共查询到20条相似文献,搜索用时 424 毫秒
1.
利用密度泛函理论和k·p模型方法对半哈斯勒化合物XYZ(X=Li,Na,K;Y=Ag,Au;Z=S,Se,Te)进行了研究.半哈斯勒化合物XYZ可以看作是由Xn+离子填充到闪锌矿YZn-晶格组成.它们的s态电子形成双重简并Γ6((2))能带,p-d杂化态形成双重简并Γ7((2))能带和四重简并Γ8((4))能带.当s型的Γ6((2))能带高于Γ7((2))和Γ8((4))能带时,化合物为普通绝缘体.然而,当s型Γ6((2))能带低于Γ7((2))和Γ8((4))能带时,化合物是拓扑非平庸绝缘体(如NaAuS)或半金属(如NaAuTe),这还要取决于负或正... 相似文献
2.
3.
4.
本文使用基团理论计算KB5O8·4HO2O(简称KB5)晶体的倍频系数,得到d31=2.61×10-10esu,d32=007×10-10esu,d33=3.26×10-10esu,与实验值符合较好。计算结果表明:氢键对KB5晶体的倍频系数有影响。本文还分析了KB5晶体倍频系数小的起因,除去[B5O6(OH)4]-1基团的微观倍频系数小外,还在于基团的空间排列方式不利,导至最大的微观倍频系数X123相互抵消。最后,本文提出了在含四配位硼原子的硼氧化合物中寻找倍频新材料的结构判据。
关键词: 相似文献
5.
6.
7.
1974年作者提出了“非线性光学效应的离子基团理论”^[1],并据此对钙钛矿型等体系的倍频系数作了理论计算,得到了很好的结果。本文进一步使用作者1981年建议的“晶体倍频系数的平均能带近似计算法”^[2],从能带理论出发计算了钙钛矿型晶体的倍频系数。计算结果表明:(1)由“平均能带近似法”仍可得到“钙钛矿型晶体倍步效应基团理论”^[1]的几个基本论点,并给出后者的近似等级;(2)充分揭示了SrTiO3、KTaO3晶体电场感应倍频系数χ333^(2ω)/χ311^(2ω)比值的变化与中心B离子的相对位移、能带结构、B-O键离子性之间的关系;(3)通过倍频系数和能带结构关系的研究,有可能把晶体倍频系数作为检验能带结构是否正确的一个新的数据;(4)由本文的计算公式,可以计算出在外电场作用下中心B离子相对于配位体氧原子的位移量△Z,并和外电场作用下的感应自发极化Ps的实验值相一致。 相似文献
8.
用最小偏向角法在20℃下精确测量了0.62Pb(Mg1/3Nb2/3)O3< /sub>-0.38PbTiO3( 0.62PMN-0.38PT)单晶的折射率,给出了该温度下折射率色散的Sellmeier方程.研究了能带 结构与折射率的关系,计算了样品的Sellmeier光学系数:对no,E0=5.50eV,λ0=0.2 26μm,S0=1.004×1014m-2,Ed=28.1 0eV;对ne,E0=5.57eV,λ 0=0.223μm,S0=1.017×1014m-2,Ed=28.10eV.A BO3型钙钛矿材料中,BO6八面体基元决定了晶体的能带结构,对折 射率产生重要影响.
关键词:
PMNT单晶
折射率
Sellmeier光学系数 相似文献
9.
10.
11.
K. Thoma 《Zeitschrift für Physik A Hadrons and Nuclei》1968,211(3):218-234
The thermal equation of state is investigated for polar crystals (zinc blende and wurtzite structures). A finite crystal is considered with free charges to compensate the dipole moment of the crystal in equilibrium. The free energy is taken in the quasiharmonic approximation. A simple point-charge model for zinc oxide leads to the thermal expansion coefficients and pyroelectric constants, and to the elastic moduli, piezoelectric moduli and dielectric susceptibilities. 相似文献
12.
Polytypism in GaAs nanowires: determination of the interplanar spacing of wurtzite GaAs by X‐ray diffraction 下载免费PDF全文
Martin Köhl Philipp Schroth Andrey A. Minkevich Jean‐Wolfgang Hornung Emmanouil Dimakis Claudio Somaschini Lutz Geelhaar Timo Aschenbrenner Sergey Lazarev Daniil Grigoriev Ullrich Pietsch Tilo Baumbach 《Journal of synchrotron radiation》2015,22(1):67-75
In GaAs nanowires grown along the cubic [111]c direction, zinc blende and wurtzite arrangements have been observed in their stacking sequence, since the energetic barriers for nucleation are typically of similar order of magnitude. It is known that the interplanar spacing of the (111)c Ga (or As) planes in the zinc blende polytype varies slightly from the wurtzite polytype. However, different values have been reported in the literature. Here, the ratio of the interplanar spacing of these polytypes is extracted based on X‐ray diffraction measurements for thin GaAs nanowires with a mean diameter of 18–25 nm. The measurements are performed with a nano‐focused beam which facilitates the separation of the scattering of nanowires and of parasitic growth. The interplanar spacing of the (111)c Ga (or As) planes in the wurtzite arrangement in GaAs nanowires is observed to be 0.66% ± 0.02% larger than in the zinc blende arrangement. 相似文献
13.
