MI3(M=Bi,Sb,As)弹性和电子性质的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势计算方法,对比研究了菱方结构MI3(M=Bi,Sb,As)的弹性和电子性质.结果表明:SbI3的生成焓最低,较BiI3、AsI3更易生成.这三种材料都体现了弹性各向异性特征.SbI3是偏延性材料,BiI3和AsI3是脆性材料.高压下AsI3更容易被压缩.德拜温度的大小关系依次为SbI3>BiI3>AsI3.MI3(M=Bi,Sb,As)都是间接带隙半导体,电子的局域程度较强.在费米能级附近,I-5p轨道电子和金属M-s轨道电子发生杂化,形成共价键.MI3(M=Bi,Sb,As)中的化学键是共价键和离子键的混合.     

Devitrification characteristics of GexSe1−x glasses

Amorphous Ge_xSe_1?x compounds have been prepared and carefully characterized in the range 0 ? x ? 0.43 (density and micro-hardness measurements and DTA experiments). By heating samples from the amorphous phase, the crystallization process has been investigated for 0.15 ? x ? 0.30. An immiscibility gap in the vitreous region is determined by optical microscopy, from phase-separation observations; moreover, a new metastable crystalline phase appearing as an intermediate step between phase separation and stable GeSe₂ is described.     

X-ray investigation of the crystallization of chalcogenide glasses of the type (As2Se3)1−x:(Tl2Se)x

Amorphous and crystalline states of As₂Se₃, (As₂Se₃)₃ : Tl₂Se and As₂Se₃ : Tl₂Se have been studied using X-ray diffraction techniques. Structural changes arise during the process of annealing in the temperature range between their softening and melting points are reported and their rates investigated. The crystallization temperatures were found to be 105 ± 5 °C, 135 ± 5 °C and 180 ± 5 °C respectively. The unit cell parameters are identified for each of the three resulting crystalline phases, that for As₂Se₃ : Tl₂Se being orthorhombic while the other two are monoclinic.     

Crystal structure of α‴-(Zn1−x Cd x )3As2 (x = 0.26)

Single crystals of the α?-phase of (Zn_{1 ? x} Cd _x )₃As₂ solid solution (x = 0.26) have been prepared and investigated by X-ray diffraction analysis. The tetragonal unit-cell parameters are found to be a = b = 8.5377(2) Å, c = 24.0666(9) Å, sp. gr. I4₁/amd, Z = 16. Zn and Cd atoms in the crystal statistically occupy three symmetrically independent positions in the mirror planes and are tetrahedrally coordinated by arsenic atoms. (Zn,Cd) tetrahedra share edges to form a three-dimensional structure framework. The α?-phase is geometrically related to the fluorite structure. The character of arrangement of tetrahedral vacancies in fluorite-like unit cells is revealed. Chains of tetrahedral vacancies form microchannels oriented parallel the a and b axes, which pierce the three-dimensional structure framework at different levels along the c axis. The structure of α″-Cd₃As₂ crystals is found to be similar to that of α?-(Zn_0.74Cd_0.26)₃As₂.     

On the structure of amorphous GexTe1−x systems

Calculations have been made for the quadrupole splitting of a $\text{3}\text{2}$ spin state of Te¹²⁵ in an amorphous Ge_xTe_1?x system. The results favour the existence of a threefold coordinated black phosphorus structure with an excess of TeTe chains for x-values between o and 0.5; beyond 0.5, threefold coordinated GeTe and an excess of amorphous Ge coexist.     

Composition dependence of the refractive index and its photo-induced variation in the binary glass systems: Ge1−xSex and As1−xSex

The composition dependence of the refractive index and its photo-induced variation have been calculated for the Ge_1?xSe_x and As_1?xSe_x binary glass systems, using the random network model. It is found that the refractive index has a minimum in Ge_1?xSe_x at x = 0.8, while it shows a monotomic increase with increasing As content in As_1?xSe_x glasses. The refractive index of the Ge_1?xSe_x system decreases with illumination and the variation Δn of GeSe₂ is ?0.0316, while the refractive index of the As_1?xSe_x system increases with illumination and the variation of As₂Se₃ is 0.01. These results are in agreement with the experimental results reported by several workers.     

