displacement parameters. 相似文献
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采用密度泛函理论框架下的第一性原理方法计算了ZnO/GaN核壳异质结的电子结构和光学特性.计算结果表明:[10 10]和[11 20]晶面的异质结在带隙边缘价带顶和导带底的电子态密度各自主要由氮原子和锌原子贡献.以[10 10]晶面为侧面的异质结结构的介电函数虚部(ε2)的曲线具有相似的特征,都是价带的氮原子到导带锌原子的跃迁,但峰位依赖于核层数和壳层数的不同而有所偏移.相对地,以[11 20]晶面为侧面的结构,其ε2的曲线与[10 10]晶面的情况有着很大的差别,其出现了一个由镓原子与氮原子之间的跃迁形成的峰.因此,可以通过控制异质结的晶面来实现对其光学特性的调控.这种新型异质结将在发光器件、光电太阳能电池、生物探测等方面具有一定的应用价值. 相似文献
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采用基于密度泛函理论的第一性原理方法研究了β-碳化硅/(15, 0) 碳纳米管和β-碳化硅/(16, 0)碳纳米管核壳结构的电子结构特性. 结果表明, 两种核壳异质结构都呈现出金属性, 它们的金属性主要是由碳纳米管和碳化硅纳米线表面的原子所贡献的. 碳化硅纳米线表面呈现的金属性由其结构本身决定, 而对于金属性的 (15, 0) 和半导体性的 (16, 0) 碳纳米管在填充碳化硅纳米线之后都表现出金属性, 主要是由于碳纳米管和碳化硅纳米线之间的电荷转移导致的, 而并不是由于碳纳米管形变造成的.
关键词:
核壳结构
电子结构
第一性原理 相似文献
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