Zn2SnO4纳米线高压下的相变研究

 利用金刚石对顶压砧（DAC）对具有反尖晶石结构的透明导体氧化物Zn₂SnO₄（ZTO）纳米线进行了原位高压同步辐射角散X射线衍射（ADXRD）研究。结果发现：在压力为12.9 GPa附近,晶体的对称性降低,并发生晶体结构相变,产生中间过渡相;当压力为32.7 GPa时,发生高压相变,形成高压相。在样品加压前后,纳米线的形貌发生了很大的变化。通过Birch-Murnaghan方程,拟合得到B′₀=4时的体弹模量B₀ =(168.6±9.7) GPa。     

Ca2CuO3的高压结构性质研究

 采用金刚石压砧高压装置（DAC）,对具有Cu—O链结构的Ca₂CuO₃的多晶粉末样品进行了高压同步辐射能散X射线衍射实验。实验结果表明,在0～34 GPa压力范围内,Ca₂CuO₃晶体没有发生结构相变,用Birch-Murnaghan状态方程拟合,得到在压力导数B′₀=4时,零压体弹模量B₀=165.4±1.8 GPa。     

KH2PO4和(CH3NHCH2COOH)CaCl2在高压下的状态方程与相变

 在活塞圆筒式p-V关系测量装置上，研究了KH₂PO₄（KDP）和(CH₃NHCH₂COOH)CaCl₂［Tris-sarcosine calcium chloride（TSCC）］在室温下、4.5 GPa内的p-V关系。实验结果表明：KDP在2.1 GPa左右有一个相变；TSCC在0.8 GPa和3.2 GPa左右各有一个相变。本工作还给出了它们在相变前后的状态方程，以及它们的格临爱森参数γ₀、体积模量B₀和B₀的压力导数B₀'。     

Cd1-xZnxTe在高压下的电学性质、状态方程与相变

 在金刚石压砧装置上,采用电阻和电容测量方法研究了Cd_1-xZn_xTe（x=0.04）在室温下、17 GPa内的电阻、电容与压力的关系。实验结果表明,它在3.1 GPa左右和5 GPa左右发生了两次电子结构相变,而在3.1 GPa以上和5.7 GPa左右发生了两次晶体结构相变。同时,还在活塞-圆筒测量装置上研究了Cd_1-xZn_xTe（x=0.04）在室温下、4.5 GPa内的p-V关系。实验结果表明它在3.8 GPa左右发生了相变。本工作还给出了它在相变前后的状态方程,以及它的Grüneisen参数γ₀、体弹模量B₀ 与B₀ 的压力导数B₀′。     

BaCuO2.5在高压下的状态方程与电学性质

 在活塞-圆筒式高压装置上研究了BaCuO_2.5在4.5 GPa内的p-V关系,给出了其状态方程、Grüneisen参数γ₀、零压体弹模量B₀以及B₀的压力导数B′₀。并在金刚石压砧装置（DAC）上测量了样品的电阻、电容随压力变化的关系,结果表明在0~20 GPa内没有发生相变。     

高温高压下B4C合成金刚石的研究

 压力为5.7~6.0 GPa及1 370~1 500 ℃温度范围内，B₄C在Ni₇₀Mn₂₅Co₅系统中，高压相变为金刚石。合成的金刚石为深黑色，含硼量大于1wt%。粒度为20 μm左右，晶形多为立方体与八面体的各种聚形。反应后的金属触媒中，存在Ni₂B等硼化物；非金属残留物中，存在B₁₃C₂等高硼碳化物。     

CuO在高压下的状态方程、电学性质与相变

 在活塞－圆筒式高压装置上研究了CuO在4.5 GPa内的p-V关系，给出了它的状态方程、格临爱森参数γ₀、体积模量B₀以及B₀的压力导数B₀'。在金刚石压砧装置上，采用我们建立的电阻、电容测量方法研究了CuO在22 GPa内电阻、电容与压力的关系。实验结果表明，CuO的电阻和电容在一些压力下都发生了突然的变化。这些变化可能与CuO内部的电子结构和晶界处的结构状态变化有关。     

