基于ZnTe1-xYx（Y=O,S,Se）中间带光伏材料光电性能的第一性原理研究

采用基于密度泛函理论框架下的第一性原理方法计算了高失配三元合金ZnTe1-xYx(Y=O,S,Se)的能带结构、电子特性与光学性能。通过对半导体态密度的计算证实了在闪锌矿结构的ZnTe中掺杂O、S或Se原子可能得到独立的中间带结构,该结构可提高光伏材料对能量低于母体半导体带隙光子的吸收效率。研究结果表明,中间带在ZnTe1-xOx中是由掺杂的O原子的2p态与处于导带的Zn原子的4s态耦合而成,符合能带反交叉模型。另外,与ZnTe1-xSx和ZnTe1-xSex相比,随着掺杂O浓度的变化,ZnTe1-xOx的中间带表现出较高的稳定性主要是因为O与Te之间存在最大的电负性差。     

AZrX3(A=Ba,Ca; X=S,Se, Te)钙钛矿结构及光电特性的第一性原理研究

基于密度泛函理论的第一性原理计算方法,考虑自旋轨道耦合(SOC)效应,采用Heyd-Scuseria-Ernzerhof (HSE06)杂化泛函对带隙进行修正,系统研究了AZrX₃(A=Ba, Ca; X=S, Se, Te)无铅钙钛矿的晶体结构、电子结构和光学性质。结果表明,AZrX₃钙钛矿为直接带隙半导体材料,且材料的容忍因子介于0.85～0.95之间、形成能位于-1.09～-1.83 eV/atom之间、分解能介于-0.09～0.06 eV/atom之间,表明AZrX₃钙钛矿具有稳定的结构。其中,BaZrS₃具有空穴有效质量小(0.21 m₀)、载流子迁移率高、可见光吸收范围宽、光吸收系数高(～4×10⁵cm^-1)等特点,且光谱极限最大效率(SLME)可达32.36%,高于CH₃NH₃PbI₃(～30%),是很有前途的太阳电池材料。AZrSe₃     

La2O2S电子结构及光学性质的第一原理研究

基于密度泛函理论的第一原理方法研究了La2O2S的电子结构及光学性质.能带结构分析表明:L2O2S是一种间接带隙的半导体材料,价带顶和导带底分别位于A点和K点.对带隙剪刀修正后,也通过第一原理方法研究了La2O2S的光学性质.计算并分析了La2O2S介电函数的虚部、实部以及由它们所派生的光学常数,即折射率、消光系数、反射率、吸收系数和透光率等.     

S和Al掺杂单层g-C3N4电子结构与光学性质的第一性原理研究

g-C₃N₄是一种典型的聚合物半导体材料,在可见光下就能完成对半导体要求较高的光催化反应。采用基于密度泛函理论的第一性原理平面波超软赝势方法研究了单层g-C₃N₄、S单掺g-C₃N₄、Al单掺g-C₃N₄和S-Al共掺g-C₃N₄的形成能、电子结构及光学性质。结果表明：S掺杂空隙I位置、Al掺杂N2位置时,杂质原子最易掺入g-C₃N₄体系。与单层g-C₃N₄相比,掺杂后的体系均发生了晶格畸变以及红移现象,拓展了体系的光吸收范围,可推测出S、Al掺杂能够提高g-C₃N₄体系的光催化性。其中,S-Al共掺杂体系的光催化性是最优的,原因是共掺杂体系的分子轨道有较强的离域性,有利于提高载流子的迁移率,并且共掺杂能使单掺杂引入的深能级变浅,减少杂质能...     

Co2MnSi1-xZx(Z=B,P, As) Heusler合金的磁性和电子结构的第一性原理计算

通过第一性原理计算研究了Co₂MnSi_1-xZ_x(Z=B, P, As) Heusler合金的能带结构和自旋极化,同时也证明了具有不同价电子的其他元素Z对Si的取代可以控制费米能级在带隙中的移动。与此同时,随着同种Z元素浓度的变化,晶格参数具有接近线性变化的特征,并且这些合金的能带结构具有相似的特点。不同合金的磁矩随价电子数呈线性变化趋势,符合Slater-Pauling行为。由计算结果可知,当x=0.125左右,Co₂MnSi_1-xP_x和Co₂MnSi_1-xAs_x合金具有较好的电子性质和较高的自旋极化。     

