Exploring the compression behavior of HP-BiNbO_4 under high pressure

In the present work, a third form, the so-called HP-BiNbO_4 synthesized at high pressure and high temperature is investigated with the in-situ angle-dispersive x-ray diffraction(ADXRD) measurements under high pressure. We explore the compression behavior and phase stability of HP-BiNbO_4. The structure of HP-BiNbO_4 is first determined. The x-ray diffraction data reveal that the structure HP-BiNbO_4 is stable under pressures up to 24.1 GPa. The ADXRD data yield a bulk modulus K_o = 185(7) GPa with a pressure derivative K_o'= 2.9(0.8). Furthermore, the data are compared with those of other ABO_4 compounds. The results show that the bulk modulus of HP-BiNbO_4(about 185 GPa) is slightly higher than that of tetragonal BiVO_4 and significantly greater than those of the tungstates and molybdates.     

二次加压对六面顶压腔压力发生效率和 压力密封性能的影响

随着六面顶压机大腔体静高压技术的发展,复杂多变的压力加载工艺被应用于高压科学研究和材料制备,但是不同压力加载工艺对压力发生效率和压力密封性能的影响尚未被充分研究。本工作在六面顶压机高压腔体和密封边内置入电路,通过原位测量Bi、Tl、Ba和锰铜丝的电阻,标定了一次加压和二次加压两种不同压力加载工艺下外部加载与腔体压力及密封边压力的对应关系。实验分析结果表明,二次加压工艺会导致腔体和密封边的压力发生效率明显降低,同时也会降低压力密封性能最差时对应的外部加载。此研究可为高压装置和压力加载工艺的优化设计提供指导。     

低掺杂La_(1-x)Sr_xMnO_3结构相变对其电磁特性的影响

高温高压条件下，低掺杂的Ｌａ１－ｘＳｒｘＭｎＯ３化合物发生从菱方相（Ｒ３ｃ）到立方相的转变，该相变使其从低温时的绝缘态（极化子有序）转变为金属态．同时，随温度的降低，局域锰离子的自旋也从铁磁长程有序变成了只有短程序结构的自旋玻璃态．这种转变是由于相变引起的Ｍｎ—Ｏ—Ｍｎ键角及Ｍｎ—Ｏ键长的改变所引起．     

Equal compressibility structural phase transition of molybdenum at high pressure

We have studied the high-pressure compression behavior of molybdenum up to 60 GPa by synchrotron radial x-ray diffraction (RXRD) in a diamond anvil cell (DAC). It is found that all diffraction peaks of molybdenum undergo a split at around 27 GPa, and we believe that a phase transition from a body-centered cubic structure to a rhombohedral structure at room pressure has occurred. The slope of pressure-volume curve shows continuity before and after this phase transition, when fitting the pressure-volume curves of the body-centered cubic structure at low pressure and the rhombohedral structure at high pressure. A bulk modulus of 261.3 (2.7) GPa and a first-order derivative of the bulk modulus of 4.15 (0.14) are obtained by using the nonhydrostatic compression data at the angle ψ = 54.7° between the diffracting plane normal and stress axis.     

力学结构及末级压砧硬度对八面体压腔高压发生效率的影响

针对大腔体静高压装置中的多级八面体压腔,分析了两种不同加载结构的力的传递, 建立了高压发生效率的力学关系.室温下,采用定点标压法(Bi, ZnTe, ZnS, GaAs)分别标定了14/8, 12/6和10/4三种二级6-8型大腔体静高压组装的腔体压力, 定量地讨论了力学结构和末级压砧硬度对八面体压腔高压发生效率的影响. 实验结果表明,力学结构和末级压砧硬度都是影响高压发生效率的重要因素, 且力学结构对高压发生效率的影响更大.其中,腔体的几何结构越大,高压发生效率越高; 6-8型加载结构的高压发生效率高于2-6-8型加载结构;在八面体压腔内的压力接近末级压砧的维氏硬度时, 末级压砧硬度越大,高压发生效率越高,所能获得的腔体压力越大.