C60高压X射线衍射研究

 采用同步辐射X光源和能量色散法对高纯C₆₀粉末样品进行高压原位X光衍射实验。由金刚石对顶压砧高压装置（DAC）产生高压,用已知状态方程的Pt粉末作内标,由Pt的衍射数据确定样品压力,最高压力达30 GPa。实验结果表明：室温常压下原始C₆₀样品为面心立方结构,晶格常数a=1.420 86 nm。高压下C₆₀的结构有所变化：从p=13.7 GPa开始,(311)线发生劈裂,形成低对称相;随着压力增加,衍射线逐渐变宽,强度逐渐变弱,压力超过25 GPa,衍射背底隆起,C₆₀开始转化成非晶相;在30 GPa左右,衍射线条完全消失,标志着向非晶相转化过程的完成。人们也对C₆₀样品不同压力的高压“淬火”相进行了X光衍射实验。采用非静水压的装样方式,最高压力达44 GPa,结果在30 GPa以上,C₆₀也转变为非晶相。最后我们对C₆₀晶体的压致非晶化现象进行了初步的讨论。     

NiO的高压结构和等温状态方程研究

 运用金刚石对顶砧（Diamond Anvil Cell,DAC）技术,以液氩作为传压介质,在最高压力为67 GPa的压力范围内对NiO进行了原位的同步辐射X射线衍射研究。在整个实验过程中,并未发现第一类结构相变,也没有发现T.Sasaki等预测的在60 GPa左右轴比c/a随压力的变化率而突然增大的现象,且此压力范围内NiO的结构畸变程度随压力的变化趋势相比以前的研究结果要平缓一些。用三阶的Brich-Murnaghan方程对实验数据进行拟合,得到的体弹模量及其对压力的一阶导数分别为B₀=195(4) GPa和B₀′=5.3(2)。     

室温下压致铁钴镍合金的bcc→hcp相变

 本文采用高压X光衍射方法在金刚石对顶压砧中在位地（in situ）研究了Fe₆₈Co₂₄Ni₈（wt%）合金在室温下的压致bcc→hcp结构相变和直到40.5 GPa的等温压缩行为。实验结果表明该合金在常压下为bcc结构，晶格常数a₀=(0.287 0±0.000 1) nm，体积V₀=(7.119±0.007) cm³/mol，密度ρ₀=(7.981±0.008) g/cm³；在20.9 GPa附近出现bcc→hcp结构相变，两相共存压力区约10 GPa，在此区域内有晶面间距d(002)_hcp=d(110)_bcc，且原子平面(002)_hcp//(110)_bcc，hcp相比bcc相体积减小(0.33±0.02) cm³/mol；高压相hcp结构的晶格参数比值c/a=1.608±0.004；相变后原子配位数的增加使得hcp相(002)平面内及(002)平面间的最近邻原子间距比bcc相最近邻原子间距分别增大约1.6%和0.5%；用Murnaghan状态方程对实验数据进行最小二乘法拟合，得到bcc相B₀=(130±13) GPa，B₀'=12.6±0.5；hcp相V₀=(6.62±0.04) cm³/mol，B₀=(243±21) GPa，B₀'=6.8±0.3；对于该合金的bcc→fcp相变时的结构转变机制做了详细的讨论。     

Elastic constant measurement of Ni-base superalloy with the RUS and mode selective EMAR methods

This paper reports the elastic constants of the Ni-base single crystal superalloy (TMS-26) with a rafted (lamellar) structure having tetragonal symmetry. The elastic constants have been measured at room temperature with the resonance ultrasound spectroscopy method and the mode-selective electromagnetic acoustic resonance method. The value of the elastic constant C33 (250.4 GPa) is almost equal to that of c11 (252.5 GPa), which indicates that the rafted structure virtually has the elastic anisotropy of cubic system.     

