Superhard monoclinic BN allotrope in M-carbon structure

Superhard materials have always attracted people's interesting due to their extensive industrial applications. In this work, two reasonable superhard monoclinic allotropes of boron nitrides with space group of Cm have been designed based on previously proposed M-carbon structure using first-principles calculations. Our results show that Cm-BN-1 and Cm-BN-2 are dynamically stable, and they are direct semiconductors with bandgap of 2.69 and 3.90 eV, respectively. Moreover, they could be potential superhard materials with Vickers hardness of 58.0 and 60.4 GPa, respectively. This work provides insights for exploring new superhard boron nitrides materials.     

Re_3N的变温拉曼散射与高压同步辐射研究

本工作通过高压固相复分解反应(HPSSM)合成块体Re_3N。利用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)和能量色散X射线分析(EDS)对高压样品进行结构表征与元素成分确定,结果表明利用HPSSM法合成的Re_3N具有较高的晶体质量。在77K到873K温度范围内利用拉曼散射研究Re_3N的晶格振动特性。基于三(四)声子耦合模型,研究Re_3N拉曼声子模频率的红移和拉曼峰的宽化现象,结果表明高温条件下Re_3N拉曼散射效应中三声子耦合过程占主导。高压同步辐射研究表明Re_3N具有很高的体弹模量(B0=417GPa),是一种潜在的超硬材料。     

Toroid type high-pressure device: history and prospects

The Toroid type high-pressure device and its predecessor, the Chechevitsa (lentil) type high-pressure device, are known to be used efficiently for the synthesis of new materials in recent decades. It was through the Chechevitsa device the first ultradense modification of silica, ‘stishovite’, was obtained. Both devices were essential for the industrial production of superhard materials in the USSR and other socialist countries. In 1980s, almost half of the world synthetic diamond and c-BN products were manufactured by these devices. However, the application of the Toroid device for examining the structure and physical properties of highly compressed substances has been considerably less appreciated. Meanwhile, the device has some unique features that have made possible 35-years of an extensive investigation of physical properties of substances at pressures up to 150 kbar, including electron transport and thermodynamic properties, elastic characteristics, viscosity, thermo-conductivity and other physical properties. Also, the device has been widely employed for structural X-ray and neutron diffraction studies of many materials. But it is not until recently that the convenience of the Toroid device for physical studies has been fully recognized. Through this recognition, the Toroid type device is today becoming increasingly popular among the researchers in the field of high pressures around the world.     

Progress in functional studies of transition metal borides

In recent years, transition metal borides (TMBs) have attracted much attention because they are considered as potential superhard materials and have more abundant crystal structures compared with traditional superhard materials. So far, however, no superhard materials have been found in TMBs. A large number of structures and potential new properties in TMBs are induced by the various hybridization ways of boron atoms and the high valence electrons of transition metals, which provide many possibilities for its application. And most TMBs have layered structures, which make TMBs have the potential to be a two-dimensional (2D) material. The 2D materials have novel properties, but the research on 2D TMBs is still nearly blank. In this paper, the research progress of TMBs is summarized involving structure, mechanical properties, and multifunctional properties. The strong covalent bonds of boron atoms in TMBs can form one-dimensional, two-dimensional, and three-dimensional substructures, and the multiple electron transfer between transition metal and boron leads to a variety of chemical bonds in TMBs, which are the keys to obtain high hardness and multifunctional properties of TMBs. Further research on the multifunctional properties of TMBs, such as superconductors, catalysts, and high hardness ferromagnetic materials, is of great significance to the discovery of new multifunctional hard materials.     

Synthesis of novel transition metal nitrides IrN2 and OsN2

Two new transition metal nitrides, IrN2 and OsN2, were synthesized at high pressures and temperatures using laser-heated diamond-anvil cell techniques. Synchrotron x-ray diffraction was used to determine the structures of novel nitrides and the equations of states of both the parent metals as well as the newly synthesized materials. The compounds have bulk moduli comparable with those of the traditional superhard materials. For IrN2, the measured bulk modulus [K0 = 428(12) GPa] is second only to that of diamond (K0 = 440 GPa). Ab initio calculations indicate that both compounds have a metal:nitrogen stoichiometry of 1:2 and that nitrogen intercalates in the lattice of the parent metal in the form of single-bonded N-N units.     

A new family of sp~3-hybridized carbon phases

A new family of superhard carbon allotropes C48(2i + 1) is constructed by alternating even 4 and 8 membered rings.These new carbon allotropes are of a spatially antisymmetrical structure, compared with the symmetrical structures of bctC4, Z-carbon, and P-carbon. Our calculations show that bulk moduli of C48(2i + 1) are larger than that of c-BN and smaller than that of cubic-diamond. C48(2i + 1) are transparent superhard materials possessing large Vicker hardness comparable to diamond. This work can help us understand the structural phase transformations of cold-compression graphite and carbon nanotubes.     