Intermetallic Compounds KnMm (М = Ag,Au, As,Sb, Bi,Ge, Sn,Pb): Geometrical and Topological Analysis,Cluster Precursors,and Self-Assembly of Crystal Structures

Crystallography Reports - A geometrical and topological analysis and simulation of the self-assembly of the crystal structures of intermetallic compounds formed in the K–M (M = Ag, Au, As,...     

Reaction of CpRu(PPh3)2Cl with six-member cyclothioethers. Structures of the [CpRu(PPh3) x L]Y complexes (L = pentamethylene sulfide, x = 2, Y = BF4 −; L = 1,3-dithiane; 1,3,5-trithiane, x = 2, Y = CF3SO3 −; L = 1,4-dithiane, x = 1, Y = BF4 −)

The synthesis of a series of ruthenium complexes with cyclothioether ligands is reported. The compounds were characterized by X-ray diffraction techniques. The molecular structures of [CpRu(PPh₃)₂(pms)]BF₄ (1), [CpRu(PPh₃)₂(1,3-dithiane)]OTfl (2), [CpRu(PPh₃)₂(1,3,5-trithiane)]OTfl (3), and [CpRu(PPh₃)(1,4-dithiane)]BF₄ (4) show chelation occurs only when the sulfur atoms are separated by at least two C atoms, creating a ligand bite size large enough to chelate. Cell parameters: 1, space group P2₁/c, a = 14.601(4), b = 19.102(10), c = 14.751(7) Å, β = 98.28(3)^○; 2, space group P2₁/c, a = 12.859(7), b = 15.576(3), c = 22.126(11) Å, β = 102.22(4)^○; 3, space group P2₁/c, a = 12.7320(20), b = 15.571(5), c = 22.287(4) Å, β = 101.812(14)^○; 4, space group Pbca, a = 11.2010(10), b = 16.321(7), c = 28.966(4) Å. Compounds 2 and 3 are X-ray isomorphous. The Ru–S bond lengths range from 2.341(3), 2.365(3) Å in compound 4 to 2.382(4) Å in compound 2. Upon chelation (compound 4), with subsequent loss of PPh₃, the Ru–P bond shortens to 2.327(3) Å. This may be due to reduced steric hindrance about the Ru atom. No evidence for C–S bond lengthening is observed.     

Effect of annealing on an amorphous GexTe1−x matrix with Te cristallites

Annealing shows very different behaviour for Te crystallites in an amorphous Ge_xTe_1?x matrix as a function of x (x = 0.1 … 0.5). For x ? 0.2, annealing at increasing temperatures increases the number (size) of the Te crystallites with subsequent GeTe + Te crystallization. However for x ? 0.3 there is first a disappearance of Te crystallites, then an appearance of GeTe crystallites, and subsequently GeTe + Te crystallization. Crystallites of either Te or GeTe act as extrinsic defects which add to the intrinsic ones. Activatioon energy decreases (increases) and conductance increases (decreases) as the number of defects increases (decreases). In all cases the final metallic state is obtained only when both GeTe and Te crystallites are present.     

RE∶YAP(RE=Nd,Tm)晶体缺陷与光谱分析

采用提拉法生长Nd∶YAP和Tm∶YAP晶体,利用吸收和荧光光谱表征样品。结果表明:经真空退火,提高了晶体质量。Nd∶YAP晶体在808 nm附近有较强的吸收,与商用激光二极管的发射波长匹配较好,获得了1064 nm荧光输出;Tm∶YAP晶体在790 nm附近有一定的吸收,在1.87μm处的荧光峰对应于3F4→3H6能级之间的跃迁,有利于激光的高能量调Q输出。     

Phase Diagrams of Semiconducting Compounds (III) Thermodynamic Calculation of the Ternary Melting Diagram of Ga?Al?As

The ternary phase diagram of Ga Al As has been calculated by VIELAND 'S method. The activity coefficients are determined using DARKEN 'S quadratic formalism for a ternary liquid in equilibrium with a regular solid solution. The agreement of calculation and experimental results is examinated using data from literature and solution measurements and liquid phase epitaxy experiments of this paper.     

