Evidence of polymorphic transformations of Sn under high pressure

The high-pressure polymorphs and structural transformation of Sn were experimentally investigated using angledispersive synchrotron x-ray diffraction up to 108.9 GPa. The results show that at least at 12.8 GPa β-Sn→bct structure transformation was completed and no two-phase coexistence was found. By using a long-wavelength x-ray, we resolved the diffraction peaks splitting and discovered the formation of a new distorted orthorhombic structure bco from the bct structure at 31.8 GPa. The variation of the lattice parameters and their ratios with pressure further validate the observation of the bco polymorph. The bcc structure appears at 40.9 GPa and coexists with the bco phase throughout a wide pressure range of40.9 GPa–73.1 GPa. Above 73.1 GPa, only the bcc polymorph is observed. The systematically experimental investigation confirms the phase transition sequence of Sn as β-Sn→bct→bco→ bco + bcc→bcc upon compression to 108.9 GPa at room temperature.     

DAC加载下材料高压声速的激光超声测量技术

 设计并建立了可测量金刚石压砧（DAC）加载下材料高压声速的激光超声系统。该系统采用脉宽为6.3 ns的调Q激光器作为超声波激发光源,使用光纤位移干涉仪和速度干涉仪混合系统进行超声位移探测,不需要借助其它任何参数即可直接测量样品的高压声速和原位厚度。利用该系统,测量了2.6 GPa压力下铜样品的高压纵波声速和原位厚度,并给出了测量结果。     

SrB_4O_7掺杂二价镧系离子的荧光光谱特性研究

采用高温固相法通过掺杂不同种类的镧系元素以及改变掺杂元素的浓度制备了系列SrB_4O_7∶Re~(2+)(Re代表Ce,Nd,Gd和Lu)荧光材料,利用实验室自建的非偏振显微共聚焦荧光/拉曼测量系统重点研究了其荧光光谱特性。研究发现,SrB_4O_7∶Re~(2+)和SrB_4O_7∶Sm~(2+)具有相似的荧光特性,最强单峰对应~5 D_0-~7 F_0电子跃迁所产生的荧光峰(0-0峰),峰位为685.41nm;在700和730nm附近还对应有~5 D_0-~7 F_1和~5 D_0-~7 F_2电子跃迁所产生的两条强度较弱的荧光带;在相同条件下,SrB_4O_7∶Re~(2+)的0-0峰强度较SrB_4O_7∶Sm~(2+)的0-0峰强度至少要弱一个量级。对SrB_4O_7∶Re~(2+)荧光光谱分析结果显示,掺杂元素种类和掺杂元素浓度是影响荧光光谱强度的关键因素,两者直接决定了能参与发光的Re~(2+)离子的总量。     

γ-Ce中的高压纵波声子模软化和状态方程描述

利用同步辐射角散X射线衍射技术测量了室温条件下0---0.74 GPa 压力范围内Ce的等温压缩线.发现γ-Ce的室温等温压缩线呈外凸形, 这是由其纵波声子模软化所致.利用超声测量得到的体弹性模量随压力变化的规律, 对实验所得到的压力与体积数据, 用二阶和三阶Murnaghan 方程、 二阶和三阶Birch 方程、 三阶Xu方程以及二阶Vinet方程进行比较, 并且对这些状态方程得到的体弹性模量随压力的变化规律与超声实验的结果相对比, 发现三阶Murnaghan 方程和三阶Xu方程对γ-Ce最适用.     

利用激光超声技术测量介观尺度材料的声速

设计并建立了一种可用于测量介观尺度(几十微米至几毫米)材料声速的激光超声系统.该系统采用脉宽为6.3 ns的调Q激光器作为超声波激发光源,使用光纤位移干涉仪进行超声位移探测.利用新建立的激光超声系统,测量了不同厚度铜箔的纵波声速.结果表明,激光超声系统得到的声速具有较高精度,可以将其应用于介观尺度材料声速测量.     

锡和氙离子在13.5 nm波长附近的光谱特性

 应用多组态Dirac-Fock方法,系统计算了锡（Sn）和氙（Xe）离子在13.5 nm波长附近的辐射跃迁波长和跃迁几率。深入分析了^(7~13)+Sn和Xe^(7~13)+离子跃迁的原子光谱特性,研究了相对论效应和电子关联效应对能级位置和跃迁几率的影响发现,相对论效应和电子关联效应对光谱能量的影响分别为2%和5%。并从光谱特性的角度对比讨论了Sn和Xe作为极端远紫外光源的优劣,发现Sn更有优势。     

Unusual softening behavior of yield strength in niobium at high pressures

In situ synchrotron angle-dispersive x-ray diffraction experiments on niobium powders have been conducted at pressures up to 61 GPa and room temperature using the diamond anvil cell technique. From the full width at half maximum of the measured diffraction lines, the yield strength was derived with the line-width analysis theory. The niobium powder sample was found to be compressed more packed firstly and then yielded at~14 GPa–18 GPa. Following an initial increase in the yield strength with pressure, an obvious decrease was observed occurring at ~42 GPa–47 GPa accompanying with a typical pressure dependence above 47 GPa. The experimentally observed anomalous softening of the yield strength in niobium surprisingly follows the trend of the predicted unusual softening in the shear modulus by the recent theoretical investigations. The possible mechanisms, applicable to interpret the yield strength softening of materials at high pressure,were also discussed in detail.     

原位测量金刚石压砧在高压下的杯型形变

基于白光频域干涉的基本原理,提出了一种可实现高压下金刚石压砧杯型形变原位测量的方法。简单介绍了利用频域干涉技术测量金刚石压砧在高压下的杯型形变的基本原理,并开展了实验研究,实验最高压力达到42.1GPa。实验结果显示,金刚石压砧的杯型形变与压力呈线性关系,最大值达到11.1μm,从实验上证实了最近的有限元数值模拟结果。     

Static strength of gold compressed up to 127 GPa

Gold powder is compressed non-hydrostatically up to 127 GPa in a diamond anvil cell(DAC),and its angle dispersive X-ray diffraction patterns are recorded.The compressive strength of gold is investigated in a framework of the lattice strain theory by the line shift analysis.The result shows that the compressive strength of gold increases continuously with the pressure up to 106 GPa and reaches 2.8 GPa at the highest experimental pressure(127 GPa) achieved in our study.This result is in good agreement with our previous experimental result in a relevant pressure range.The compressive strength of gold may be the major source of the error in the equation-of-state measurement in various pressure environments.