High pressure synthesis of LiMeO2–ZnO (Me=Fe 3+, Ti3+) solid solutions with a rock salt structure

Metastable LiMeO₂–ZnO (Me=Fe ³⁺, Ti³⁺) solid solutions with a rock salt crystal structure have been synthesized by the solid-state reaction of ZnO with LiMeO₂ complex oxides at 7.7 GPa and 1350–1450 K. The structure, phase composition, thermal stability and thermal expansion of the recovered samples have been studied by X-ray diffraction with synchrotron radiation. At ambient pressure, rock salt LiMeO₂–ZnO solid solutions are kinetically stable up to 670–800 K, depending on the composition.     

Ca5N4高压新相的第一性原理研究

通过在氮中引入杂质离子,利用高压手段获得具有新奇结构的多氮化合物是目前被广泛应用的研究方法.钙氮材料在催化、光电方面有着广泛的应用.具有较低电离能的钙(Ca)元素很容易和氮原子形成离子键钙氮化物.高压为寻找新型钙氮化合物提供了全新的技术途径.因此,利用高压方法,通过改变配比的方式,寻找具有新奇特性的钙氮高压结构,是一项...     

人造金刚石的制备方法及其超高压技术

介绍了天然金刚石的生长机理和人造金刚石的发展历史,从静压法、动压法和低压法3种方法概述了人造金刚石制备方法的研究现状;针对4种现今普遍使用的金刚石合成装置,即两面顶、四面顶、六面顶和分割球高压装置,阐述了其结构设计和使用现状;总结了金刚石行业目前存在的主要问题,并对其发展趋势进行了展望。

     

KNb0.77Al0.23O2.77的高压相变研究

 利用水热法合成了立方相KNb_0.77Al_0.23O_2.77。在水热晶化过程中得到了包括正交相钙钛矿和一新相在内的中间相产物。结构相变行为采用XRD、DSC、高压Raman和XPS进行了表征。结果表明,低于1 000 ℃的热处理不能导致KNb_0.77Al_0.23O_2.77发生结构相交。而在4.49 PGa高压下可能发生了到一新相的结构转变。高温高压处理可以导致另一新相的出现。最后对该立方相的相变机理进行了研究。     

某些稀土氧化物的高温高压合成及其结构稳定性研究

 首次用高压高温方法,在3.2~4.0 GPa,1 000~1 300 ℃下,对CeO₂-R₂O₃（R=Eu,Gd）,CeO₂-Tb₄O₁₁,Pr₆O₁₁-Tb₄O₇稀土氧化物进行合成实验,得到具有F型结构的CeEuO_3.5,CeGdO_3.5,CeTbO_3.5;B型结构的CeEuO₃,CeGdO₃,CeTbO₃,PrTbO₃和P型结构的PrTbO₃。PrTbO₃是迄今自然界尚未发现,文献未见报导过的新物质。对上面的产物和NdYbO₃、PrTmO₃,利用高、低温X射线衍射实验,检测了其结构的稳定性,结果指出：从300 ℃直到1 000 ℃,发生由B型CeRO_x向F型CeRO_x（R=Eu,Gd,Tb）、B型PrTbO₃向C型PrTbO₃的结构转变。F型CeRO_x属于氧缺位萤石型结构。     

高压下铁的电导率及X射线衍射研究

用四点电极法及磁控溅射结合光刻集成电极的方法,测量了铁在25 GPa压力下的电阻随压力的变化;用微区X射线衍射仪原位测量了铁在25 GPa压力下晶胞参数随压力的变化关系。实验结果表明,铁在13.7 GPa时发生相变,由体心立方相转变为六方密堆相,在18.1 GPa时相变结束。利用高压下铁的电阻数据,结合X射线衍射结果,推导出铁的电导率随压力的变化关系。     