Preparation of Al?Ga?P?As heterostructures

The present paper reports on the results of an investigation of crystallization of multilayer structures with a narrow-gap semiconductor surrounded by two wide-gap ones in the Al-Ga-P-As system on GaAs and GaP substrates. Influence of the lattice parameters' difference on the value of thermal stress in structures with a composition gradient was determined by the bend of structures separated from the substrate. It has been proved that with the P concentration in solid solutions being less than 1% heterojunctions with less tensions than in the Al–Ga–As system are available. A new method of obtaining Al_xGa_1–xP_yAs_1–y solid solutions with the concentration of P proportional to that of Al has been worked out on the basis of which multilayer heterolight-emitting structures have been prepared.     

A3BGa3Si2O14(A=Ca,Sr;B=Nb,Ta)晶体研究进展

介绍了一类性能优异、结构有序的新型材料--A3BGa3Si2O14(A=Ca,Sr;B=Nb,Ta)单晶,总结了其研究进展,并对该类晶体的生长、结构、热学、光学和压电性能进行了描述.     

Janus型二维磁电材料CrXX’(X/X’=S,Se,Te)第一性原理研究

自石墨烯被发现以来,各种具有新奇特性的二维材料受到了越来越多的关注。Janus型二维材料具有不对称的表面特性,这种特殊的结构往往具有独特的电学、磁学与光学性质,使其成为近年来材料科学领域研究的热点。本文搭建了Janus型结构CrXX’(X/X’=S,Se,Te)(CrSSe, CrSTe, CrSeTe),研究了体系的电学、磁学、光学性质,并探究了双轴应变对其电学、磁学、光学性质的影响。结果表明,CrSSe、CrSTe与CrSeTe均呈现金属性,都是电子的优良导体,三种体系的电子结构对外加应变具有很好的鲁棒性。CrXX’(X/X’=S,Se,Te)具有本征铁磁性,并且通过施加双轴应变可对其磁矩进行调控。此外,三种体系均具有较高的居里温度,特别是CrSTe的居里温度可达310 K。CrXX’(X/X’=S,Se,Te)还具有优异的可见光与紫外光吸收性能,应变可对其光吸收系数进行调控,并且压应变与拉应变可分别使其吸收谱线向短波与长波方向移动。本文的工作为进一步研究二维Janus单层CrXX’(X/X’=S,Se,Te)在新型室温自旋电子器件领域的应用提供了理论支持。     

AlxGa1−xN bulk crystal growth: Crystallographic properties and p–T phase diagram

The recent results on the growth of the Al_xGa_1−xN bulk single crystals (0.22≤x≤0.91) from solution in liquid Ga under high nitrogen pressure are discussed. We focus on the influence of temperature and the choice of the Al source on the crystal growth. The experiments involving different sources of aluminum such as Al metal, pre-reacted polycrystalline Al_yGa_1−yN and AlN powder are compared. The best results were achieved using pre-reacted polycrystalline Al_yGa_1−yN or/and AlN. Single-crystal structure refinement data of these Al_xGa_1−xN crystals are presented. We also update the p–T phase diagram of (Al,Ga)N compound at high N₂ pressure for various Al content, which is the basis for (Al,Ga)N synthesis.     

Template free-solvothermaly synthesized copper selenide (CuSe,Cu2−xSe, β-Cu2Se and Cu2Se) hexagonal nanoplates from different precursors at low temperature

