Al-15wt.%Mg2Si复合材料中二元相的研究

原位内生法制备Al-15wt%Mg₂Si复合材料,其中二元相成分的研究很少,本文通过XRD测试方法,定性和定量的分析材料中的相成分和相含量。利用Reflex模拟Al-Mg-Si系合金的XRD衍射图谱,并与XRD测试结果对比。利用CASTEP中基于密度泛函理论的第一性原理方法,对Al-Mg₂Si复合材料中的Mg₂Si相和Mg₁₇Al₁₂相的平衡晶格常数,热力学参数和弹性性质做了系统的研究,分析两相的稳定性和力学性能。XRD分析结果显示,Al-15wt%Mg₂Si复合材料中仅含有α-Al相和Mg₂Si相,且Mg₂Si相的质量分数为14.9wt.%。模拟与实验中,相同晶面指数的XRD标定值相差很小,实验值验证了模拟值的可靠性。模拟值证实Al-Mg₂Si复合材料中,理论上只形成α-Al相和Mg₂Si相。CASTEP计算结果表明,Al-Mg₂Si复合材料中的Mg₂Si相较Mg₁₇Al₁₂相易于形成,且稳定性较好。Mg₂Si相的弹性模量E,剪切模量G,体模量B均大于Mg₁₇Al₁₂相,Mg₂Si相的力学性能较好,但脆性较大,且塑性较差。     

Can We Predict the Isosymmetric Phase Transition? Application of DFT Calculations to Study the Pressure Induced Transformation of Chlorothiazide

Isosymmetric structural phase transition (IPT, type 0), in which there are no changes in the occupation of Wyckoff positions, the number of atoms in the unit cell, and the space group symmetry, is relatively uncommon. Chlorothiazide, a diuretic agent with a secondary function as an antihypertensive, has been proven to undergo pressure-induced IPT of Form I to Form II at 4.2 GPa. For that reason, it has been chosen as a model compound in this study to determine if IPT can be predicted in silico using periodic DFT calculations. The transformation of Form II into Form I, occurring under decompression, was observed in geometry optimization calculations. However, the reverse transition was not detected, although the calculated differences in the DFT energies and thermodynamic parameters indicated that Form II should be more stable at increased pressure. Finally, the IPT was successfully simulated using ab initio molecular dynamics calculations.     

太阳能电池钙钛矿材料模拟计算研究

为了提高钙钛矿(ABX₃)晶体结构稳定性及其光电转换效率,采用第一性原理计算和CASTEP计算程序研究了CsPbI₃的3种同质异构体和B位、X位掺杂对材料结构稳定性和能带结构的影响。结果表明,3种同质异构体的结构稳定性依次为单斜结构、斜方结构、立方相结构,其中斜方相带隙为2.535 eV; X位掺杂时,F掺杂能大幅度提高带隙,CsPbI₃-F带隙值为2.659 eV,Br掺杂的CsPbI₃-Br带隙值为1.7 eV; B位掺杂可以有效提高立方相稳定性,其中Ca掺杂结构的结合能降低最为明显。     

利用光致发光法测定AlxGa1-xN外延膜中的铝元素含量

采用深紫外光致发光技术测量AlxGa1-xN半导体异质外延膜的禁带宽度,结合Material Studio软件中的CASTEP模块模拟计算AlxGa1-xN异质外延膜材料的弯曲因子,测定了AlxGa1-xN外延膜样品中的Al元素物质的量分数。结果表明,发射波长为224.3nm的HeAg激光器能够激发AlxGa1-xN半导体材料产生发光现象。CASTEP软件模拟计算得到AlxGa1-xN的弯曲因子为1.01462±0.06772eV,认为其弯曲因子在1.0eV附近,由此可以理论计算得到具有Al组分梯度的一系列AlxGa1-xN外延膜样品中的Al元素物质的量分数。     

First-principles study on electronic structure and absorption spectra for the CaWO4 crystal with oxygen vacancy

The electronic structure and absorption spectra for the perfect CaWO₄ and the CaWO₄ containing oxygen vacancy have been calculated using density functional theory code CASTEP with the lattice structure being optimized. The results indicate that the CaWO₄ crystal containing , an additional absorption spectrum in the region of visible light. And the absorption spectrum can be fit into two Gaussian-shape absorption spectra with peaks at 360 and 415 nm. These peaks are located at the experimentally observed position. It is predicted that the 340 and the 420 nm absorption spectra are related to the existence of in the CaWO₄ crystal.     

