共查询到20条相似文献,搜索用时 744 毫秒
1.
2.
古新安 朱韦臻 罗志伟 ANGELUTS A A EVDOKIMOV M G NAZAROV M M SHKURINOV A P ANDREEV Y M LANSKII G V SHAIDUKO A V KOKH K A SVETLICHNYI V A 《中国光学》2012,5(1):57-63
从GaSe∶AgGaSe2熔体(质量掺杂浓度为10%)中生长的非线性光学晶体ε-GaSe∶Ag晶体(质量掺杂浓度≤0.04%)是一种非中心对称晶体,可用于相位匹配频率转换。Ag的掺入使GaSe晶体的显微硬度提高了30%,从而使其可以在任意方向上进行切割和抛光。本文研究了GaSe∶AgGaSe2晶体在可见、中红外及太赫兹波段的光学性能。实验证明:GaSe∶AgGaSe2晶体的吸收系数是纯GaSe晶体的2倍,其CO2激光倍频效率是ZnGeP2晶体的1.7倍。 相似文献
3.
稀土正铁氧体YFeO3呈正交钙钛矿结构,其晶体和纳米晶材料在电极材料、 传感器和光催化领域具有重要的应用价值.用平面波赝势方法,采用广义梯度近似、改进的Perdew-Burke-Emzerhof交换-关联势、 实空间超软赝势计算方案,研究了YFeO3晶体的几何结构、电子结构和光学性质. 计算得到的晶格参量与报道的实验结果一致.通过对能带结构、态密度、介电函数、吸收系数和光电导率的计算和分析, 确定YFeO3是直接能隙半导体,能隙Eg约为2.22 eV,阐明了YFeO3晶体和纳米晶具有较好的可见光催化性能. 相似文献
4.
5.
6.
产生蓝色相干辐射和实现Nd:YAG 1.0642μm倍频90°非临界相位匹配的Nb:KTiPO4 总被引:1,自引:1,他引:0
本文报道了用熔盐顶部籽晶法生长Nb浓度(0~13)mol%的Nb:KTP晶体的倍频的Ⅱ型相位匹配的截止波长和Nd:YAG1.0642μm及Nd:YA1O31.0795μm激光在这些晶体中倍频的最佳相位匹配角的测量结果.从中可看出,由于Nb5+的引入使KTP晶体倍频的Ⅱ相位匹配的截止波长有效蓝移,目前已使截止波长蓝移至937nm且有效产生468.5nm的倍频蓝光.同时Nb5+的引入使Nd:YAG1.0642μm激光和Nd:YA1O3倍频的最佳相位匹配方向产生很大的变化,目前已使Nb:KTP晶体倍频的最佳相位匹配方向为θ=88.32°、Φ=0°,非常接近于90°非临界相位匹配方向. 相似文献
7.
8.
9.
这篇论文是作者之一的某一篇论文的继续。论文分四节。在第一节中我们讨论的对象是应用二元混合气体的买厄理论至一个在AB型晶体上的二元固溶体而获得的不可约集团积分B(v1,v2)。我们严格地证明了它们是某一些晶体常数z1,z2,…的线性函数。这些常数的定义为1/((1/2)N)∑λabλa′b′…,式中N代表晶点阵的点的总数,λab为邻矩阵,定义为λab=1 如果ab为近邻, =0,如果ab不是近邻, a,a′,…互不相等,b,b′,…也互不相等,而乘积λab…为全部下标的一个不可约乘积。证明共用了三个定理,同时也援用了一个所谓基本不可约集团的定义。在第二节中,我们应用了第一节的讨论对B(2,3)作了计算。在第三节中,我们应用第一节的结果,简化了求固溶体自由能的Kirkwood方法,同时也利用了简化的方法求得了自由能对(kT)-1展开的幂级数中(kT)-7的系数。比(kT)-7更早的项的系数早已在作者之一的一篇论文中求得。在第四节中,我们利用第一节的结果,证明了严格理论在忽略z2,z3,…时即成了Bethe理论的第一级近似。如果将自由能表为z1,z2,…的函数而称它们的系数为f1,f2,…,那末我们指出:只消研究在某些赝点阵上的固溶体的配分函数,便可以求出f1,f2,…,同时我们也指出:在这些赝点阵上的固溶体的配分函数是可以(而也容易)严格地求出的,因此以上的理论供给了我们一个较好的求固液体的自由能的方法。 相似文献
10.
11.