强冲击压缩条件下g-C3N4向β-C3N4直接转化

 为了合成出理论预言的具有致密结构的超硬材料C₃N₄,运用二级轻气炮加载和冲击回收实验技术,以富含N的g-C₃N₄为前驱物,在40~65 GPa压力下完成了冲击合成实验。在低于51 GPa压力时,X射线衍射分析表明,在回收样品中未发现有新相生成,说明g-C₃N₄是稳定的;而在51~65 GPa范围内,回收样品中有新相生成,与理论计算结果对照发现,新相为β-C₃N₄相,且不含其它结晶相。证实利用冲击合成方法将g-C₃N₄直接转化为单纯β-C₃N₄是可能的,对纯净的超硬相碳氮化合物的合成研究具有参考意义。     

High-pressure route to superhard boron-rich solids

Novel superhard phases are expected to be found among various high-pressure polymorphs of light element compounds. Besides diamond-like phases, the icosahedral boron-rich solids are of particular interest because they could combine high hardness with advanced electronic and phonon transport properties, lightness, high thermal and chemical stability. Here we review some recent results on high-pressure synthesis of novel boron-rich solids.     

Electronegativity identification of novel superhard materials

We show that electronegativity can be used to effectively identify the hardness of crystal materials on the basis of a new microscopic model for hardness. Bond electronegativity is proposed to characterize the electron-holding energy of a bond, which is the intrinsic origin of hardness. Applying this model to c-BC(2)N materials, we confirm the proper bond composition of the experimentally observed phase of c-BC(2)N, in which the bond ratio N(C-C):N(B-N):N(B-C):N(C-N) is 3:3:1:1. A number of bonds that can or cannot form a superhard material are qualitatively distinguished, which enables us to explore novel superhard materials by screening possible elemental combinations.     

Structural stability at high pressure,electronic, and magnetic properties of BaFZnAs:A new candidate of host material of diluted magnetic semiconductors

The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized.Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measurements demonstrate that the structure of BaFZnAs is stable under pressure up to 17.5 GPa at room temperature. The resistivity and the magnetic susceptibility data show that BaFZnAs is a non-magnetic semiconductor. BaFZnAs is recommended as a candidate of the host material of diluted magnetic semiconductor.     

过渡金属化合物OsB2与OsO2低压缩性的第一性原理计算研究

利用基于密度泛函理论平面波赝势法的第一性原理计算,研究了过渡金属化合物OsB2和OsO2的金红石相、黄铁矿相与萤石相三种结构在高压下的状态方程和结构特性以及OsO2可能的高压相变.理论计算结果支持OsB2与OsO2的萤石相是潜在超低可压缩性的硬性材料.同时,也分析了它们的电子结构,力求理解大体变模量和高硬度的微观机制.结果表明,可以利用过渡金属高的价电子浓度,掺入硼、氧、碳、氮等轻的元素形成强的方向键,这可能提供了一种合成超硬材料的新途径.     

Pressure- and temperature-induced transformations in crystalline polymers of C60

The great advantage of the C₆₀ molecule is its potential for polymerization, due to which the molecule can be the building block of new all carbon materials. In addition, it contains, both sp ² and sp ³ hybridized carbon atoms, which allows synthesizing new carbon materials with desired physicochemical properties using both types of carbon bonding. The one- and two-dimensional polymeric phases of C₆₀ are prototype materials of this sort. Their properties, especially polymerization under pressure and room temperature via covalent bonding between molecules belonging to adjacent polymeric chains or polymeric layers, can be used for further development of new materials. The present review focuses on the study of the pressure-induced polymerization and thermodynamic stability of these materials and their recovered new phases by in-situ high-pressure Raman and X-ray diffraction studies. The phonon spectra show that the fullerene molecular cage in the high-pressure phases is preserved, while these polymers decompose under heat treatment into the initial fullerene C₆₀ monomer.     

