用于高压原位中子衍射的PCBN压腔

基于多晶立方氮化硼(PCBN)的高硬度以及对中子良好的吸收性,选用PCBN作为压砧材料,设计了一种新型外凹式平面压砧以及由钛锆合金、碳纤维管、聚四氟乙烯组成的复合封垫。使用该PCBN压腔,分别利用ZnTe和ZrW2O8的相变点对腔体压力进行标定。结果表明:当样品腔体积为9mm3、负载压力为260kN时,腔内压力达到9GPa。高压原位中子衍射实验显示,采用外凹式PCBN压腔得到了无压砧背底信号的铁的高压中子衍射谱。预计通过进一步优化,利用PCBN压腔可获得更高压力(10GPa以上)下高质量高压中子衍射谱。

Electrical Characterization in the Phase Transition between Cubic PbCrO_(3) Perovskites at High Pressures

By in situ x-ray diffraction,an isostructural phase transition between two kinds of the cubic PbCrO_(3) perovskites at around 1.6 GPa and room temperature with a 9.8%volume change is discovered.Recently,we have synthesized this cubic PbCrO_(3)perovskite successfully.Here we report our high-pressure in situ electrical resistance measurements up to 4.1 GPa for this perovskite sample.At room temperature,the resistance shows special changes at 1.2 and 2.7 GPa.They may indicate the starting and ending points of this transformation.At 4.1 GPa,the negative temperature resistance coefficient is observed,which means that phase Ⅱ could be considered as a semiconductor according to our present measurement.

Isotropic Thermal Expansivity and Anisotropic Compressibility of ReB2

We experimentally investigated some of the mechanical properties of ReB2 under high temperature/pressure(TIP)conditions.High-T experiments(up to 600℃at 1 atm)were carried out in a high-T oven attached to a conventional x-ray diffractometer whereas high-P experiments(up to about 42 GPa at 25℃)were conducted in a diamond-anvil cell using synchrotron x-ray radiation.High-T data suggest a highly isotropic thermal expansivity whereas high-P data suggest a highly anisotropic compressibility for ReB2.

Solidification of Undercooled Ge_(73.7)Ni_(26.3) Alloy Subjected to Sputtering-Deposition of Ni Clusters

Undercooled melt of Ge_(73.7)Ni_(26.3) alloy sample floated on B_(2)O_(3 ) melt was subjected to sputtering-deposition of Ni clusters on cooling to induce solidification.The initial temperature of solidification was 975 K.Its undercoolingΔT was 134 K with respect to the melting temperature of the primary phase Ge.On the cooling curve existed dual recalescences representing the transformation of the primary phase(Ge)and the eutectics(Ge+GeNi)respectively.But for the sample unsputtered,only a single exothermic peak presented on the cooling curve with the initial solidification temperature of 904K and undercooling of 205K.Careful observation of the microstructure proved that the Ge phase primarily formed in the sputtering experiment was now formed together with the formation of the eutectics in the experiment without sputtering.

Solid/Liquid Interface of Ag/Sn/Ag Trilayers by In Situ Resistivity Measurement

The in situ four-point probe resistivity measurement was used as a main method to study the solid/liquid interfacial characteristics in Ag/Sn/Ag trilayers at temperatures ranging from 150 to 305℃.It is found from the variation of resistivity that three processes take place on annealing:the dissolution of silver atoms,the diffusion of silver atoms,and the formation of Ag3Sn in liquid tin layer.The first one plays the leading role in the variation of resistivity during annealing process.The apparent diffusivity of silver in liquid tin at 305℃ is determined to be 7.3×10^(-17)cm^(2)/s.

大腔体静高压技术的发展及应用

大腔体静高压技术在现代工业和高压科学研究中具有基础性的重要意义,已被广泛应用于工业和科研领域,如超硬材料的合成、凝聚态物质在高温高压极端条件下的行为与物性研究等。经过逾半个世纪的不懈努力,以国产铰链式六面顶压机为代表的大腔体静高压技术与设备取得了长足的发展和丰硕的成果,改变了长期以来我国大腔体静高压技术落后于国外的局面。文章以四川大学高压科学与技术实验室为例,对我国大腔体静高压技术及装置从起步研制到世界领先的发展历程和技术特点进行了介绍。同时,基于典型大腔体静高压技术、装置及主要应用,展望了我国相关领域的发展前景。