SIERPINSKI GASKET晶格上具有次近邻相互作用高斯模型的临界行为

利用等效变换和重正化群变换的方法,在Sierpinskigasket晶格上研究了具有近邻和次近邻相互作用Gaussian模型的临界性质,求出了临界温度和关联长度临界指数．结果表明：在相变点近邻相互作用K1和次近邻相互作用K2之间满足一定的关系,这种关系对铁磁体和反铁磁体都适用．并且考虑次近邻相互作用后,临界温度和临界指数都不发生改变．     

A Solvable Decorated Ising Lattice Model

A decorated lattice is suggested and the Ising model on it with three kinds of interactions K₁, K₂, and K₃ is studied. Using an equivalent transformation, the square decorated Ising lattice is transformed into a regular square Ising lattice with nearest-neighbor, next-nearest-neighbor, and four-spin interactions, and the critical fixed point is found at K₁=0.5769, K₂=-0.0671, and K₃=0.3428, which determines the critical temperature of the system. It is also found that this system and the regular square Ising lattice, and the eight-vertex model belong to the same universality class.     

压力下碱金属铁硒基超导体中的现象与物理

在凝聚态物理研究中, 压力作为对物质状态调控的独立变量得到了广泛的应用. 压力对发现物质的新现象、新规律及对其形成机理的理解和对相关理论的验证起到了重要的作用, 尤其在超导电性的研究中取得了巨大的成功. 文章简要的介绍了通过利用压力手段对具有相分离结构的碱金属铁硒基超导体A_xFe_2-ySe₂ (A=K, Rb, Tl/Rb)开展的系列研究所取得的实验结果, 以及其他一些文献中报道的在此方面的主要实验与理论研究工作, 包括压力导致的超导再进入现象和其产生的量子临界机理、其特有的反铁磁绝缘体相在该类超导体实现超导电性中的作用、化学负压力对超导电性的影响、构成该类超导体的反铁磁序与其寄居的超晶格的关系等.     

洞态Ar原子K_α和K_β伴线和超伴线的理论计算

基于全相对论多组态Dirac-Fock方法,对L壳层旁观空穴下Ar原子退激衰变辐射K-X射线K_(α1,2)(K→L_(3,2))和K_(β1,3)(K→M_(3,2))的6908条伴线和超伴线跃迁能、跃迁概率进行了系统计算,计算结果与文献已有数据比较具有很好的一致性.通过对(K~(-1)L~(-1),l=0-8)伴线和(K~(-2)L~(-l),l=0-8)超伴线跃迁谱线卷积得了其合成谱,给出了L壳层不同空穴数下K-X射线伴线和超伴线的平均能量和平均跃迁强度.结果表明,退激辐射X射线能量以及能移与L壳层空穴个数呈现明显的线性关系.基于结论,进一步给出了跃迁能移与L壳层空穴个数之间的关系表达式.研究结果可以为解释离子、原子碰撞过程中产生的X射线谱提供重要的理论支持.     

四方和正交以及单斜相K0.5Na0.5NbO3的结构稳定性和电子结构的第一性原理研究

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K_0.5Na_0.5NbO₃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K_0.5Na_0.5NbO₃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     

金属螺旋型碳纳米管的Peierls相变研究

根据描述电子声子相互作用的Fr?hlich哈密顿量,推导出了金属螺旋型碳纳米管(n₁,n₂)的Peierls相变温度的一般表达式,并利用该式计算了(6,3)的Peierls相变温度.结果表明金属螺旋型碳纳米管在远离室温下都不会发生Peierls相变,仍然保持其金属性 关键词： 螺旋型碳纳米管 电子声子相互作用 Peierls相变     

第一性原理研究Mn和Cu掺杂六钛酸钾(K_2Ti_6O_(13))的电子结构和光学性质

六钛酸钾(K_2Ti_6O_(13))是宽带隙半导体光催化材料,只能响应波长较短的紫外光.为了使K_2Ti_6O_(13)对可见光响应,本文采用第一性原理方法,研究过渡金属Mn和Cu掺杂改性后K_2Ti_6O_(13)的电子结构和光学性质.计算结果表明:Mn,Cu掺杂后K_2Ti_6O_(13)禁带中出现了杂质能级,这些杂质能级由O 2p和Ti 3d与Mn 3d或Cu 3d态杂化而成.对于Mn掺杂的K_2Ti_6O_(13),其带隙值变小,位于能带中间的杂质能级可作为电子跃迁的桥梁,从而实现了对可见光的吸收.对于Cu掺杂的K_2Ti_6O_(13),其带隙值虽略有增大,但是若考虑将与价带相连的杂质能级,带隙值将大大减小,且此杂质能级可抑制光生载流子的复合,使得掺杂后K_2Ti_6O_(13)吸收带边红移至可见光区并在可见光范围内吸收强度明显增强.总的而言,Mn,Cu的掺杂实现了钛酸钾对可见光的吸收,同时Cu掺杂的效果要优于Mn掺杂的效果.研究结果对K_2Ti_6O_(13)在光催化领域上的应用具有重要的意义.     