单层WxMo1-xS2合金电子和光学性质的第一性原理研究

采用基于密度泛函理论(DFT)的第一性原理方法对WxMo1-xS2(x=0,0.25,0.5,0.75,1)单层合金的电子结构和光学性质进行了较为系统的研究.计算结果表明:合金的带隙都为直接带隙,随着W含量增加可由1.802 eV增加至1.940 eV,但并不是线性增加.电荷差分密度图计算结果显示,随着W含量的增加,Mo原子失电子数逐渐增加,W原子得电子数逐渐增加.合金的光学性质可随着W含量的变化调谐.随着W含量的增加,WxMo1-xS2合金的静态介电常数逐渐减小,虚部吸收阈值逐渐增大,吸收边向高能区移动.与本征Mo16S32相比,WxMo1-xS2合金在紫外光区域(6～8.5 eV)表现出更强的紫外吸收能力,而W12Mo4S32和W16S32合金在可见光区域(～3 eV)有着更高的吸收系数,这在理论上表明此类单层合金在可见光及近紫外光区域可应用于光电信号的探测.     

第一性原理计算XCO3（X=Ca、Mg）的热力学性质

采用第一性原理(First-principles)的超软赝势平面波法,结合广义梯度近似(GGA)及PW91算法,计算了煤中的方解石CaCO3、菱镁矿MgCO3和白云石CaMg(CO3)2的电子结构和热力学性质。首先,分别对这3种矿物质的结构进行优化,使其达到最稳定的状态,计算结果给出了这3种矿物质的电子结构和晶胞参数。其次,采用声子谱态密度方法计算了这3种矿物质的熵S、热容Cp、焓H及吉布斯自由能G。最后,由相应的数据拟合成图像。这样,采用微观计算得出的结果,给煤灰结渣问题的研究提供理论上的指导作用。     

Pt-M(M=Fe, Co, Ni)金属间化合物电子结构和弹性性质的第一性原理研究

通过基于密度泛函理论的第一性原理计算方法,研究了Pt-M(M=Fe,Co,Ni)各金属间化合物的结构、能量、电子结构和弹性性质。首先对Pt-M(M=Fe,Co,Ni)金属间化合物进行几何优化,对其能带结构、总态密度、分态密度、键合特征和弹性性质进行研究,并计算各金属间化合物的结合能与生成焓。计算所得晶格参数与实验值和文献计算值吻合。PtFe_3的生成焓最小,结合能最大,说明PtFe_3较其他合金相更稳定、键合力更强。通过对Pt-M(M=Fe,Co,Ni)的能带结构和电子态密度进行计算,分析了其结构稳定性的物理本质。PtFe_3-t中Pt-Fe和Fe-Fe键相比其他合金相键长较短且电荷密度较高,说明PtFe_3-t中Pt-Fe和Fe-Fe键的键能比其他合金相大,所以PtFe_3-t合金相的结构稳定性最好。对Pt-M(M=Fe,Co,Ni)弹性性质的研究表明PtFe_3为脆性相,PtFe、Pt3Fe、PtCo、Pt_3Co、PtNi和PtNi3为延性相,其中Pt_3Co的塑性最好,PtFe_3-t有较高的弹性模量,其原子间结合力相对较强,材料的强度较大。     

Sn掺杂钙钛矿BaTiO3电子结构的第一原理研究：Ba（SnxTi1-x）O3

采用基于密度泛函理论（DFT）的全势线性缀加平面波（FPLAPW）方法,对Sn掺杂钙钛矿BaTiO3电子结构进行了第一性原理研究,构造了3个不同的超胞,分别为1×2×2、1×1×3和1×1×2,即：分别由4个、3个和2个单胞组成的超胞。研究表明：当X≤0．33时,随着X值的增大,相应的费米面会向Sn掺杂BaTiO3导带的更高的能量处移动,以适应掺杂电子数目的增多,其态密度的演化可以用一个严格的带状模型来描述,所以,掺入BaTiO3体系的每一个电子都对体系的导电过程有贡献,从而使其室温介电常数大幅度提高,介电损失相对减小。复合材料的态密度的重新分布主要是由O—P与所掺入的Sn混合后的杂化而引起的。     

