High-pressure phase transition of Bi2Fe4O9

The high-pressure behaviour of Bi2Fe4O9 was analysed by in situ powder and single-crystal x-ray diffraction and Raman spectroscopy. Pressures up to 34.3(8) GPa were generated using the diamond anvil cell technique. A reversible phase transition is observed at approximately 6.89(6) GPa and the high-pressure structure is stable up to 26.3(1) GPa. At higher pressures the onset of amorphization is observed. The crystal structures were refined from single-crystal data at ambient pressure and pressures of 4.49(2), 6.46(2), 7.26(2) and 9.4(1) GPa. The high-pressure structure is isotypic to the high-pressure structure of Bi2Ga4O9. The lower phase transition pressure of Bi2Fe4O9 with respect to that of Bi2Ga4O9 (16 GPa) confirms the previously proposed strong influence of cation substitution on the high-pressure stability and the misfit of Ga3+ and Fe3+ in tetrahedral coordination at high pressure. A fit of a second-order Birch–Murnaghan equation of state to the p–V data results in K0 = 74(3) GPa for the low-pressure phase and K0 = 79(2) GPa for the high-pressure phase. The mode Grüneisen parameters were obtained from Raman-spectroscopic measurements.     

Effect of a fullerene C60 addition on the strength properties of nanocrystalline copper and aluminum under shock-wave loading

The Hugoniot elastic limit and the spall strength of aluminum and copper samples pressed from a mixture of a metallic powder and 2–5 wt % C₆₀ fullerene powder are measured under a shock loading pressure up to 6 GPa and a strain rate of 10⁵ s^?1 by recording and analyzing full wave profiles using a VISAR laser interferometer. It is shown that a 5% C₆₀ fullerene addition to an initial aluminum sample leads to an increase in its Hugoniot elastic limit by an order of magnitude. Mixture copper samples with 2% fullerene also exhibit a multiple increase in the elastic limit as compared to commercial-grade copper. The elastic limits calculated from the wave profiles are 0.82–1.56 GPa for aluminum samples and 1.35–3.46 GPa for copper samples depending on the sample porosity. The spall strength of both aluminum and copper samples with fullerene additions decreases approximately threefold because of the effect of high-hardness fullerene particles, which serve as tensile stress concentrators in a material under dynamic fracture.     

无钴合金钢的冲击响应实验研究

 利用一级轻气炮作为加载手段,研究了无钴合金钢在3~20 GPa压力区间的冲击响应特性。用激光干涉测速——VISAR记录了双波结构的自由面速度剖面,并利用常压下的弹性纵波速度近似替代低压冲击下的弹性先驱波速度,确定了无钴合金钢的Hugoniot关系。根据自由面速度反映的层裂信息,给出了无钴合金钢的Hugoniot弹性极限、层裂强度以及层裂片厚度等动态力学参数。     

冲击加载下Zr51Ti5Ni10Cu25Al9金属玻璃的塑性行为

进行了10—27 GPa应力范围内Zr₅₁Ti₅Ni₁₀Cu₂₅Al₉金属玻璃的平面冲击实验以研究其高压-高应变率加载下的塑性行为.由样品自由面粒子速度剖面的分析获得了冲击加载过程的轴向应力,并通过轴向应力与静水压线的比较获得剪应力.实验结果表明,尽管存在明显的松弛效应,但Zr基金属玻璃的Hugoniot弹性极限随着冲击应力的增加而增加.然而,塑性波阵面上的剪应力则显示先硬化而后软化现象,而且软化的幅度随冲击应力的增加而增加.冲击加载下Zr基金属玻璃的上述剪应力变化特征与分子动力学模拟结果比较一致,但与压剪实验结果和一维应力冲击实验结果明显不同.     

Shock-wave compression of x-cut quartz as determined by electrical response measurements

The mechanical response of x-cut quartz in the vicinity of the Hugoniot elastic limit is determined from measurements of the piezoelectric current from samples impact loaded from 26 to 130 kbar. The Hugoniot elastic limit is determined to be 60_?1·5⁺³ kbar at a compression of 0·066_?0·002^+0·004 This Hugoniot elastic limit corresponds to a shear strength of 5·5 per cent of the C₄₄ shear modulus. For stresses well above the Hugoniot elastic limit the electrical current measurements show that the material exhibits a substantial reduction of shear strength. The pressure derivative of the bulk modulus is determined to be 4·5, substantially less than the ultrasonic value. The experimental records show evidence for a time delay for reduction of shear strength which varies from about 10^?7 sec immediately above the 60 kbar Hugoniot elastic limit to about 10^?8 sec for stresses well above the Hugoniot elastic limit. The measurements also show stress relaxation below the Hugoniot elastic limit between 40 and 60 kbar.     