Magnetic properties and critical behavior of quasi-2D layered Cr4Te5 thin film

Quasi-2D layered Cr₄Te₅ thin film has attracted great attention because it possesses the high Curie temperature close to room temperature and relatively large saturation magnetization. However, the magnetic interactions and the nature of magnetic phase transition in the Cr₄Te₅ film have not been explored thoroughly. In this paper, we focused on the critical behavior of its magnetic phase transition through the epitaxial Cr₄Te₅ film fabricated by pulsed laser deposition (PLD). The final critical exponents β = 0.359(2) and γ = 1.54(2) were obtained by linear extrapolation together with Arrott-Noakes equation of state, and their accuracy was confirmed by using the Widom scaling relation and scaling hypothesis. We find that some magnetic disorders exist in the Cr₄Te₅ film system, which is related to Cr₄Te₅ critical behavior why its critical behavior is quite far from any conventional universality class. Furthermore, we also determined that the Cr₄Te₅ film exhibits a quasi-2D long-range magnetic interaction. Finally, the itinerant ferromagnets of Cr₄Te₅ films were confirmed by the Takahashi’s self-consistent renormalization theory of spin fluctuations. Our work provides a new idea for understanding the mechanism of magnetic interactions in similar 2D layered films.     

Li2CO3/K3PO4复合助熔剂对新型Y2O2S：0.09Ti长余辉磷光体发光性能的影响

采用高温还原法合成了一种新型无稀土掺杂Y₂O₂S:0.09Ti长余辉发光材料。基于助熔剂种类对长余辉发光材料特性的重要作用,选择了对余辉衰减初期和后期余辉强度有明显作用的Li₂CO₃和K₃PO₄两种助熔剂,研究了不同配比(以下用x表示,x=Li₂CO₃/(Li₂CO₃+K₃PO₄))的复合助熔剂对Y₂O₂S:0.09Ti磷光体晶体结构和发光性能的作用,以获得具有较好综合发光性能的Y₂O₂S:0.09Ti磷光体。采用PL光谱和余辉测试仪对材料的发光特性进行了表征,用XRD研究了其晶体结构的变化。XRD结果表明,在复合助熔剂范围内(x=0~1.0)均可获得单相性的Y₂O₂S:0.09Ti磷光体。同时发现复合助熔剂比例不同制备的样品中,Y₂O₂S:0.09Ti磷光体晶体择优取向也发生明显的变化,且高比例Li₂CO₃有助于Y₂O₂S:0.09Ti磷光体的晶体形成。复合助熔剂比例x对样品的激发峰与发射谱主峰位置(565nm)基本没有影响;但助熔剂比例x对发射峰强度则有明显影响,随着x增加,该磷光体的发光强度先增后减,在x=0.8时发光强度最大。     

Influence of alkali metal superoxides on structure,electronic,and optical properties of Be_(12)O_(12) nanocage:Density functional theory study

The effect of alkali metal superoxides M_3O(M = Li,Na,K) on the electronic and optical properties of a Be_(12)O_(12) nanocage was studied by density functional theory(DFT) and time-dependent density functional theory(TD-DFT).The energy gaps(Eg) of all configurations were calculated.Generally,the adsorption of alkali metal superoxides on the Be_(12)O_(12) nanocage causes a decrease of Eg.Electric dipole moment μ,polarizability α,and static first hyperpolarizability β were calculated and it was shown that the adsorption of alkali metal superoxides on Be_(12)O_(12) increases its polarizability.It was found that the absorption of M_3 O on Be_(12)O_(12) nanocluster improves its nonlinear optical properties.The highest first hyperpolarizability(β≈ 214000 a.u.) is obtained in the K_3O–Be_(12)O_(12)nanocluster.The TD-DFT calculations were performed to investigate the origin of the first hyperpolarizabilities and it was shown that a higher first hyperpolarizability belongs to the structure that has a lower transition energy.     

