共查询到20条相似文献,搜索用时 156 毫秒
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本文采用脉冲激光沉积(PLD)方法,在NdGaO3(110)衬底上制备出了由钙钛矿锰氧化物材料La0.7Sr0.3MnO3和正铁氧体材料SmFeO3构成的高质量外延超晶格.在这一超晶格体系中,固定层数不变,当La0.7Sr0.3MnO3层厚度大于SmFeO3层的厚度时,超晶格的晶格逐渐发生弛豫,反之,则与衬底很好地共格.此外,伴随着这种应变状态的改变,超晶格的磁转变温度TC逐步增加,易磁化轴发生转变.我们认为这种应力状态以及磁性质的改变来源于强正交性的SmFeO3与菱形La0.7Sr0.3MnO3中氧八面体的界面耦合. 相似文献
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用等效介质理论计算了半无限侧向铁磁/铁磁超晶格的推迟模式.且以Co/Ni体系超晶格为例具体计算了该超晶格的表面模式和体模式,展示出一些与磁性/非磁性超晶格不同的有趣性质.侧向磁性/磁性超晶格具有较复杂的推迟模式,这是一种具有高度一般性的体系,在改变构成超晶格的两种铁磁层的厚度的比值、外场时,可以调节两支表面模式的频率以及体模式的频带,这种调节作用是与两种铁磁层的饱和磁化值有关的.当饱和磁化值相差较大时,调制效果是很明显的.当第二种铁磁介质饱和磁化值趋于零时,该体系演变成熟知的磁性/非磁性超晶格.当取麦克斯
关键词:
铁磁/铁磁超晶格
推迟模式
等效介质理论
自旋波谱 相似文献
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We systematically analyze the effects of the use of an inaccurate supercell termination and an insufficient supercell size of plane-wave expansion method on the dispersion and the slow light properties of the photonic crystal waveguides. The inattentive use of supercells of photonic crystal waveguides appeared in the literature is found to be yielding errors in the dispersion and slow light characteristics of the fundamental guided mode of photonic crystal waveguides. In addition, extra modes appear in the photonic band gap of the photonic crystal waveguide due to inaccurate supercell termination. By examining the field distribution of the modes, the extra modes can be determined and removed from the band diagram. The dispersion, group index and bandwidth characteristics are observed to be less affecting from inaccurate supercell termination as the number of rows adjacent to the waveguide increases. Moreover, the dispersion and the group index-frequency curves of the fundamental guided mode of correctly terminated supercells are found to be converging as the lateral row number along the line-defect is increased. 相似文献
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锆合金(如:锆铌(Zr-Nb)合金)的辐照损伤问题是裂变堆结构材料和燃料棒包壳材料设计的关键,而深入理解辐照损伤的物理机制,往往需借助于原子尺度的计算模拟,如:分子动力学和第一性原理等.针对随机置换固溶体合金的模拟,首先需构建能反映合金元素随机分布特征的大尺寸超胞,然而第一性原理计算量大,不宜使用过大(如≥200原子)超胞.通常第一性原理计算使用的是特殊准随机(SQS)超胞,SQS超胞可部分反映合金元素的随机分布特性,但对于特定组分只对应一种构型,这种模型是否能反映真实随机置换固溶体中多种局域构型的统计平均还有待进一步研究验证.分子动力学可在更大的尺度上进行计算模拟,能够通过随机取代(RSS)模型研究更多的合金构型,因此,本文基于RSS超胞模型及SQS扩展超胞模型,运用分子动力学方法对Zr-Nb合金进行了研究.首先通过构型误差分析确定了能真实反映固溶体合金性能统计性的RSS超胞的临界尺寸;然后计算比较了Zr-Nb合金SQS扩展超胞和一系列RSS超胞的晶格常数、形成能和能量—体积关系.研究表明,利用SQS超胞模拟得到的固溶体的晶格常数、形成能和能量体积曲线与一系列RSS超胞的对应统计值接近,因而SQS超胞可用于研究随机置换固溶体合金. 相似文献
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Shigenori Matsushima Kenji Takehara Kenji Yamada Masao Arai 《Journal of Physics and Chemistry of Solids》2007,68(2):206-210
The electronic structure of S-doped TiO2 with an optimized anatase structure was calculated within the framework of the density functional theory (DFT). For the calculation we built four kinds of supercells; type-A and B supercells consist of 12 and 48 atoms and a centered Ti atom is substituted for an S atom, while type-C and D supercells consist of 12 and 48 atoms and a centered O atom is substituted for an S atom. The supercells (type-B and D) were employed to adjust the S-concentration in TiO2 to an experimental value of a few %. The changes of the lattice parameters are not significant in the type-A and B supercells. The phase transition from the tetragonal to the orthorhombic occurs in the type-C and D supercells. In the small supercell (type-A), S-related states are located in the range of −1.6 to 0 eV, and the S-states are band-like. In contrast, in the large supercell (type-B), S-related states appeared at about 0.9 eV above the top of the valence band, and the S-states are atomic-like. The localization of the S-related states is remarkable in the type-B supercell. In the type-D supercell, the S-related states were merged with the top of the valence band, and as a result the band-gap energy is narrowed by 0.7 eV. Despite a low S-concentration (3%) in the type-D supercell, the S-related states are somewhat band-like. 相似文献
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The results of first-principles crystal structure optimization for the bulk rutile-type tin dioxide and its (110) and (001) surfaces as obtained by applying the siesta code, that incorporates norm-conserving pseudopotentials and strictly localized basis of pseudoatomic orbitals, are summarized. The relaxation near the (110) surface has been studied with the use of small supercells Sn 6 O 10 and Sn 6 O 12 , representing reduced and stoichiometric compositions, respectively,and compared with previously known results of other simulations. Further on, the effect of relaxation has been studied for a larger (stoichiometric) supercell Sn 10 O 20 . While qualitatively the same as obtained for small supercells, the relaxation pattern shows however numerical differences. The relaxation study at the (001) surface shows, as the major effect, the inward relaxation of the upper tin layer and the outward displacement of upper oxygen atoms (by , 0.3 Å) with respect to it. When going deep into the crystal, the values of Sn-Sn interplane distances and O-Sn interplane displacements fluctuate around the corresponding values in the bulk and decrease. They are not yet stabilized near the 5th tin layer from the surface, implying the need to consider even larger supercells for the accurate numerical estimations of the relaxation at the surface. 相似文献
