Semimetal States of Crystalline Molecular Hydrogen at High Pressures

JETP Letters - Semimetal states of crystalline molecular hydrogen have been obtained at a temperature of 100 K in the pressure range from 410 to 626 GPa. To analyze the nature of conductivity, the...     

固体氢的压缩行为

 同时考虑分子的平动与转动自由度，用等温等压系综的路径积分蒙特卡罗方法研究了固体氢的状态方程。在有实验数据的区域，计算结果同实验结果符合很好，在无实验数据的超高压区域，计算结果同实验的外推结果符合。为了定量研究零点运动，还计算了体系的能量。     

Simulation of ab Initio Dynamics of the Formation of Metastable Conducting Solid Hydrogen

Journal of Experimental and Theoretical Physics - Density-functional theory (DFT) is applied to the calculation of the equation of state, the pair correlation function (PCF), and the static...     

Metal-Element-Incorporation Induced Superconducting Hydrogen Clathrate Structure at High Pressure

The recent observation of high critical temperature T_c in lanthanum and Yttrium hydrides confirms the key role of hydrogen cage(H-cage)in determining high superconductivity.Here,we present a new class of metastable H₁₂ clathrate structures based on the icosahedral cI 24-Na that can be stabilized by incorporation of metal elements.Analysis shows that the charge transfer from metal atoms to H atoms contributes to forming the H₁₂ clathrate.Nine dynamically stable structures are identified to exhibit superconductivity,and a maximum T_c of 28K is found in voids-doped Mo₆H₂₄.Calculations reveal that the low T_c is attributed to the weak interaction between H atoms in each cage due to the long H–H distance.The current results provide a possible route to design H-cage containing superconductors.     

High Pressure as a Tool for Characterizing Charge Carriers in a Conducting Polymer

A characteristic feature of conducting polymers is the existence of localized charge carriers. The localization process is closely related to the charge carrier-phonon interaction, which is a function of local molecular properties of the polymer chain on which the carriers are localized. Depending on this interaction in conducting polymers with a non-degenerate ground state singly charged polarons or doubly charged bipolarons may exist. It will be shown that high pressure is a useful tool for studying charge carrier properties by influencing the local molecular conformation. A transition between both types of charge carriers is observed in polypyrrole.     

Infrared Spectra of Liquid and Crystalline Ethanol at High Pressures

Abstract

Mid-infrared spectra in the ranges 400–1800 and 2700–4600 cm^?1 of ethanol samples in diamond anvil cells at ambient temperature and pressures up to 11 GPa are reported. The freezing pressure is confirmed to be 1.8 GPa, and, unlike methanol, the resulting solid is crystalline rather than glassy. No further phase transitions are observed in this pressure range. The wave number shifts of 30 selected peaks with pressure are deduced, and their small magnitudes indicate that only minor distortions of the molecules occur. The effects of the strengthening of the intermolecular hydrogen bonds with pressure on the internal modes are briefly discussed.     