R.?V.?Vedrinski? V.?L.?Kra?zman M.?P.?Lemeshko E.?S.?Nazarenko A.?A.?Novakovich L.?A.?Reznichenko V.?N.?Fokin V.?A.?Shuvaeva 《Physics of the Solid State》2009,51(7):1394-1398
The local atomic structure of PbTiO3, BaTiO3, and KNbO3 perovskite-type crystals and K x Na1 ? x NbO3 solid solutions in different phases is investigated using the angular dependence of the pre-edge structure of the Ti and Nb K X-ray absorption spectra and the EXAFS data. In noncubic phases, a considerable deviation of the local structure from the structure determined from diffraction data is observed only for the tetragonal phase of the BaTiO3 crystal. It is revealed that, in the cubic phase of niobates, the niobium atoms are characterized by significant displacements from the centrosymmetric positions along the threefold axes, so that they are close in the magnitude and the direction to the displacements in the low-temperatures rhombohedral phases. 相似文献
12.
F. Romain P. Tougard B. Pasquier N. Le Calvé A. Novak A. Péneau 《Phase Transitions》2013,86(4):259-274
Abstract Structural phase transitions in 3,5-dichloropyridine crystal have been studied by calorimetry (150–300 K), X-ray diffraction (300 K), 35Cland 14N nuclear quadrupole resonance (75–300 K) and vibrational spectroscopy (20–300K). Three phases have been shown to exist: phase I, between 338 and 287.5 K, phase 11, between 287.5 and 167.5 K, and phase 111, below 167.5 K. Phase I is characterised by the space group P 2,/m and Z = 2 whereas phases I1 and 111 remain centrosymmetric but double the unit cell. All the phases are ordered and contain crystallo- graphically equivalent molecules. The I ? I1 transition is of first order and probably of the reconstructive type while the II ? III transition is believed to be displacive. Both transitions are monitored by predominantly R′x and R′z librational motions. 相似文献
13.
Theoretical expressions for the overall values of the conventional discrepancy indicesR(F) andR(I) are derived for a non-centrosymmetric crystal with a centrosymmetric group by taking the centrosymmetric group and a part
of the other atoms in the unit cell as the trial structure. These results are used to obtain tables of values of these indices
in terms of the parameter σ
1c
2
and σ
1
2
which define the fractional contribution to the local mean intensity from the centrosymmetric group and all the known atoms
respectively.
Contribution No. 561 相似文献
14.
Sophie Quillard Jean‐Yves Mevellec Philippe Deniard Jean‐Michel Bouler Jean‐Pierre Buisson 《Journal of Raman spectroscopy : JRS》2016,47(8):971-977
Polarized Raman measurements were recorded on a monoclinic brushite (CaHPO4.2H2O) crystal in the 800–1200 cm−1 spectral range, corresponding to the P O stretching modes. This study is a continuation of the investigation of the phosphate stretching modes observed in polarized infrared reflectance spectra of brushite crystal. In such ionic non‐centrosymmetric crystals, the splitting between the transverse and longitudinal components of the optic vibrations was observed in the polarized Raman spectra recorded at several scattering geometries. A″ symmetry modes of the brushite crystal were measured. Using a simple model based on the symmetry of the PO4 group, the Raman intensities of the stretching modes are calculated and compared with experimental bands. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
15.
Mutsumi Sugiyama Minoru Kinoshita Hisayuki Nakanishi 《Journal of Physics and Chemistry of Solids》2005,66(11):2127-2129
The crystal structure and phase transition of ZnInGaS4 were described. The ZnInGaS4 had both a defect chalcopyrite and a layered structure below 920 °C, and only the layered structure ZnInGaS4 existed between 920 and 1020 °C. The layered structure ZnInGaS4 was grown using the normal freezing method. The bandgap of the layered structure ZnInGaS4 was estimated to be approximately 2.6 eV and it is possibly a direct bandgap. This is a first step toward realizing the novel functions of ZnInGaS4. 相似文献
16.
D. P. Kozlenko N. T. Dang S. E. Kichanov The-Long Phan N. V. Dang L. H. Khiem E. V. Lukin B. N. Savenko 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2016,10(2):370-374
The crystal structure of iron-doped barium titanate BaTi1–x Fe x O3 is studied by neutron diffraction in the range of 0 ≤ x ≤ 0.12. At low concentrations of iron, x < 0.01, and at room temperature, these compounds have a polar structure with tetragonal symmetry with space group P4mm. The temperature of the transition of the tetragonal ferroelectric phase into the cubic paraelectric phase with space group Pm \(\bar 3\) m for an iron concentration of x = 0.01 is 390 K (for pure BaTiO3, it is 410 K). At an iron concentration of x = 0.07, the crystal structure of the studied compounds varies, and it is described by the centrosymmetric hexagonal space group P63/mmc. The structural parameters of various phases of compound BaTi1–x Fe x O3 are determined from the experimental data. 相似文献
17.
