다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Pressure is a fundamental thermodynamic variable that can be used to control the properties of materials, because it reduces interatomic distances and profoundly modifies electronic orbitals and bonding patterns. It is thus a versatile tool for the creation of exotic materials not accessible at ambient conditions. Recently developed static and dynamic high-pressure experimental techniques have led to the synthesis of many functional materials with excellent performance: for example, superconductors, superhard materials and high-energy-density materials. Some of these advances have been aided and accelerated by first-principles crystal-structure searching simulations. In this Review, we discuss recent progress in high-pressure materials discovery, placing particular emphasis on the record high-temperature superconductivity in hydrogen sulfide and on nanotwinned cubic boron nitride and diamond, the hardest known materials. Energy materials and exotic chemical materials obtained under high pressures are also discussed. The main drawback of high-pressure materials is their destabilization after pressure release; this problem and its possible solutions are surveyed in the conclusions, which also provide an outlook on the future developments in the field. High pressure offers a unique degree of freedom for the creation of new materials, leading to new superconductors, superhard materials, high-energy-density materials and exotic chemical materials with unprecedented properties. This Review discusses these materials, along with recently developed theoretical and experimental methods for materials discovery at high pressures.

Materials discovery at high pressures

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Projector-Augmented Wave Method: An introduction

The search for stable polymeric nitrogen and polynitrogen compounds has attracted great attention due to their potential applications as high-energy-density materials. Here we report a theoretical prediction of an interesting LiN5 crystal through first-principles calculations and unbiased structure searching techniques. Theoretical calculations reveal that crystalline LiN5 is thermodynamically stable at pressures above 9.9 GPa, and remains metastable at ambient conditions. The metastability of LiN5 stems from the inherent stability of the N5– anions and strong anion–cation interactions. It is therefore possible to synthesize LiN5 by compressing solid LiN3 and N2 gas under high pressure and quench recover the product to ambient conditions. To the best of our knowledge, this is the first time that stable N5– anions are predicted in crystalline states. The weight ratio of nitrogen in LiN5 is nearly 91%, placing LiN5 as a promising high-energy material. The decomposition of LiN5 is expected to be highly exoth...

Crystalline LiN5 Predicted from First-Principles as a Possible High-Energy Material

Elastic and electronic properties of Pbca-BN: First-principles calculations

Structural, mechanical, and electronic properties of P3m1-BCN

The pressure-induced formation of a hexagonal phase (P6/m, Z = 2) of LiN3 is predicted by particle swarm optimization (PSO) structural search at zero temperature and pressure of > 34.7GPa. Compared to the ground-state insulator C2/m phase, the P6/m-LiN3 is found to possess a metallic feature dominated by the 2p(z) bands. Electron topological analysis revealed an intriguing phase change of nitrogen, from azide to novel pseudo-benzene "N-6" molecules at the formation of the P6/m phase. The occurrence of this hexagonal phase follows the polymerization of the typical linear N-3(-) anion molecular chains in the low-pressure molecular phases of LiN3 and is originated from the volume reduction favorable for a denser structure packing under compression. Copyright (C) EPLA, 2013

https://iopscience.iop.org/article/10.1209/0295-5075/101/26004/pdf

Novel high-pressure phase with pseudo-benzene “N6” molecule of LiN3

A novel superhard carbon allotrope C64 is predicted which is composed of C28 cages. It is porous and exhibits distinct topologies including zigzag 5, 6, 8, 10 and 12-fold carbon rings. The elastic constants and phonon calculations reveal that C64 is mechanically and dynamically stable at ambient pressure. The hardness of C64 is 60.2 GPa. The tensile and shear strength calculations indicate that the lowest tensile and shear strengths have the almost same value of 48.1 GPa. For the electronic properties, the band structure calculations show that C64 is a quasi-direct band gap semiconductor with a band gap of 1.32 eV.

A new superhard carbon allotrope: tetragonal C64

http://web.xidian.edu.cn/qunwei/files/20110731_220845.pdf

Haiyan Yan

Papers

Elastic and electronic properties of Pbca-BN: First-principles calculations

Structural, mechanical, and electronic properties of P3m1-BCN

Novel high-pressure phase with pseudo-benzene “N6” molecule of LiN3

A new superhard carbon allotrope: tetragonal C64

A first-principle calculation of structural, mechanical and electronic properties of titanium borides