Ti掺杂β-Ga2O3电子结构和光学性质的第一性原理计算

采用基于密度泛函理论框架下的第一性原理计算方法,研究了Ti 掺杂β-Ga₂O₃系统的电子结构和光学性质。计算结果表明,Ti 替代八面体的Ga(2)时系统形成能最低,容易在实验上合成;Ti掺杂在导带底附近引入了浅施主能级,极大地提高了β-Ga₂O₃系统的导电性。Ti 掺杂时稳定体系倾向于自旋极化态,且费米面处自旋极化率接近100%。光学性质的计算结果显示,Ti 掺杂β-Ga₂O₃是极具潜力的n型紫外透明的半导体。     

四面体掺杂尖晶石结构Co1-xRexCr2O4(Re=Li、Na、K、Rb)的电子结构和光学性质

采用基于密度泛函理论(DFT)的平面波超软赝势方法, 计算了CoCr₂O₄及Li、Na、K和Rb四面体掺杂CoCr₂O₄的基态结构、电子结构和光学性质。计算结果表明: 一价离子四面体掺杂都导致晶格有微小的畸变, 使体系的稳定性降低, Rb掺杂的体系最稳定; 电子态密度的计算结果表明: 掺杂体系的导带主要有Co-3d和Cr-3d轨道电子构成, 掺杂离子改变了CoCr₂O₄导带的电子结构, 主要引起了导带Co-3d态密度峰的下移, 随着掺杂浓度的增大, 费米能级进入价带更深; 光学性质计算表明: 掺杂体系的吸收光谱发生红移, 并在低能区有很强的吸收, 表明掺杂能极大地提高CoCr₂O₄对可见光的吸收和光催化效率。     

Electronic band-edge properties of rock salt PbY and SnY (Y= S, Se, and Te)

The electronic band-edges of lead chalcogenides PbY and tin chalcogenides SnY (where Y = S, Se, and Te) are investigated by the means of a full-potential linearized augmented plane wave (FPLAPW) method and the local density approximation (LDA). All six chalcogenide binaries have similar electronic structures and density-of-states, but there are differences in the symmetry of the band-edge states at and near the Brillouin zone L-point. These differences give the characteristic composition, pressure, and temperature dependences of the energy gap in Pb_1−xSn_xY alloys.We find that: (1) SnY are zero-gap semiconductors E_g = 0 if the spin–orbit (SO) interaction is excluded. The reason for this is that the conduction band (CB) and the valence band (VB) cross along the Q ≡ LW line. (2) Including the SO interaction splits this crossing and creates a direct gap along the Q-line, thus away from the L symmetry point. Hence, the fundamental band gap E_g in SnY is induced by the SO interaction and the energy gap is rather small E_g ≈ 0.2–0.3 eV. At the L-point, the CB state has symmetric and the VB state is antisymmetric thereby the L-point pressure coefficient ∂E_g(L)/∂p is a positive quantity. (3) PbY have a direct band gap at the L-point both when SO coupling is excluded and included. In contrast to SnY, the SO interaction decreases the gap energy in PbY. (4) Including the SO interaction, the LDA yields incorrect symmetries of the band-edge states at the L-point; the CB state has and the VB state has symmetry. However, a small increase of the cell volume corrects this LDA failure, producing an antisymmetric CB state and a symmetric VB state, and thereby also yields the characteristic negative pressure coefficient ∂E_g(L)/∂p in agreement with experimental findings. (5) Although PbY and SnY have different band-edge physics at their respective equilibrium lattice constants, the change of the band-edges with respect to cell volume is qualitatively the same for all six chalcogenides. (6) Finally, in the discussion of the symmetry of the band edges, it is important to clearly state the chosen unit cell origin; a shift by (a/2,0,0) changes the labeling of the irreducible representations.     

Theoretical study of the gap evolution of In2X3 (X=O, S, Se, Te) with lattice compression

We report a systematic study of the electronic structure of In₂X₃ (X=O, S, Se, Te) semi-conductors using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method. Taking into account the experimental structure of each compound we have determined the gap evolution under lattice compression in the whole series. We have found that the compression of the lattice produces an enhancement of the energy gap. This could be driven in some cases by doping with shallow impurities.     