14.
The complete piezoelectric tensors of both the wurtzite and zinc blende polymorphs of ZnO and ZnS have been computed by ab initio periodic linear combination of atomic orbitals (LCAO) methods, based mainly on the Hartree-Fock Hamiltonian, with an all-electron Gaussian-type basis set. The computational scheme was based on the Berry phases theory, yielding directly the proper piezoelectric stress coefficients eik=(∂Pi/∂εk)E; also the strain coefficients dik=(∂εk/∂Ei)τ were obtained, by intermediate calculation of the full elasticity tensors of all four crystals. In particular, the e15 wurtzite shear constants were included for the first time in such calculations. A careful study of the clamped-ion and internal-strain piezoelectric components shows that the latter ones are well simulated by classical point-charge calculations including quantum-mechanical structural relaxation. The much larger piezoelectric response of ZnO with respect to ZnS is explained by analysing signs and ratios of the respective clamped-ion and internal-strain components. 相似文献
15.
Electron spin resonance and optical absorption measurements are reported for Co2+ in structurally pure single crystals of cubic, hexagonal, and 4H polytype ZnS. Co2+ spectra corresponding to the four different cation sites expected for these structures were observed, i.e. a cubic center from zinc blende, an axial center from wurtzite, and two different axial centers from the 4H polytype host. The energy of the optical 4A2-4T2 transition and the spin Hamiltonian parameters show characteristic differences for these four centers, which are discussed. 相似文献
16.
Structural, electronic and optical properties as well as structural phase transitions of ternary alloy CdxZn1 − xS have been investigated using the first-principles calculations based on the density functional theory. We found that the crystal structure of CdxZn1 − xS alloys transforms from wurtzite to zinc blende as Cd content of x=0.83. Effect of Cd content on electronic structures of CdxZn1 − xS alloys has been studied. The bandgaps of CdxZn1 − xS alloys with wurtzite and zinc blende structures decrease with the increase of Cd content. Furthermore, dielectric constant and absorption coefficient also have been discussed in detail. 相似文献
17.
M. Rabah D. Rached R. Khenata N. Moulay A. Zenati 《Solid State Communications》2009,149(23-24):941-945
We report local density functional calculations using the full potential linear muffin-tin orbital (FP-LMTO) method for binary platinum nitride (PtN), in five different crystal structures, the rock salt (B1), zinc-blende (B3), wurtzite (B4), nickel arsenide (B8), and PbS (B10) phases. The ground state properties such as the equilibrium lattice constant, elastic constants, the bulk modulus and its pressure derivative of PtN in these phases are determined and compared with the other available experimental and theoretical works.Our calculations confirm in the B3 structure that PtN is found to be mechanically stable with a large bulk modulus B=232.45 GPa and at a sufficiently high pressure the B81 structure would be favoured.The theoretical transition pressure from zinc blende (B3) to NiAs (B81), zinc-blende (B3) to rock-salt (B1) and zinc-blende (B3) to PbO (B10) is determined to be 9.10 GPa, 9.85 GPa and 69.35 GPa, respectively. Our calculation shows also in five different structures for PtN a high bulk modulus is a good indicator of a hard material. 相似文献
18.
K. Thoma 《Zeitschrift für Physik A Hadrons and Nuclei》1968,209(2):175-187
The thermal equation of state is investigated for polar crystals (zinc blende and wurtzite structures). As a model, a finite diatomic linear chain is considered with surface charges to compensate the dipole moment of the chain. Within the quasiharmonic approximation for the free energy the electro-mechanical constants are evaluated up to third order. 相似文献
19.
采用同步辐射能量色散X射线衍射(EDEX)技术和金刚石对顶砧高压装置,对纳米硫化锌球壳进行了原位高压X射线衍射实验。最高压力达33.3 GPa。常压下纳米硫化锌球壳为纤锌矿结构和闪锌矿结构共存的混相结构。压力达到11.2 GPa时,纳米硫化锌空心球中的纤锌矿结构全部转变为闪锌矿结构。压力达到16.0 GPa时,发生了由闪锌矿结构向岩盐矿结构的相变,在17.5 GPa和21.0 GPa时分别出现未知峰,33.3 GPa时基本完全转变为岩盐矿结构。两个相变均为可逆相变。 相似文献
20.
Abstract The dependence of the pressure threshold of martensitic transformations on the disordering degree of starting structures is considered for graphite-like BN into diamond-like BN modifications transitions. The effect of loading conditions on transformation mechanisms of rhombohedral BN into zinc blende or wurtzite modifications is analyzed also. Analytical relations obtained allow to explain the experimental data and to predict a behavior of various graphite-like structures under different p, T conditions. 相似文献