Rhenium diboride's monocrystal elastic constants, 308 to 5 K

The five independent moduli required to construct the complete monocrystal elastic modulus tensor of the hexagonal-symmetry superhard compound ReB(2) were measured from 308 to 5 K using resonant ultrasound spectroscopy on a special-texture polycrystal. This is possible because, confirmed by X-ray diffraction, the specimen measured was composed of grains with hexagonal axes parallel so that its polycrystal elastic response is identical to a monocrystal and because hexagonal-symmetry solids are elastically isotropic in the plane perpendicular to the hexagonal axis. Along the hexagonal (c) axis, C(33) (0) = 1021 GPa, nearly equal to C(11) of diamond, and consistent with the superhard properties. However, in the (softer) isotropic plane, C(11) (0) = 671 GPa, much lower than diamond. The changes of C(ij) with temperature are very small and smooth. The Debye temperature was computed to be 738 K, and using a high-temperature approximation, the Gru?neisen parameter is γ = 1.7.     

The structure properties of LaNi3.5Al1.5

The structure properties of LaNi_3.5Al_1.5 have been investigated by the density functional theory using the full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The elastic constants of LaNi_3.5Al_1.5 are determined by a least-squares fitting of the calculated binding energy with a generalized two dimensional cubic function of lattice parameter a and c. The results show that the calculated lattice parameters (a=b=0.5092 nm and c=0.4214 nm) are in good agreement with the corresponding experimental data, that Al atoms prefer to substitute Ni atoms in the 3g sites and tend to disperse in middle planes. For LaNi_3.5Al_1.5, the bulk modulus (123.1 GPa), the shear modulus (68.6 GPa) and the values of the elastic constants C₁₁+C₁₂ (296.2 GPa), C₁₃ (76.4 GPa) and C₃₃ (210.5 GPa) are worked out for the first time. The ratio of c/a tends to increase from 0.790 (LaNi₅) to 0.804 (LaNi₄Al) and 0.827 (LaNi_3.5Al_1.5), which indicates that the LaNi_3.5Al_1.5 compound is observed to change less anisotropic with the substitution of Al atoms than the host alloy.     

立方结构Fe基磁性材料弹性系数第一性原理计算

通过赝势平面波法(CASTEP)及全电势线性缀加平面波法(FLAPW)，以bcc-Fe为对象，研究第一性原理计算立方结构Fe基磁性材料弹性系数的方法，分析影响计算立方结构Fe基磁性材料弹性系数准确度的各项因素. 结果表明，在第一性原理弹性系数计算中，晶格常数是决定弹性系数计算准确度的关键因素；势函数的选择也会影响计算准确度. 使用全电势基矢的FLAPW法可以得到更为精准的弹性系数计算结果. 计算得到bcc-Fe的弹性系数C₁₁，C₁₂，C₄₄分别为246 GPa，121 GPa，113 GPa，与实验值基本一致. 利用本方法，计算了新型Fe-Ga磁致伸缩材料的弹性系数C₁₁，C₁₂，C₄₄分别为207 GPa，166 GPa及108 GPa. 关键词： 弹性系数 磁致伸缩材料 赝势平面波法 全电势线性缀加平面波法     

First-principles investigation on the elastic stability and thermodynamic properties of Ti₂SC

Using Vanderbilt-type plane-wave ultrasoft pseudopotentials within the generalized gradient approximation(GGA) in the frame of density functional theory(DFT),we have investigated the crystal structures,elastic,and thermodynamic properties for Ti2SC under high temperature and high pressure.The calculated pressure dependence of the lattice volume is in excellent agreement with the experimental results.The calculated structural parameter of the Ti atom experienced a subtle increase with applied pressures and the increase suspended under higher pressures.The elastic constants calculations demonstrated that the crystal lattice is still stable up to 200 GPa.Investigations on the elastic properties show that the c axis is stiffer than the a axis,which is consistent with the larger longitudinal elastic constants(C 33,C 11) relative to transverse ones(C 44,C 12,C 13).Study on Poisson’s ratio confirmed that the higher ionic or weaker covalent contribution in intra-atomic bonding for Ti2SC should be assumed and the nature of ionic increased with pressure.The ratio(B/G) of bulk(B) and shear(G) moduli as well as B/C 44 demonstrated the brittleness of Ti2SC at ambient conditions and the brittleness decreased with pressure.Moreover,the isothermal and adiabatic bulk moduli displayed opposite temperature dependence under different pressures.Again,we observed that the Debye temperature and Gru¨neisen parameter show weak temperature dependence relative to the thermal expansion coefficient,entropy,and heat capacity,from which the pressure effects are clearly seen.     

