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.     

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.     

晶格应变理论及其应用

20世纪90年代Singh等人建立了基于非静水压缩的晶格应变理论。这一理论的建立使非静水压环境下状态方程的精确测量成为可能,同时也开辟了材料弹性常数测量的新方法。目前,这一理论在材料状态方程研究、强度研究、弹性研究和实验数据分析诸多领域有着广泛的应用。文中主要介绍晶格应变理论及其应用,并简要介绍我们利用晶格应变理论对高压下NiO弹性性质的研究结果。