CoxR1-xAl2O4(R=Zn,Mg)钴蓝颜料反射性能的研究

采用化学共沉淀法成功地制备出适用于彩电显象管内荧光体着色的Ｃｏ_ｘＲ_１－ｘＡｌ_２Ｏ_４（Ｒ＝Ｚｎ、 Ｍｇ, ｘ＝０．８～１．０）钴蓝颜料： ４５０ｎｍ波长处反射率最大提高１８．２％, ６００ｎｍ处反射率最大降低５％。通过对该颜料反射率的影响因素,如掺杂离子类型、掺杂浓度和Ｃｏ^２＋离子浓度的探讨,结论如下：Ｚｎ^２＋、Ｍｇ^２＋改变钴蓝颜料反射性能的作用机理为晶格畸变引起Ｃｏ^２＋３ｄ轨道电子能级分裂程度的变化;对于掺杂离子Ｚｎ^２＋、Ｍｇ^２＋,ｘ下限值分别约为０．８５和０．８．     

Phase separation during the melting of oxide borates LnCa4O(BO3)3 (Ln=Y, Gd)

GdCa₄O(BO₃)₃ (GdCOB) and YCa₄O(BO₃)₃ (YCOB) single crystals have been grown from the melt by the Czochralski method. Subsequent DTA analysis of the single crystals showed different behavior for both substances. During the first heating both crystals showed a single sharp melting peak at 1490°C (GdCOB) or at 1504°C (YCOB), respectively. In subsequent heating/cooling runs only GdCOB shows one single peak, whereas YCOB shows five peaks. Moreover, phase separation of the melt can be observed by optical observation and by EDX measurements. This behavior can be explained by a miscibility gap in the YCOB melt. The YCOB crystal is formed from the stoichiometric melt by a monotectic reaction.     

First principles calculations of the electronic, dynamical, and thermodynamic properties of the rocksalt ScX (X = N, P, As, Sb)

We have investigated the electronic, dynamical, and thermodynamic properties of the rocksalt ScX (X = N, P, As, Sb) using a plane-wave pseudopotential method within the generalized gradient approximation in the frame of density functional perturbation theory. The calculated lattice constants are found to differ by less than 0.56% from the available experimental values. These materials have the indirect Γ–X band gaps and a wide and direct band gap at the X-point in band structure, which are closer to experimental results than the previous calculations. A linear-response approach is used to calculate the phonon frequencies, the phonon density of states and LO–TO splitting. The obtained phonon frequencies at the zone-center (Γ-point) for the Raman-active and infrared-active modes are analyzed. We also calculate the thermodynamic functions using the phonon density of states, and the calculated values are in nearly perfect agreement with experimental data.     

Recent Progress in the Design of Advanced Cathode Materials and Battery Models for High‐Performance Lithium‐X (X = O2, S,Se, Te,I2, Br2) Batteries

Recent advances and achievements in emerging Li‐X (X = O₂, S, Se, Te, I₂, Br₂) batteries with promising cathode materials open up new opportunities for the development of high‐performance lithium‐ion battery alternatives. In this review, we focus on an overview of recent important progress in the design of advanced cathode materials and battery models for developing high‐performance Li‐X (X = O₂, S, Se, Te, I₂, Br₂) batteries. We start with a brief introduction to explain why Li‐X batteries are important for future renewable energy devices. Then, we summarize the existing drawbacks, major progress and emerging challenges in the development of cathode materials for Li‐O₂ (S) batteries. In terms of the emerging Li‐X (Se, Te, I₂, Br₂) batteries, we systematically summarize their advantages/disadvantages and recent progress. Specifically, we review the electrochemical performance of Li‐Se (Te) batteries using carbonate‐/ether‐based electrolytes, made with different electrode fabrication techniques, and of Li‐I₂ (Br₂) batteries with various cell designs (e.g., dual electrolyte, all‐organic electrolyte, with/without cathode‐flow mode, and fuel cell/solar cell integration). Finally, the perspective on and challenges for the development of cathode materials for the promising Li‐X (X = O₂, S, Se, Te, I₂, Br₂) batteries is presented.     

Electronic band structure calculations on thin films of the L21 full Heusler alloys X2YSi (X, Y = Mn, Fe, and Co): Toward spintronic materials

To design half-metallic materials in thin film form for spintronic devices, the electronic structures of full Heusler alloys (Mn₂FeSi, Fe₂MnSi, Fe₂FeSi, Fe₂CoSi, and Co₂FeSi) with an L2₁ structure have been investigated using density functional theory calculations with Gaussian-type functions in a periodic boundary condition. Considering the metal composition, layer thickness, and orbital symmetries, a 5-layered Co₂FeSi thin film, whose surface consists of a Si layer, was found to have stable half-metallic nature with a band gap of ca. 0.6 eV in the minority spin state. Using the group theory, the difference between electronic structures in bulk and thin film conditions was discussed.