Shock compressing diamond to a conducting fluid

Laser generated shock reflectance data show that diamond undergoes a continuous transition from optically absorbing to reflecting between Hugoniot pressures 600相似文献   

静-动加载相结合的材料状态方程实验平台的研制

根据神光-Ⅱ第九路高功率激光加载的特点,对传统静高压金刚石压砧装置进行了改进和优化设计,研制出了适合高功率激光加载条件下材料宽域状态方程研究的新型静高压靶.在神光-Ⅱ高功率激光装置上建立了基于静高压金刚石压砧和动高压激光相结合的材料宽域状态方程研究平台.利用这一平台开展了超纯水的宽域状态方程实验探索,获得了较好的实验结果.     

Behavior of disordered boron carbide under stress

Gibbs free-energy calculations based on density functional theory have been used to determine the possible source of failure of boron carbide just above the Hugoniot elastic limit (HEL). A range of B4C polytypes is found to be stable at room pressure. The energetic barrier for shock amorphization of boron carbide is by far the lowest for the B12(CCC) polytype, requiring only 6 GPa approximately = P(HEL) for collapse under hydrostatic conditions. The results clearly demonstrate that the collapse of the B12(CCC) phase leads to segregation of B12 and amorphous carbon in the form of 2-3 nm bands along the (113) lattice direction, in excellent agreement with recent transmission electron microscopy results.     

Gold under high pressure

Abstract

First principle predictions for the equation of state of gold using solid and liquid state theories are compared up to combined pressures and temperatures of 600 GPa and 17 000 K with static diamond anvil cell compression, ultrasonic measurements and shock Hugoniot data which include a recent laser driven shock Hugoniot points at 600 GPa. Excellent agreement between theoretical and experimental data is observed. The theoretically estimated 300 K isotherm agrees to within 2 GPa with the isotherm that has been measured to 70 GPa using the diamond anvil cell. The structural energy estimates show that the normal f.c.c. phase remains stable under pressure. The estimate of the shock Hugoniot temperature of gold at 600 GPa based on a liquid state model is consistent with the measurements of laser induced shock luminescence, which in fact provides an experimental determination of the temperature of gold above its Hugoniot melting point. The powerful means provided by theory in the prediction of material properties of gold at ultra high pressures and temperatures is significant because gold is an efficient converter of laser energy into soft X-rays and is a potential candidate as a standard for high pressure, high temperature work.     

Planar spin fluctuations with a quadratic thermal dependence rate in spin liquid Gd3Ga5O12

The spin liquid properties of Gd3Ga5O12 have been examined using 155Gd M?ssbauer spectroscopy down to 0.027 K. Information has been obtained concerning both the directional properties of the short range correlated moments and the thermal dependence of their spin fluctuation rates. Each Gd3+ spin (S=7/2) is found to be confined to a plane and its fluctuation rate decreases from approximately 2.8 x 10(9) s(-1) at 0.4 K to approximately 0.03 x 10(9) s(-1) at 0.09 K following a close-to-quadratic thermal dependence.     

碳水混合物冲击压缩特性的理论研究

 采用固-液双相混合模型和分子流体的微扰变分统计理论,分别计算了石墨-水体系（ρ₀=1.233 g/cm³）和金刚石-水体系（ρ₀=1.238 g/cm³）的冲击压缩特性。结果表明：（1）在不发生石墨→金刚石相变和化学反应的低压区域（p<20 GPa）,这两种混合体系的冲击压缩曲线的差别并不明显;（2）在发生石墨→金刚石相变的高压区域（p>20 GPa）,这两种混合体系的冲击压缩曲线显著不同,且石墨-水体系更易压缩;（3）在45～60 GPa强冲击压力范围内,冲击波诱发的化学反应也不会显著影响这两种体系冲击压缩曲线的走势。上述结论与文献（高压物理学报,1999,13(2):87-92）发表的实验结果相矛盾。进一步分析了引起理论与实验结果不一致的可能原因,并对文献中的实验结果及其理论分析结论提出质疑。     

Gd3Ga5O12:Ag薄膜电致发光材料的制备及其发光性质

研究了Gd3 Ga5O12 :Ag材料的制备及其发光性质 .Gd3 Ga5O12 :Ag材料通过固相反应法制得 ,采用X射线衍射法分析了材料的结晶度及成分 .用电子束蒸发将该材料制备成交流的薄膜电致发光器件 ,得到了较好的蓝紫色发光 ,发光峰分别位于 397和 46 7nm .通过对材料的光致发光和激发光谱的研究和比较 ,得出 397和 46 7nm分别来自于氧空位和Ag 的发光 .     

Elastic-plastic deformation and fracture of shock-compressed single-crystal and polycrystalline copper near melting

The Hugoniot elastic limit, the yield strength, and the spall strength of polycrystalline M1 copper and single-crystal (110) and (111) copper are determined during shock compression up to 8 GPa in the temperature range 20–1080°C from an analysis of the free-surface velocity profiles recorded with VISAR laser velocimeter. The measurements show that all copper samples exhibit strong athermal hardening (increase in the Hugoniot elastic limit) near the melting temperature. Copper single crystals have a very low elastic limit in the temperature range up to 600°C, this limit increases sharply as the temperature increases to 1000°C, and it depends on the crystallographic orientation of a single crystal. The temperature dependence of the spall strength has a threshold character for all copper samples. Copper single crystals demonstrate higher resistance to spall fracture; however, near the melting temperature, the difference between the spall strengths of the copper single crystals and M1 copper becomes insignificant, 50% of the initial level.     