Nonstoichiometric (Cu_2−xSe) and stoichiometric (CuSe, β-Cu₂Se and Cu₂Se) copper selenide hexagonal nanoplates have been synthesized using different general and convenient copper sources, e.g. copper chloride, copper sulphate, copper nitrate, copper acetate, elemental copper with elemental selenium, friendly ethylene glycol and hydrazine hydrate in a defined amount of water at 100 °C within 12 h adopting the solvothermal method. Phase analysis, purity and morphology of the product have been well studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray diffraction (EDAX) techniques. The structural and compositional analysis revealed that the products were of pure phase with corresponding atomic ratios. SEM, TEM and HRTEM analyses revealed that the nanoplates were in the range 200–450 nm and the as-prepared products were uniform and highly crystallized. The nanoplates consisted of {0 0 1} facets of top–bottom surfaces and {1 1 0} facets of the other six side surfaces. This new approach encompasses many advantages over the conventional solvothermal method in terms of product quality (better morphology control with high yield) and reaction conditions (lower temperatures). Copper selenide hexagonal nanoplates obtained by the described method could be potential building blocks to construct functional devices and solar cell. This work may open up a new rationale on designing the solution synthesis of nanostructures for materials possessing similar intrinsic crystal symmetry. On the basis of the carefully controlled experiments mentioned herein, a plausible formation mechanism of the hexagonal nanoplates was suggested and discussed. To the best of our knowledge, this is the first report on nonstoichiometric (Cu_2−xSe) as well as stoichiometric (CuSe, β-Cu₂Se and Cu₂Se) copper selenide hexagonal nanoplates with such full control of morphologies and phases by this method under mild conditions.     

CF4气氛中生长Re: LiM(Re=Tm,Ce;M=Lu,Y)F4晶体

本文在CF4气氛中以提拉法成功地生长出高质量的掺入Tm3+、Ce3+的LiLuF4和LiYF4晶体,对比了Ar和CF4气氛中生长的LiYF4晶体的红外光谱特性,讨论了CF4气氛对LiM(M=Y,Lu)F4晶体生长的影响.同时测试了Tm3+、Ce3+在LiLuF4和LiYF4晶体中的有效分凝系数,从离子半径和晶胞畸变的角度,讨论了Tm3+、Ce3+在LiLuF4和LiYF4晶体中有效分凝系数差别的产生原因.     

Crystal structures of (η5-C5H4COMe)M(CO)3Me (M=Mo,W)

The crystal structures of ( ⁵-C₅H₄COMe)M(CO)₃Me (M=Mo,W) have been determined. They are not isostructural. M=Mo isP2₁/c,a=10.205(6),b=14.192(8),c=8.135(6) Å,=93.43(4)° andD(calc)=1.71 g cm^–3 forZ=4. M=WisP2₁/c,a=12.580(7),b=6.830(5),c=13.750(7) Å,=93.72(4)° andD(calc)=2.20 g cm^–3 forZ=4. Both have a four-legged piano stool geometry with the substituted carbon making the closest M-C( ⁵) approach. The methyl group in the M=W derivative is disordered between twotrans-ligand positions. The average bonding parameters for the more accurately determined Mo analog are: Mo-C()⁵)=2.34(3) Å, Mo-CO=1.98(2) Å, Mo-Me=2.304(4) Å.     

Change of short-range order with temperature and composition in liquid GexSe1−x as shown by density measurements

Density measurements were performed on melts of the binary chalcogenide system Ge_xSe_1?x (0 ? x ? 0.5) up to 1000°C. The isotherm of molar volumes V_m at 750°C shows a relative maximum near GeSe₂. Molar volumes of the system behave linearly between GeSe and Se at 1000°C. V_m's of melts between x = 0.30 and x = 0.35 decrease at high temperatures on heating. The anomalous density behaviour of the melts clearly shows a change of short-range order from a less to a more densely packed structure, caused by the development of a pσ-bonding system. Within the composition range $\text{0 ? x ?}\text{1}\text{3}$ the short-range order at lower temperatures is determined mainly by $\text{GeSe}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}$ tetrahedra linked directly corner-to-corner or via Se atoms. At higher temperatures pσ bonds arise more and more, even in melts rich in selenium. Within the composition range $\text{1}\text{3}\text{? x ? 0.5}$ the short-range order is mainly determined by a distorted octahedral configuration, even at lower temperatures. From the short-range orders of melts and from crystalline structures of GeSe₂ and GeSe, the tendency of glass formation from the melt is discussed in detail.