Shih -Lin Chang 《Applied Physics A: Materials Science & Processing》1981,26(4):221-226
A direct experimental method is described for the phase determination of x-ray reflections from single crystals. This method utilizes the coherent dynamical interaction of diffracted x-ray beams in a 3-beam multiple Bragg reflection to reveal the signs,S
P, of triplet-phase products. This dynamical effect and the relative rotation of the crystal lattice with respect to the Ewald sphere are considered. The phase dependence of the reflected intensity profile is observed and is in agreement with the theory. It is found thatS
P=S
L ·S
R,S
L being the sign defined from the multiple diffraction line profile.S
R is determined by the rotation of the crystal lattice relative to the Ewald sphere. The new method can be applied to a direct experimental determination of phases without carrying out the complicated dynamical calculations.On leave from Instituto de Fisica, Universidade Estadual de Campinas, Campinas, S.P. 13100, Brazil 相似文献
18.
B. B. Koleva R. Nikolova S. Zareva T. Kolev R. W. Seidel H. Mayer‐Figge W. S. Sheldrick 《Journal of Physical Organic Chemistry》2009,22(8):726-734
The novel pyridyl‐substituted coumarin ( 1 ) and its perchlorate salt ( 2 ) have been synthesized and their structure and properties elucidated in detail spectroscopically, thermally and structurally, using single crystal X‐ray diffraction for 2 , linear‐polarized solid state IR‐spectroscopy, UV‐spectroscopy, TGA, DSC, DTA, and positive and negative ESI MS. Quantum chemical calculations were used to obtain the electronic structure, vibrational data and electronic spectra. The studied compound crystallizes in the centrosymmetric space group P‐1 and exhibits an infinite layered structure with the ions linked by means of the intermolecular N+H…OClO3 (2.795 Å) interactions. The cations are disposed in a manner leading to a significant π‐stacking effect with a distance of 2.980 Å. The effects of Npy protonation on the optical and magnetic properties are elucidated by comparing the data of the protonated and neutral compounds. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
19.
In an ultrahigh vacuum system (10?10 torr) LEED, Auger spectroscopy, flash desorption and work-function measurements have been used to follow the kinetics of adsorption of carbon monoxide on the (100) face of a molybdenum single crystal. At room tempeiature CO adsorbs into three β states β1, β2, β3, which are associated with different work-function changes: the phase β3 is found to correspond to a decrease of work-function whereas the phases β1 and β2 correspond to an increase. The total change of surface potential is about 0.50 eV at saturation. An ordered C (2×2) structure is found for the β2 + β3 phases, and is associated at their maximum coverage (about half a monolayer) with a work-function change of + 0.070 eV with respect to the clean surface. At completion of the monolayer a P (1×1) structure is observed. 相似文献
20.
In this paper we demonstrate that two independent methods of calculations (DFT based ab initio and semi-empirical crystal field theory) can be used to form a complementary picture of the optical and electronic properties of the doped host and impurity ion. The crystals considered in the present paper are: (i) YAlO3:Ce3+ and (ii) two dominant phases of TiO2—rutile and anatase. As an example, detailed calculations of the band structure and crystal field energy level scheme of YAlO3:Ce3+ are reported. From the analysis of the band structure and density of states, the character of the YAlO3 energetic bands and positions of the Ce impurity energy levels were established. It was also shown how the ab initio methods can be used for calculations of the structural properties of solids under elevated pressure. Taking the two dominant phases of TiO2 as an example, it was demonstrated how the elastic properties can be extracted from the calculated unit cell’s volume at different pressures. Particular attention was paid to the microscopic effects of crystal field, which were evidenced by the pressure-induced changes of the structure and shape of distribution of the Ti 3d electrons density of states. It was demonstrated how the difference in crystal structure of the anatase and rutile phases leads to remarkable difference in microscopic crystal field effects, which was explained by different Ti-O distances in both phases. In addition, the pressure dependence of the band gaps for anatase and rutile was investigated. It was shown that the hydrostatic pressure leads to the band gap narrowing in anatase and band gap widening in rutile, with pressure coefficients +0.00681 eV/GPa for rutile and −0.0088 eV/GPa for anatase. 相似文献