Strength and failure of LK7 borosilicate glass under shock compression

The Hugoniot elastic limit (HEL), the spall strength, the failure threshold, and the failure wave velocity in LK7 glass during shock compression are measured. The HEL estimated from the profiles of compression waves of various intensities is 7.1 ± 0.1 GPa. The spall strength exceeds 7 GPa during shock compression in the elastic range and remains high when passing through the HEL. Failure waves form in the stress range from 5.7 to 10.3 ± 0.5 GPa.     

Coupling static and dynamic compressions: first measurements in dense hydrogen

We demonstrate here a laser-driven shock wave in a hydrogen sample, pre-compressed in a diamond anvil cell. The compression factors of the dynamic and static techniques are multiplied. This approach allows access to a family of Hugoniot curves which span the P–T phase diagram of fluid hydrogen to high density. In this first-of-its-kind experiment, two hydrogen Hugoniot curves have been partially followed starting from pre-compression at pressures of 0.7?GPa and 1.2?GPa. Optical reflectance probing at two wavelengths reveals the onset of the conducting fluid state. The boundary line to conducting fluid hydrogen is suggested.     

Shock compressibility of polycrystalline nickel aluminide

ABSTRACT

We present experimental data on Hugoniot and release isentropes of nickel aluminide obtained for shock pressures up to 83?GPa and make comparison with previously published calculation data. We estimate a Hugoniot elastic limit of samples, construct the EOS of nickel aluminide and investigate the Hugoniot position relative to the melting curve.     

Shock-induced phase transitions in the MgO-FeO system to 200 GPa

We report new shock-compression data for single-crystal MgO at 114 and 192 GPa. Our data together with the existing shock-wave data revealed a volume discontinuity at 170±10 GPa along with the MgO Hugoniot. The discontinuity gives a volume increase of 1.9%, indicating a possible phase transition from a rock-salt structure (B1) to a high-temperature phase along with the MgO Hugoniot. We re-examined the Hugoniot data on polycrystalline sample (Mg_0.6, Fe_0.4)O up to 200 GPa [M.S. Vassiliou, T.J. Ahrens, The equation of state of Mg_0.6Fe_0.4O to 200 GPa, Geophys. Res. Lett. 9 (1982) 127-130], which showed similar discontinuity with a 2.2% volume increase at 135±10 GPa. Our results add to fundamental understandings of the behavior of MgO and the lower mantle mineral magnesiowüstite (Mg, Fe)O at ultrahigh pressure and temperature.     

电磁内爆的准一维数值模拟

 提出一个用于电磁内爆过程数值模拟的准一维模型，对1 MJ电容器组电磁内爆优化方案进行了计算，并将计算结果与零维模型和一维模型的结果进行了比较。     

Study of cerium phase transitions in shock wave experiments

Cerium has a complex phase diagram that is explained by the presence of structural phase transitions. Experiments to measure the sound velocities in cerium by two methods were carried out to determine the onset of cerium melting on the Hugoniot. In the pressure range 4–37 GPa, the sound velocity in cerium samples was measured by the counter release method using manganin-based piezoresistive gauges. In the pressure range 35–140 GPa, the sound velocity in cerium was measured by the overtaking release method using carbogal and tetrachloromethane indicator liquids. The samples were loaded with plane shock wave generators using powerful explosive charges. The onset of cerium melting on the Hugoniot at a pressure of about 13 GPa has been ascertained from the measured elastic longitudinal and bulk sound velocities.     

十种稀土金属电阻的压力效应

 使用Bundy和Dunn发展起来的带有烧结金刚石砧的Drickamer型高压装置，用固定点测压法标定实验压力，在室温及0~43 GPa的压力范围内测量了稀土金属中Pr、Nd、Sm、Gd、Tb、Dy、Ho、Tm、Lu和Yb的电阻随压力的变化。在各稀土元素的电阻随压力变化的曲线上，观测到了若干“凸起”和斜率突变点，根据Jayaraman提出的三价稀土在压力作用下的相变顺序，得到了这些突（凸）变点分别对应着hcp→Sm-type→dhcp→fcc相变顺序中的某一类型的相变压力。此外还观测到了Pr、Gd、Tb的fcc相随着压力再增高而发生的相变，根据已报导的关于Pr的工作，推测Gd和Tb的这一相变应为fcc→dfcc相变，它们分别发生在22.0和24.5 GPa。在本工作所得结果基础上对Johansson的三价稀土总相图进行了修正。