Deformation‐induced bonding evolution of iron tetraboride and its electronic origin

First‐principles density functional calculations are employed to provide a fundamental understanding of the structural features, mechanical properties, deformation behaviours and its electronic origin for the new synthesized FeB₄. The calculated elastic moduli suggest that FeB₄ has a low compressibility, but results of ideal shear strength and theoretical hardness indicate that FeB₄ is a hard material, not a superhard material. We find that the collapse of the unique corrugated B₆ units ring in FeB₄ under deformation is responsible for the failure under tensile and shear deformation based on the calculated charge density distribution and bonding evolution. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Kinetics of phase transitions under high pressure

Abstract

Phase transitions under high pressure have attracted increasing attention i n connection with high pressure synthesis of new materials (e.g. superhard materials, ceramics, semiconductors, high temperature superconductors) and the exploration of geological processes like the formation of rocks and minerals. For t h e investigation of thermodynamic and electronic equilibrium properties a broad spectrum of methods for pressure generation and physical measurements have been developed ^1,2,3,4. Tha measurement of equilibrium properties, however, gives only poor insight into the detailed mechanisnts of phase changes. The accurate determination of phase equilibria and phase diagrams becomes inore and more difficult a t low temperatures due to increasing hysteresis effects end t h e extrapolation of experimental data to zerc, teiiipwature a nd the compar ison with quantumiiiechanical ah in.itio calculations are questionable.     

Elastic moduli of nc-TiN/a-Si3N4 nanocomposites: Compressible, yet superhard

Earlier measurements of elastic moduli of nc-TiN/a-Si₃N₄ nanocomposites of different composition and hardness by means of vibrating reed and surface Brillouing scattering, that yield Young’s and shear modulus, as well as the Poisson’s ratio, have been confirmed by high-pressure X-ray diffraction measurements, that yield bulk modulus. It is found that elastic moduli of all measured samples are essentially the same within relatively small error of measurements, and only slightly lower than that of pure TiN. The nanocomposites are superhard thanks to their unique nanostructure with strengthened SiN_x interface.     

高压下低维材料的光学特性调控

压力作为独立于物质温度和组分的热力学参量,为物质科学的研究和创新提供了新的维度,已成为发展新概念、创造新理论及探索新材料的重要源泉。本文主要概述了作者近年来在高压下低维材料的光学特性调控方面所取得的一些进展。通过压力改变激子结合能和卤素八面体的扭曲行为,实现了低维卤化物钙钛矿纳米材料发光从“0”到“1”的突破,提出了压力诱导发光的概念;通过引入压力效应,利用压力对纳米材料表面配体的调控,改变了表面配体与CdSe量子点的相互作用和能级耦合,促进了Hirshfeld电荷转移,从而实现了CdSe量子点的荧光大幅度增强近一个数量级;借助高压手段调控能带结构,成功实现了CdSe/CdS半导体纳米晶由准Ⅱ型核壳结构向Ⅰ型核壳结构的构型转变。上述工作加深了对发光材料在极端压缩条件下构效关系的深入理解和认识,研究成果为设计和制备具有特定功能的低维材料提供了新方法。     

Solvated fullerenes,a new class of carbon materials suitable for high-pressure studies: A review

As the list of known carbon compounds grows longer, solvated fullerenes have become a more important class of carbon materials. Their general properties and methods of synthesis have both attracted considerable attention. The study of the behavior of these compounds under high-pressure conditions has revealed several new phenomena that have never been observed in pure fullerene. This article is a review of all recent progress in this field.     

新型圆角式高压碳化钨硬质合金顶锤的有限元分析

基于有限元法, 对新型圆角式高压碳化钨硬质合金顶锤进行了分析与研究.研究结果表明: 新型圆角式高压碳化钨硬质合金顶锤在不降低顶锤的传压效率的前提下, 能够将顶锤的使用寿命延长3.05%—16.75 %; 新型圆角式高压碳化钨硬质合金顶锤获得的极限腔体压力值可增加至6.09 GPa, 较传统顶锤(5.80 GPa)提高5%, 从而扩宽高压下功能材料的合成区间.新型圆角式高压碳化钨硬质合金顶锤的使用, 将降低六面顶液压机的使用成本, 促进高压技术和材料科学等学科的发展.     

Prediction of a superhard material of ReN4 with a high shear modulus

Using first-principles calculations, this paper systematically investigates the structural, elastic, and electronic properties of ReN 4 . The calculated positive eigenvalues of the elastic constant matrix show that the orthorhombic P bca structure of ReN 4 is elastically stable. The calculated band structure indicates that ReN 4 is metallic. Compared with the synthesized superhard material WB 4 , it finds that ReN 4 exhibits larger bulk and shear moduli as well as a smaller Poisson’s ratio. In addition, the elastic constant c 44 of ReN 4 is larger than all the known 5d transition metal nitrides and borides. This combination of properties makes it an ideal candidate for a superhard material.     

New superhard phases for three-dimensional C60-based fullerites

We have explored new possible phases of 3D C60-based fullerites using semiempirical potentials and ab initio density functional methods. We have found three closely related structures-two body-centered orthorhombic and one body-centered cubic-having 52, 56, and 60 tetracoordinated atoms per molecule. These 3D polymers result in semiconductors with bulk moduli near 300 GPa, and shear moduli around 240 GPa, which make them good candidates for new low density superhard materials.