VO2金属-绝缘体相变机理的研究进展

VO₂是一种热致相变金属氧化物. 在341 K附近, VO₂发生由低温绝缘体相到高温金属相的可逆转变, 同时伴随着光学、电学和磁学等性质的可逆突变, 这种独特的性质使得VO₂在光电开关材料、智能玻璃、存储介质材料等领域有着广阔的应用前景. 因此, VO₂金属-绝缘体可逆相变一直是人们的研究热点, 但其相变机理至今未有定论. 首先, 简要概述了VO₂相变时晶体结构和能带结构的变化情况: 从晶体结构来讲, 相变前后VO₂从低温时的单斜相VO₂(M)转变为高温稳定的金红石相VO₂(R), 在一定条件下此过程也可能伴随着亚稳态单斜相VO₂(B)与四方相VO₂(A)的产生; 从能带结构来看, VO₂处于低温单斜相时, 其d_//能带和π^*能带之间存在一个禁带, 带宽约为0.7 eV, 费米能级恰好落在禁带之间, 表现出绝缘性, 而在高温金红石相时, 其费米能级落在π^*能带与d_//能带之间的重叠部分, 因此表现出金属导电性. 其次, 着重总结了VO₂相变物理机理的研究现状. 主要包括: 电子关联驱动相变、结构驱动相变以及电子关联和结构共同驱动相变的3种理论体系以及支撑这些理论体系的实验结果. 文献报道争论的焦点在于, VO₂是否是Mott绝缘体以及结构相变与MIT相变是否精确同时发生. 最后, 展望了VO₂材料研究的发展方向.     

K3[Cr(CN)6]中Cr3+电子跃迁几率(I)

本文首先计算了K₃[C_r(CN)₆]中C_r³⁺在外加直流磁场H绕晶体形态轴(a,b,c)情况下能级的分裂,然后计算相应的波函致,最后计算了电子极大受激相对跃迂几率。     

(K3N)n(n=1,…,5)团簇结构与性质的密度泛函理论研究

利用密度泛函理论B3LYP方法,在6-311G*水平上对碱金属氮化物(K₃N)_n(n=1,…,5)团簇各种可能构型进行几何结构优化,预测各团簇的最稳定结构,并对其成键特性、电荷分布、振动特性及稳定性进行分析研究.结果表明,随着n的增大,(K₃N)_n(n=1,…,5)团簇的最稳定结构逐渐由平面结构向空间立体结构转变,(K₃N)₄、(K₃N)₅团簇为类似晶体的层状结构;团簇中N原子的配位数以5、6较多见;团簇中N原子的平均自然电荷为-1.608e,K原子的平均自然电荷为+0.550e,K-N键为较强的离子键;(K₃N)₄团簇有相对较高的动力学稳定性.     

电触发二氧化钒纳米线发生金属-绝缘体转变的机理

二氧化钒(VO_2)是一种强关联相变材料,在341 K下发生金属-绝缘体转变.尽管对于VO_2相变的物理机理进行了大量研究,但科学家仍未形成统一认识.与热致VO_2相变相比,电触发VO_2相变应用前景更为广阔,但其机理也更为复杂.本文利用原位通电杆和超快相机技术,在透射电镜下原位观察了单晶VO_2纳米线通电时的相转变过程,记录了相变过程中对应的电压-电流值,并在毫秒尺度下捕捉到了VO_2的过渡相态.发现VO_2电致相变并非由焦耳热引起,推断其机理是载流子注入.同时观察到电子结构相变和晶体结构相变存在解耦现象,进一步支持了上述推断.将VO_2纳米线两端施加非接触式电场,观察到VO_2纳米线在电场中的极化偏移,而未观察到相变发生,该现象同样支持相变的载流子注入机理.研究表明VO_2的金属-绝缘体转变遵循电子-电子关联机理,即根据电子关联的Mott转变进行.     

Eu3+激活K2CaP2O7荧光粉的制备和发光性质

采用高温固相法制备了系列不同浓度Eu³⁺离子掺杂的K₂CaP₂O₇红色荧光粉。通过X射线衍射、扫描电子显微镜、荧光光谱和荧光寿命曲线等手段对荧光粉的物相结构、形貌以及发光性质进行了研究。结果表明所制备的荧光粉均属于单斜结构,Eu³⁺离子掺杂没有引起晶体结构明显变化,荧光粉形貌不规则,颗粒为微米量级且部分发生团聚。在393 nm紫外光激发下,荧光粉显示出红光发射,最强发射峰位于613 nm。Eu³⁺离子掺杂浓度对发光强度有显著影响,最佳掺杂摩尔分数为0.08,由此计算能量传递临界距离为1.61 nm。荧光寿命受掺杂浓度影响较小,当Eu³⁺掺杂摩尔分数为0.005~0.10时,荧光寿命在2.45~2.58 ms范围内。变温发射光谱显示,测试温度为150℃时,荧光粉的发光强度为室温的73%。研究表明,Eu³⁺离子掺杂的K₂CaP₂O₇是性能较好的红色荧光粉。     

Infrared study of the reactivity of CO with K2 and K3 molecules isolated in solid argon

Cocondensation of K atoms and CO molecules with an excess of argon onto a cold substrate (10 K) leads to the formation of strongly perturbed CO complexes from ground state partners only when a large proportion of K clusters is present. It is established that ground state, isolated K atoms do not react with carbon monoxide as do small potassium clusters. K₂CO, K₃CO and K₂(CO)₂ species are identified by CO stretching motions and are unambiguously characterized using systematic concentration and isotopic studies (¹²C, ¹³C and ¹⁸O) as well as triple doping K/CO/O₂/Ar experiments. K₂(CO)₂ is a very labile species which seems likely to have a C_2v doubly bridged structure. It rearranges into the well known acetylene diolate K … O-CC-O … K species upon exposure to infrared light (0.3–0.45 eV).     