从碳化硅和铁体系合成金刚石

 为了探明从SiC生成金刚石这一过程中触媒作用的机理,有必要调查SiC加不同金属在高压高温下的行为。在本工作中,以16重量比混合的SiC和铁粉经5.4~6.0 GPa的高压力和1 300~1 500 ℃的高温处理20 min后,样品的X射线衍射分析表明：所有实验条件下SiC都发生了分解,并分别生成了Fe₃Si和Fe₃C;温度越高,SiC分解得越彻底,在温度高于1 375 ℃的样品中,伴随Fe₃C减少,有金刚石和石墨明显析出。扫描电镜观察表明：6.0 GPa、1 500 ℃下所得的金刚石晶体具有完整的八面体晶形,平均粒度约50 μm。     

Synthesis experiments on in-Sb and B-Sb systems in a laser heated diamond-anvil cell

Abstract

High pressure and high temperature synthesis experiments were carried out on In-Sb and B-Sb systems with a laser heated diamond-anvil cell. InSb was synthesized starting from In and Sb at various pressures ranging from 0.2 to 10 GPa. The cubic as well as the high pressure phases were successfully synthesized. Experiments above 8 GPa, wherein antimony exists in the tetragonal phase, have revealed no new phases of InSb. Trials of synthesizing a compound from B and Sb gave negative result to at least 30 GPa.     

高温高压下液态铁的状态方程

基于高温高压下面心立方(FCC)铁的状态方程和熔化温度实验数据,建立了热力学模型计算FCC铁、固-液混合相、液态铁在高温高压下的状态方程.在相同密度和温度下,计算的FCC铁、固-液混合铁、液态铁的压强与实验测量结果较为一致,且计算结果与实验结果平均偏差分别为-1.61 GPa、1.05 GPa、-0.05 GPa.在0～100 GPa压强范围内,当铁完全发生熔化时,随着压强的增大其密度变化由-7.5%下降至2.7%.     

On-line laser heating setup for ED-XAS at ID24: preliminary optical design and test results

Double-sided laser heating (LH) combined with synchrotron X-ray radiation for in situ studies in the diamond anvil cell (DAC) has been the most productive and widely used high-temperature–high pressure technique in the past two decades. In the framework of the UPBL11 project (upgrade of ID24 beamline of European Synchrotron Radiation Facility), we developed a new on-line LH system for DACs. The preliminary optical scheme of the system is presented and discussed. Varying the settings, we are able to shape and to size the beam on the surface of the sample in the DAC. First pilot applications to the Fe case are shown.     

Effect of pressure on thed-spacings of the quasicrystal Al-18 a/o Fe

We report the high pressure X-ray studies of quasicrystal Al-18 a/o Fe. It is observed that initially thed-spacings decrease monotonically with pressure, but at 57 kbar there is a sudden fall, indicative of a first order phase transition. The compression and the discontinuities are observed to be highly directional.     

Rietveld analysis of high pressure powder diffraction data

Abstract

X-ray and neutron powder diffraction data obtained from samples contained within high pressure cells are generally of lower quality than data collected from samples at ambient conditions. The far smaller sample size as well as possible contamination of the pattern by the pressure cell means that Rietveld refinement techniques must be adapted to extract the maximum useful information from the data. These problems become paramount as larger structures at high pressure are attempted. Techniques such as “leBail extraction”, “soft restraints” and “rigid body refinement” will be discussed with application to analysis of high pressure neutron powder diffraction data.     

High pressure raman studies of GaAs/A1As superlattices: folded-acoustic phonons and resonant second-order scattering

Abstract

Materials containing light elements and characterized by a dense structure present specific physico-chemical properties.

The carbonitrides C_xN_y, and in particular C₃N₄, have attracted the attention of the scientific community during these last ten years.

The main chemical problem in the synthesis of such materials is to introduce nitrogen into the lattice, due to the strong stability of N₂.

In order to prevent nitrogen loss, the use of high pressures and the selection of nitriding media can be developed.

The present contribution describes the main results obtained through two routes:

(i) the thermal decomposition of precursors containing carbon and nitrogen under high pressure conditions (2-6GPa) (without or with nitrogen solvent)

(ii) the high pressure condensation of “organic” precursors containing carbon and nitrogen.