Al的微观组态与LaNi3.75Al1.25的结构和弹性第一性原理研究

在全电子水平上，采用广义梯度近似密度泛函理论和全势能线性缀加平面波方法并结合二维立方拟合方法，对LaNi_3.75Al_1.25合金的晶体结构与弹性性质进行了理论研究.计算结果给出合金的晶格常数a=b=0.5137　nm，c=0.4018　nm，Al原子在晶胞中的微观分布为同时占据部分3g和2c等价格位，弹性常数C₁₁+C₁₂=281.2，C₁₃=82.3，C₃₃=227.3，以及体弹性模量B＝124.5、切变模量G＝68.2　GPa.还对态密度、能带结构和电荷密度进行了计算分析，并给出材料LaNi_3.75Al_1.25的电子线性比热系数23.45　mJ/molK². 关键词： 3.75Al_1.25')" href="#">LaNi_3.75Al_1.25 储氢合金 全势能线性缀加平面波 弹性常数     

高压下硫化钙的弹性和热力学性质的第一性原理计算

利用基于密度泛函理论的第一性原理平面波赝势方法结合准谐德拜模型研究NaCl结构的CaS在高压下的弹性和热力学性质.计算得到的零温零压下的晶格常数、体弹模量与实验值符合得很好.弹性常数和弹性模量随着压强的增大而增大.压强对体弹模量和热膨胀系数的影响大于温度的影响.热容随压强的升高而降低,在高温下热容接近于Dulong-Petit极限.通过求解Gibbs自由能计算得到B1结构和B2结构CaS的相变压为36.61 GPa.     

Measurement of the elastic constants of a columnar SiC thin film

The technique of resonant ultrasound spectroscopy was used to measure the elastic properties of a polycrystalline cubic silicon carbide (3C-SiC) thin film. The film, grown on a silicon (100) substrate, was 1.69 microns thick with columnar crystalline grains and a (111) texture. The substrate with the film was placed between two transducers and the resonant frequencies were measured; measurements were repeated after selective, timed dry etching of the film, allowing a determination of the elastic constants of the film alone. The film elastic constants, c(11)=371 and c(12)=146 GPa, were within a few percent of the literature values (c(11)=386, c(12)=136 GPa) of crystalline 3C-SiC. However, the film elastic constant c(44), 111 GPa, was significantly smaller than the bulk literature value, 254 GPa. For the film, c44 approximately (c(11)-c(12))/2, indicating that, quite unlike a bulk 3C-SiC crystal, the thin film is elastically isotropic.     

Elastic constants of solids at high pressures

The isothermal and adiabatic nth-order (n ?? 2) elastic constants of a loaded crystal are defined. These constants fully determine the behavior of solids at an arbitrary load and are controlled by both an interatomic interaction and an applied load. Expressions that relate these constants (of the second, third, and fourth order) to Brugger elastic constants of the corresponding order, which are only determined by an inter-atomic interaction, are found for cubic symmetry crystals under hydrostatic pressure. These expressions are used to calculate the equation of state and the second- and third-order elastic constants of bcc tantalum at T = 0 K over a wide pressure range (0?C600 GPa) using an electron density functional method. The results of calculating the equation of state and the second-order elastic constants agree with available experimental data and the calculation results obtained in other works.     

SmN晶体的电子结构和高压相变的第一性原理

利用基于密度泛函理论的第一性原理,研究了SmN晶体的电子结构和高压相变. SmN晶体的电子结构具有半金属特征,多数自旋电子显示金属导电性,少数自旋电子显示半导体导电性. 高压相变的结果显示,SmN晶体经历从NaCl型(B1)到CsCl型(B2)结构转变的压致结构相变,相变压力117 GPa. 弹性系数的结果显示,在环境压力下SmN晶体的弹性系数满足玻恩稳定条件,标志着B1相是力学稳定结构. 声子谱结果显示,在环境压力下B1相是热力学稳定结构,与弹性系数的计算结果一致.