阴离子对磷灰石和白云石表面性质影响的第一性原理研究

结合密度泛函理论（DFT）计算,研究磷矿反浮选脱镁过程中,三种主要阴离子（油酸根离子、SO42-和H2PO4-）在氟磷灰石和白云石吸附特性的差异。结果显示,油酸根离子、SO42-和H2PO4-均能在氟磷灰石和白云石表面发生化学吸附。氟磷灰石表面暴露的Ca原子位于磷酸根之上,表面Ca原子活性强,SO42-和H2PO4-在Ca位点的吸附能分别为-818.74~-1058.30 kJ/mol和-572.78~-709.02 kJ/mol。白云石表面暴露Ca、Mg和O原子,但O原子活性较强,不利于阴离子在白云石表面的吸附,SO42-和H2PO4-在白云石表面Ca\Mg位点的吸附能分别为-135.92 kJ/mol \ -156.30 kJ/mol和-127.03 kJ/mol \ 146.95 kJ/mol。因此,SO42-和H2PO4-更容易吸附在氟磷灰石表面形成不溶性钙盐,屏蔽了氟磷灰石表面的活性位点,导致磷灰石被抑制;白云石表面Ca、Mg原子位点密度大于氟磷灰石,存在更多的吸附位点与捕收剂结合。     

Ca^2＋在金红石型二氧化钛晶体（110）晶面沉积过程原理

基于密度泛函理论(DFT)框架下的第一性原理平面波超软赝势方法,采用CASTEP程序,结合结构优化方法,研究了液中Ca2+在金红石型TiO2(110)晶面的沉积过程.结果表明,在沉积过程中,溶液中的Ca2+首先和水分子结合形成络合物[Ca(H2O)5]2+,而沉积的一个关键条件为TiO2(110)晶面的羟基化.[Ca(H2O)5]2+与羟基化的TiO2(110)晶面通过静电作用相互结合完成Ca2+的沉积.     

Experiment and simulation of infrared emissivity properties of doped LaAlO3

In this study, LaAlO₃ doped with Sr/Co/Mn was prepared by sol-gel method, with its infrared (IR) radiative properties and variation mechanism investigated by X-ray powder diffraction, X-ray photoelectron spectroscopy, IR, scanning electron microscopy. Meanwhile, the electronic band structure was simulated by Cambridge Serial Total Energy Package. The conclusions are as follows: the order of emissivity in the near-IR band is La_0.67Sr_0.33Al_0.67Mn_0.33O₃> La_0.67Sr_0.33Al_0.67Co_0.33O₃> LaAl_0.67Mn_0.33O₃> LaAl_0.67Co_0.33O₃> LaAlO₃. In 0–2.5 μm at room temperature, the emissivity of La_0.67Sr_0.33Al_0.67Mn_0.33O₃ can reach 0.9504. The emissivity increase mechanism lies in the further free carrier absorption caused by numerous small polarons formed by the Sr-Mn co-doping and increased concentration of electron-oxygen vacancies. Meanwhile, the Sr-Mn co-doping causes lattice distortion and strengthens the lattice vibration absorption. The band gap of La_0.67Sr_0.33Al_0.67Mn_0.33O₃ is 0.910 eV, much smaller than 3.445 eV of LaAlO₃, favorable to the valence band electron transition, generating more electron-oxygen vacancy pairs and promoting free carrier absorption. La_0.67Sr_0.33Al_0.67Mn_0.33O₃ conduction band migrates to the lower energy region, while Mn3d impurity energy level appears. Thanks to the band gap reduction, dielectric function imaginary peaks, and absorption coefficient peaks are red-shifted. Due to its high emissivity, La_0.67Sr_0.33Al_0.67Mn_0.33O₃ has a high utilization value and broad potential application.     

Structure and properties of aluminosilicate garnets and katoite: an ab initio study

The structural properties of end-members of the aluminosilicate garnet family (pyrope, grossular, spessartine and almandine) and of one hydrogarnet (katoite) have been investigated as a function of applied pressure. The calculated static geometry, bulk modulus and its pressure derivative are in good agreement with available experimental data. The results of a systematic study of the effect of the size of the divalent cation on compressibility are presented. The bonding and dynamics of Mg in pyrope are investigated by using frozen phonon calculations.