Fe-Pb合金凝固多相体系内偏析形成过程的三维数值模拟

基于Eulerian-Eulerian方法和流体体积技术,建立了三维多相流体动力学凝固模型,并将其与质量、动量、溶质和热焓守恒方程相耦合,对Fe-Pb合金侧向凝固过程进行了数值模拟.首先,分析了分布面积二次梯度((SPb))和浓度二次梯度((CPb))对偏析模式的影响,结果表明:液、气两相的流动相变使偏析模式表现为上端X形下端V形,X偏析由气相相变驱动力和多取向相变作用下的"散射"形成;ttc时,随(SPb)和(CPb)曲线降低,X偏析的下偏析角增大,上偏析角和V偏析角减小,Pb收得率增大,有利于获得含量稳定弥散的凝固组织.此外,还研究了液、气两相交互流动下通道偏析的形成机理,结果表明:通道偏析仅存在于流动-相变交互作用(ul·cl和ug·cg)为负值的区域,该区域的流动扰动抑制合金的局部凝固,促进偏析通道生长;流动-相变交互作用负值越小,偏析通道持续增长越稳定.模拟结果与实验结果相符合,验证了模型的准确性.     

Kinetic Behaviors of a Competitive Population and Fitness System in Exchange-Driven Growth

We proposed an aggregation model of two species aggregates of fitness and population to study the interaction between the two species in their exchange-driven processes of the same species by introducing the monomer birth of fitness catalyzed by the population, where the fitness aggregates perform self-death process and the population aggregates perform self-birth process. The kinetic behaviors of the aggregate size distributions of the fitness and population were analyzed by the rate equation approach with their exchange rate kernel K₁(k,j)=K₁kj and K₂(k,j)=K₂kj, the fitness aggregate's self-death rate kernel J₁(k)=J₁k, population aggregate's self-birth rate kernel J₂(k)=J₂k and population-catalyzed fitness birth rate kernel I(k,j)=Ikj^u. The kinetic behavior of the fitness was found depending crucially on the parameter u, which reflects the dependence of the population-catalyzed fitness birth rate on the size of the catalyst (population) aggregate. (i) In the u ≤0 case, the effect of catalyzed-birth of fitness is rather weak and the exchange-driven aggregation and self-death of the fitness dominate the process, and the fitness aggregate size distribution a_k(t) does not have scale form. (ii) When u>0, the effect of the population-catalyzed birth of fitness gets strong enough, and the catalyzed-birth and self-death of the fitness aggregates, together with the self-birth of the population aggregates dominate the evolution process of the fitness aggregates. The aggregate size distribution a_k(t) approaches a generalized scaling form.     

水热体系TeO2-K3PO4-H2O中一个新化合物——K2Te4O9·3H2O的合成与结晶

作者用水热法对TeO₂-K₃PO₄-H₂O体系作了初步的合成与结晶尝试。在给定的条件和组成范围内除了能形成TeO₂晶体外,还能生成一种点阵参数为a=b=10.734?,c=21.041?,α=β=90°,γ=120°的三方晶系的化合物γ,其分子式为K₂Te₄O₉·3H₂O。结晶区的产物主要取决于原料的k=TeO₂/K₃PO₄(克分子比:当k≤1.9时,仅生成γ晶体;k≥2.22时,单独生成TeO₂晶体;而当1.92晶体出现,本文还给出了γ晶相的DTA曲线和X射线粉末衍射谱线的相对强度与相应面间距的详细数据。 关键词：     

Liquid–liquid phase transition and anomalous diffusion in simulated liquid GeO2

We perform molecular dynamics (MD) simulation of diffusion in liquid GeO₂ at the temperatures ranged from 3000 to 5000 K and densities ranged from 3.65 to 7.90 g/cm³. Simulations were done in a model containing 3000 particles with the new interatomic potentials for liquid and amorphous GeO₂, which have weak Coulomb interaction and Morse-type short-range interaction. We found a liquid–liquid phase transition in simulated liquid GeO₂ from a tetrahedral to an octahedral network structure upon compression. Moreover, such phase transition accompanied with an anomalous diffusion of particles in liquid GeO₂ that the diffusion constant of both Ge and O particles strongly increases with increasing density (e.g. with increasing pressure) and it shows a maximum at the density around 4.95 g/cm³. The possible relation between anomalous diffusion of particles and structural phase transition in the system has been discussed.