高压下正戊醇的构象和氢键研究

压力是一个重要的物理参量,通过调节物质内部分子、原子间距离和相互作用力,可以引起物质结构和构象变化。正醇是一种最简单的羟基代替烷基链末端氢原子的有机物,通过氢键和烷基链之间的作用力结合在一起,被称为氢键液体。氢键的键能较小,在外部压力作用下,氢键容易被压缩而断裂或网络重排,从而导致晶体结构和对称性的改变,对材料的性能产生重要影响。正戊醇是一种短链正醇,结构虽然简单,却可以作为烷基链结构有机物的典型代表。然而,高压下正戊醇的性质研究较少,尤其压力作用下其构象变化和氢键研究尚未见报道,因此正戊醇高压研究有待进一步深入。拉曼光谱和红外光谱是高压研究中常用的谱学测量技术,能够原位探测压力作用下分子内部基团变化,是研究结构、构象和氢键作用的有效手段。基于此,利用金刚石对顶砧装置(DAC),结合拉曼光谱和红外光谱,在0~12.0 GPa压力范围对正戊醇进行了高压研究。实验结果分三部分讨论:(1)研究了压力作用下正戊醇的结构相变行为。压力在3.2 GPa时,拉曼特征峰变锐变窄,同时有特征峰劈裂和新特征峰出现的现象,说明在该压力点发生一次液固相转变。(2)揭示了正戊醇在高压下的构象变化。正戊醇存在两种构象:反式构象和扭曲构象。通过分析两种构象特征峰随压力的变化,发现正戊醇发生液固相转变的过程伴随有构象变化,液态时以扭曲构象为主,固态时以反式构象为主。(3)探究了高压对正戊醇氢键的影响。羟基的特征峰随压力的增加发生红移,说明在加压过程中氢键作用增强。伴随液固相变,羟基特征峰劈裂成多个峰,形成新的氢键网络或团簇,且随压力的增加氢键网络或团簇逐渐增大,说明氢键对压力非常敏感,且对正戊醇晶体结构的稳定起着促进作用。该研究不仅为正戊醇生产应用提供重要的指导作用,同时为其他同类或复杂分子体系的物理和化学特性研究提供参考。     

X射线衍射法研究不同类型淀粉高静压处理后晶体结构的变化

对300, 450和600 MPa不同高静压力下导致的淀粉结晶结构变化进行研究。选择不同类型、不同链/支比的三种淀粉为研究对象,进行高静压处理,利用X射线衍射法分析高静压对不同类型,不同链/支比淀粉晶体结构的影响。结果表明：由于X射线衍射峰加强及相对结晶度增大,糯玉米淀粉在300 MPa表现为韧化作用,在450 MPa结晶结构完全解体,600 MPa时发生重结晶;HylonⅦ淀粉在600 MPa以下的高静压处理只表现出韧化效果,结晶度增加但不明显;木薯淀粉在300 MPa具有韧化作用,600 MPa结晶结构完全消失,表现为韧化-颗粒结晶解体两个过程。因此,本文提出淀粉颗粒在高静压处理过程中经历压缩韧化-晶体结构解体-重结晶三个发展阶段。     

白硅钙石的高温高压拉曼光谱研究

利用活塞圆筒装置在1.2 GPa,1 473 K的条件下合成了白硅钙石。采用外加热装置和金刚石压腔结合拉曼光谱分析技术,采集了白硅钙石298,353,463,543,663,773以及873 K温度区间的常压及1 atm～14.36 GPa(常温)压力区间的拉曼谱图。扫描电镜下,该研究合成的样品为结构一致的单一相,颗粒大小为10～20 μm。电子探针分析结果表明,样品的组成为Ca_7.03(2)Mg_0.98(2)Si_3.94(2)O₁₆,该组分完全吻合白硅钙石理论组分。Raman分析结果表明,高温时白硅钙石的拉曼谱图中具有29个振动峰。随着温度的升高,部分振动峰出现了合并或者弱化消失的现象。该现象尤其以800～1 200 cm-1范围内的909,927和950 cm-1振动峰峰位最为明显,这些振动峰分别在873,773以及873 K时弱化消失。据此,白硅钙石的结构在实验温压范围内稳定,且随着温度和压力的升高,其拉曼振动峰峰位分别呈现往低频和高频方向线性飘移的趋势。除此之外,根据高温和高压拉曼实验的结果,分别计算了白硅钙石拉曼振动峰峰位的等压mode-Grüneisen参数和等温mode-Grüneisen参数,其算术平均值分别为1.47(2)和0.45(3)。最后结合高温和高压拉曼实验的结果,计算了白硅钙石的非谐系数,结果表明,Si-O振动模式对于非谐效应的贡献要小于其他振动模式。     