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Charles W. Myles Byeong C. HaYoung K. Park 《Journal of Physics and Chemistry of Solids》2002,63(9):1691-1698
We have performed molecular dynamics simulations of the defect formation associated with the Staebler-Wronski (SW) effect in a-Si:H using 224 and 231 atom supercells and employing semiempirical Si-Si and Si-H total energy functionals. The role of hydrogen in the defect formation within the bond breaking model of the SW effect has been investigated for both large supercells. The results suggest that, within this model, H can be important in weakening the normal Si-Si bonds which break to produce defects in the SW effect. 相似文献
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A theoretical prediction of ion conductivity for solid state HfO2 is carried out in analogy to ZrO2 based on the density functional calculation. Geometric and electronic structures of pure bulks exhibit similarity for the two materials. Negative formation enthalpy and negative vacancy formation energy are found for YSH (yttria-stabilized hafnia) and YSZ (yttria- stabilized zirconia), suggesting the stability of both materials. Low activation energies (below 0.7 eV) of diffusion are found in both materials, and YSH’s is a little higher than that of YSZ. In addition, for both HfO2 and ZrO2 , the supercells with native oxygen vacancies are also studied. The so-called defect states are observed in the supercells with neutral and +1 charge native vacancy but not in the +2 charge one. It can give an explanation to the relatively lower activation energies of yttria-doped oxides and +2 charge vacancy supercells. A brief discussion is presented to explain the different YSH ion conductivities in the experiment and obtained by us, and we attribute this to the different ion vibrations at different temperatures. 相似文献
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Physics of the Solid State - On the basis of the constructed atomistic models of graphene/nanotube films with different numbers of nanotubes in supercells, in silico studies of the regularities of... 相似文献
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Thomas J. Kistenmacher 《Solid State Communications》1985,53(10):831-834
A crystallographic family tree can be developed for the (BEDT-TTF)2X salts which aids in the systematization and rationalization of the structural and electrical properties of this novel series of materials. Importantly, it is recognized that the ambient-pressure superconductor α-(BEDT-TTF)2I3 has a crystal structure coincident with the parent subcell of this crystallographic family tree. Moreover, all first-generation supercells (doubling of any one subcell vector) are exclusively populated by salts with non-centrosymmetric anions of tetrahedral symmetry, and apparently, second-generation supercells (doubling of any two subcell vectors) are populated by salts with centrosymmetric anions of octahedral symmetry. 相似文献
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Ruizhi Zhang Chunlei Wang Jichao Li Kun Yang Chao Zhang 《Solid State Communications》2008,145(5-6):299-302
Density functional calculations are used to investigate the role of Pb displacement in the formation of anti-ferroelectric phase in Pb(Mg1/3Nb2/3)O3. Order and disordered supercells, both are used. Through geometry optimization without symmetry imposed, the two supercells are found to be anti-ferroelectric. Displacement of cations are analyzed and it is shown that asymmetry of Pb’s next-nearest B-site shell is probably the reason for anti-parallel displacement of Pb. A–B-site, B-site–O bond distances and O6 octahedral volumes are also calculated. 相似文献
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《Micron (Oxford, England : 1993)》2001,32(2):141-146
Non-stoichiometric CuInS2 is a novel material for thin film solar cells. Electron energy loss spectrometry analysis shows that there are considerable lateral inhomogeneities on a scale of less than 100 nm. It is as yet unknown whether the Cu or In surplus comes in nanoprecipitates irregularly distributed in the otherwise stoichiometric matrix, or forms supercells where particular atoms are replaced by their complements. This question bears important consequences for the understanding of the local electronic structure and the mechanism of undesired recombination processes in the cell. Since the energy-loss near edge structure of ionisation edges (ELNES) mirrors the local density of unoccupied states it should be different in the two cases. We compare the sulfur L2,3 ELNES of a Cu-rich and of an In-rich specimen with simulations of supercells based on the telnes/wien97 code. Faint differences in the edge shape can be made visible using difference spectra. They agree reasonably well with simulations. The results show that the surplus species exists as a separate non-stoichiometric phase and not merely as a precipitate of elemental Cu or In. 相似文献