排序方式: 共有116条查询结果,搜索用时 755 毫秒
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采用基于密度泛函理论框架下的第一性原理超原胞方法和虚晶近似方法, 在局域密度近似和广义梯度近似下, 对四方和正交以及单斜相K0.5Na0.5NbO3的能量和原子结 构以及电子结构进行了系统的研究. 计算结果表明三种K0.5Na0.5NbO3相的能量差别较小, 这与实验上它们之间容易发生相转化是一致的. 进一步发现单斜相的能量比四方相和正交相低, 说明单斜相结构更加稳定, 并且理论计算的结构参数与实验值符合得很好. 电子结构结果也表明单斜相的键合作用比四方相和正交相键合作用更强, 进一步说明单斜相结构更加稳定.
关键词:
铌酸钾钠
四方相
单斜相
密度泛函理论 相似文献
43.
We simulate the spectrum characteristics of fibre Bragg grating (FBG) with non-uniform temperature using the transmission matrix method, and the results are analysed. It is found that firstly the modulated coefficient of average refractive index is a very important parameter that influences the spectrum characteristic of the fibre Bragg grating, and secondly the spectrum curves are different in different temperature fields at the same parameter. Hence, we can determine the metrical temperature by analysing the spectrum of fibre Bragg grating. 相似文献
44.
The geometrical and electronic structures of nitrogen-doped β-SiC are investigated by employing the first principles of plane wave ultra-soft pseudo-potential technology based on density functional theory. The structures of SiC1-xNx (x = 0, 1/32, 1/16, 1/8, 1/4) with different doping concentrations are optimized. The results reveal that the band gap of β-SiC transforms from an indirect band gap to a direct band gap with band gap shrinkage after carbon atoms are replaced by nitrogen atoms. The Fermi level shifts from valence band top to conduction band by doping nitrogen in pure β-SiC, and the doped β-SiC becomes metallic. The degree of Fermi levels entering into the conduction band increases with the increment of doping concentration; however, the band gap becomes narrower. This is attributed to defects with negative electricity occurring in surrounding silicon atoms. With the increase of doping concentration, more residual electrons, more easily captured by the 3p orbit in the silicon atom, will be provided by nitrogen atoms to form more defects with negative electricity. 相似文献
45.
The title compound was obtained by the flux method and its structure was determined.It crystallizes in monoelinic,space group P2/c with a=11.0024(17).b=9.2979(14),C=14.500(2)(A),β=110.879(2)°.V=1385.9(4)(A)3,Z=4,Mr=908.38,F(000)=1592,=19.601 mm-1,Dc=4.353 g/cm3,the final R=0.0481 and wR=0.1257 for 2532 observed reflections with I>2σ(I).The Rb3La3(BO3)4 structure Can be viewed as a 3-dimensional scaffold-like framework constructed by La-O polyhedra and BOs groups.Two Rb+ ions locate in a channel along the a direction and the rest one in a cavity. 相似文献
46.
采用原位合成法制备了聚甲基丙烯酸甲酯包覆MAPbBr3纳米晶(MAPbBr3@PMMA,MA=甲铵离子)静电纺丝膜。当氨气(NH3)通入MAPbBr3@PMMA纤维膜时与MAPbBr3中的MA发生取代,能显著降低MAPbBr3@PMMA纤维的荧光强度,以此构建了基于MAPbBr3@PMMA纤维荧光猝灭的NH3传感器。通过扫描电镜、透射电镜、粉末X射线衍射和红外对静电纺丝膜的形貌和结构进行表征,通过紫外可见光谱、荧光光谱对其光学特性进行表征。结果表明,传感器的荧光强度与NH3浓度在8~90 mg·L-1之间呈现出良好的线性关系(r=0.995 9),NH3的检出限低(3 mg·L-1),且具有良好的重现性和选择性。在实际样品气体的测定中,加标回收率为92.2%~102.1%,相对标准偏差(RSD)为1.8%~3.2%。 相似文献
47.
WANG Mao-Sheng 《理论物理通讯》2009,52(1):81-84
Effects of coupling distance on synchronization and coherence of chaotic neurons in complex networks are numerically investigated. We find that it is not beneficial to neurons synchronization if confining the coupling distance of random edges to a limit dmax but help to improve their coherence. Moreover, there is an optimal value of dmax at which the coherence is maximum. 相似文献
48.
Structural and electrical properties of Nd ion modified lead zirconate titanate nanopowders and ceramics 下载免费PDF全文
A modified sol-gel method is used for synthesizing Nd ion doped
lead zirconate titanate nanopowders Pb1 - 3x/2NdxZr0.52Ti0.48O3 (PNZT) in an ethylene
glycol system with zirconium nitrate as zirconium source. The
results show that it is critical to add lead acetate after the
reaction of zirconium nitrate with tetrabutyl titanate in the
ethylene glycol system for preparing PNZT with an exact fraction of
titanium content. It has been observed that the dopant of excess Nd
ions can effectively improve the sintered densification and activity
of the PNZT ceramics. Piezoelectric, dielectric and ferroelectric
properties of the PNZT ceramics are remarkably enhanced as compared
with those of monolithic lead zirconate titanate (PZT).
Especially, the supreme values of piezoelectric constant (d33)
and dielectric constant (\it ε) for the PNZT are both
about two times that of the monolithic PZT and moreover, the remnant
polarization (Pr) also increases by 30%. According to
the analysis of the structures and properties, we attribute the
improvement in electrical properties to the lead vacancies caused by
the doping of Nd ions. 相似文献
49.
间隙高度对涡轮叶顶间隙流动的影响 总被引:6,自引:0,他引:6
叶顶间隙流动是导致涡轮动叶中产生流动损失的主要原因之一.对某动力涡轮第一级内三维流动的数值计算结果表明,流体在经过动叶叶顶间隙以后在约25%叶顶轴向弦长处(τ=3mm)在叶顶与吸力边夹角处卷起形成间隙涡,造成流动阻塞,同时在间隙内叶片顶部10%叶顶轴向弦长处(τ=3mm)开始在压力边出现叶顶分离涡,使得间隙流动损失增加.随着间隙高度增大,通过间隙的流量增加,间隙涡形成位置后移,间隙涡、叶顶分离涡尺寸变大,在流道内影响范围增大,导致流动损失变大. 相似文献
50.
Dielectric properties of SiC/Ni nanocomposites prepared by a simple and facile electroless plating approach at X band are investigated. Compared to the original SiC nanopartieles (SiCp), the real part of the permittivity, ε', and the dielectric loss tangent tang δe of SiC/Ni nanocomposites are clearly enhanced by about 31% and 33%, respectively. The effective equations for complex permittivity of SiC/Ni nanoeomposites are proposed. We also calculate ε' and tan δe of SiC/Ni nanoeomposites and the calculated results are well consistent with the measured data. 相似文献