高温高压下绿辉石成因研究

在3 GPa,1 200 ℃条件下,分别以碱性玄武岩粉末和等化学计量光谱纯试剂为原料进行高温高压熔融结晶实验,对实验产物进行了电子探针测试和拉曼光谱分析,确定结晶产物为绿辉石,其拉曼谱峰的半高宽较窄且形态尖锐,表明绿辉石晶体中Si—O四面体结构稳定,矿物内部有序度高。结合前人研究成果探讨了绿辉石成因的影响因素及其原始岩浆,结果表明绿辉石的形成可能受母岩成分、体系流体含量和温压条件等多种因素影响。本实验结果为绿辉石和榴辉岩成因学研究提供可能的实验依据。     

Thermodynamic Description of Crystalline Water Phases Containing Hydrogen

JETP Letters - Stability regions of crystal phases in the water–hydrogen system have been studied within our statistical thermodynamic model for describing clathrate compounds. The...     

Infrared Spectra of Crystalline,Glassy and Liquid Methanol at High Pressures

Abstract

Mid-infrared spectra in the range 400–1800 cm^?1 of methanol samples in diamond anvil cells at ambient temperature and pressures up to 11 GPa are reported. The freezing pressure is confirmed to be 3.6 GPa, and the spectra of the resulting metastable glass are very similar to those of the liquid. When maintained at high pressure, the glass spontaneously transforms to an ordered crystalline phase which is stable over the range 3.6 to 11 GPa. Small changes in peak wavenumbers for 14 internal modes as a function of pressure are observed, indicating that distortion of the molecules is minimal. A slight decrease for the C-O-H bending mode is attributed to charge transfer from the molecular 0-H bond to the strengthening intermolecular hydrogen bond.     

金刚石压腔高温高压实验的压力标定方法及其现状

 介绍和评论了金刚石压腔中进行高温高压实验时的压力标定方法及其应用条件。其中红宝石和石英压标具有较高的准确度和精度,但前者不适合于高温和含饱和水条件下的标定,且在较低压力下误差较大,后者可用于高温且含水体系的压力标定,但仅适于低于2.0 GPa时的压力标定。矿物状态方程是较可靠的方法,但不方便且受条件限制。采用水的状态方程进行压力标定,可以解决压腔中不允许有压标矿物的问题,但在实验过程中要求压腔的体积保持恒定。因此,在采用金刚石压腔进行高温高压实验时,应根据研究需要决定合适的压力标定方法,而且寻找新的压力标定方法仍是金刚石压腔高压实验的基础工作。     

Structural Investigation of Solid Methane at High Pressure

High pressure studies of solid methane are performed using both classical simulated annealing and first-principles methods. A series of simulated annealing and geometry optimization reveal a monoclinic P21/b structure with the unit cell containing four methane molecules. The phonon dispersion curves and vibrational density of states indicate that this structure is stable in the pressure range 10-90 GPa. The electronic band structure and density of states show that this structure has not metalized until 90 GPa.     

Superconductivity Observed in Tantalum Polyhydride at High Pressure

We report experimental discovery of tantalum polyhydride superconductor.It was synthesized under highpressure and high-temperature conditions using diamond anvil cell combined with in situ high-pressure laser heating techniques.The superconductivity was investigated via resistance measurements at pressures.The highest superconducting transition temperature T_c was found to be ～30 K at 197 GPa in the sample that was synthesized at the same pressure with ～2000 K heating.The transitions a...     

低温相HI分子晶体振动光谱计算

低温相ＨＩ分子晶体振动光谱计算毛延哲曾维扬（兰州大学物理系兰州７３００００）ＣａｌｃｕｌａｔｉｏｎｏｆｔｈｅＶｉｂｒａｔｉｏｎａｌＳｐｅｃｔｒｏｓｃｏｐｙｏｆＣｒｙｓｔａｌｉｎｅＨｙｄｒｏｇｅｎＩｏｄｉｄｅＭａｏＹａｎｚｈｅ（Ｄｅｐｔ．ｏｆｆｕｎｄ...