Theoretical design of diamondlike superhard structures at high pressure

Diamond, as the hardest known material, has been widely used in industrial applications as abrasives, coatings, and cutting and polishing tools, but it is restricted by several shortcomings, e.g., its low thermal and chemical stability. Considerable efforts have been devoted to designing or synthesizing the diamond-like B-C-N-O compounds, which exhibit excellent mechanical property. In this paper, we review the recent theoretical design of diamond-like superhard structures at high pressure. In particular, the recently designed high symmetric phase of low-energy cubic BC3 meets the experimental observation, and clarifies the actual existence of cubic symmetric phase for the compounds formed by B-C-N-O system,besides the classical example of cubic boron nitride.

In-situ high pressure X-ray diffraction studies of orthoferrite SmFeO_3

The high-pressure behaviors of SmFeO3 are investigated by angle-dispersive synchrotron X-ray powder diffraction under a pressure of up to 40.3 GPa at room temperature. The crystal structure of SmFeO3 remains stable at up to the highest pressure. The different pressure coefficients of the normalized axial compressibility are obtained to be βa = 0.60 × 10-3 GPa-1,βb = 0.79 × 10-3 GPa-1, βc = 1.28 × 10-3 GPa- 1, and the bulk modulus （B0） is determined to be 293（3） GPa by fitting the pressure-volume data using the Birch-Murnaghan equation of state. Furthermore, the larger compressibility of the FeO6 octahedra suggests the evolution of the orthorhombic structure towards higher symmetry configuration at high pressures.

Structural and electrical transport properties of Dirac-like semimetal PdSn4 under high pressure

We conducted in-situ high-pressure synchrotron x-ray diffraction(XRD) and electrical transport measurements on Dirac-like semimetal Pd Sn4 in diamond anvil cells with quasi-hydrostatic pressure condition up to 44.5 GPa–52.0 GPa. The XRD data show that the ambient orthorhombic phase(Ccca) is stable with pressures to 44.5 GPa, and the lattice parameters and unit-cell volume decrease monotonously upon compression. The temperature dependence of the resistance exhibits a metallic conduction and follows a Fermi-liquid behavior below 50 K, both of which keep unchanged upon compression to 52.0 GPa. The magnetoresistance curve at 5 K maintains a linear feature in a magnetic field range of 2.5 T–7 T with increasing pressure to 20.0 GPa. Our results may provide pressure-transport constraints on the robustness of the Dirac fermions.

Structural evolution and molecular dissociation of H_(2)S under high pressures

Solid H_(2)S as the precursor for H_(3)S with incredible superconducting properties under high pressure,has recently attracted extensive attention.Here in this work,we propose two new phases of H_(2)S with P42/n and I41/a lattice symmetries in a pressure range of 0 GPa–30 GPa through first-principles structural searches,which complement the phase transition sequence.Further an ab initio molecular dynamics simulation confirms that the molecular phase P2/c of H_(2)S is gradually dissociated with the pressure increasing and reconstructs into a new P2_(1)/m structure at 160 GPa,exhibiting the superconductivity with Tc of 82.5 K.Our results may provide a guidance for the theoretical study of low-temperature superconducting phase of H_(2)S.

Structural and electrical transport properties of charge density wave material LaAgSb_(2)under high pressure

Layered lanthanum silver antimonide LaAgSb_(2)exhibits both charge density wave(CDW)order and Dirac-cone-like band structure at ambient pressure.Here,we systematically investigate the pressure evolution of structural and electronic properties of LaAgSb_(2)single crystal.We show that the CDW order is destabilized under compression,as evidenced by the gradual suppression of magnetoresistance.At P_(C)~22 GPa,synchrotron x-ray diffraction and Raman scattering measurements reveal a structural modification at room-temperature.Meanwhile,the sign change of the Hall coefficient is observed at 5 K.Our results demonstrate the tunability of CDW order in the pressurized LaAgSb_(2)single crystal,which can be helpful for its potential applications in the next-generation devices.

The Zinc Story under High Pressure

A historical review is presented on the experimental and theoretical studies on Zn under high pressure. Based on our high-pressure powder x-ray diffraction experiments that have been done for nearly a decade, we describe the structural change of Zn up to 126 GPa at room temperature. Although several experimental and theoretical studies indicated an anomalous change of the c/a axial ratio with pressure, we found no such an anomaly within our experimental uncertainty. Our high-pressure low-temperature experiments up to 18 GPa at 40 K also gave no evidence of the c/a anomaly. We suspect that the pressure-transmitting media played an important role in producing the anomaly. The structural anisotropy of Zn is drastically reduced at high pressures, which would be a general trend for hexagonal close-packed (hcp) metals.

High-pressure-activated carbon tetrachloride decomposition

The pressure-induced molecular dissociation as one of the fundamental problems in physical sciences has aroused many theoretical and experimental studies. Here, using a newly developed particle swarm optimization algorithm, we investigate the high-pressure-induced molecular dissociation. The results show that the carbon tetrachloride （CC14） is unstable and dissociates into C2C16 and C12 under approximately 120 GPa and more. The dissociation is confirmed by the lattice dynamic calculations and electronic structure of the Pa3 structure with pressure evolution. The dissociation pressure is far larger than that in the case of high temperature, indicating that the temperature effectively reduces the activation barrier of the dissociation reaction of CC14. This research improves the understanding of the dissociation reactions of CC14 and other halogen compounds under high pressures.

In-situ high-pressure behaviors of double-perovskite Sr_2ZnTeO_6

Structural and spectroscopic properties of Sr2ZnTeO6 （SZTO） were investigated by angle-dispersive synchrotron X- ray powder diffraction and Raman spectroscopy in a diamond anvil cell up to 31 GPa at room temperature. Although SZTO remained stable up to the highest pressure, the different pressure coefficients of the normalized axial compressibility were obtained as βab=8.16×10-3 GPa-1 andβc=7.61 x 10-3 GPa-1. The bulk modulus B0 was determined to be 190（1） GPa by fitting the pressure-volume data using the Birch-Mumaghan equation of state. All the observed Raman modes exhibited a broadening effect under high pressure. The vibrational band V1 around 765 cm-1, which is associated with the Te-O stretching mode in the basal plane of the TeO6 octahedron had the largest pressure coefficient, and the Griineisen parameters for all the observed phonon modes were also calculated and presented. These parameters could be used to measure the amount of uniaxial or biaxial strain, providing a fundamental tool for monitoring the magnitude of the shift of phonon frequencies with strains.

Theoretical study of BTF/TNA cocrystal: Effects of hydrostatic pressure and temperature

Cocrystallization is a promising technique for the design and preparation of new explosives,and the stability of cocrystal is highly concerned by the researchers.In order to make a better understanding of the behavior of cocrystal under the extreme conditions,DFT(density functional theory) calculation is performed to investigate the effect of hydrostatic pressure on geometrical and electronic structures of the cocrystal BTF(benzotrifuroxan)/TNA(2,4,6-trinitroaniline).When the hydrostatic pressure is applied,the lattice constants,volume,density and total energy change gradually except at the pressures of 40 GPa and 79e83 GPa.It is noteworthy that new chemical bonds form when the pressure is up to83 GPa.The band gap of the cocrystal becomes smaller when the pressure is applied,and finally the cocrystal shows a characteristic of metal.The mechanical property of cocrystal is calculated by MD(molecular dynamics) simulation.The results show that the cocrystal has a better ductibility at low temperature,and has the best tenacity at 295 K.

New carbon-nitrogen-oxygen compounds as high energy density materials

Molecular crystals are complex systems exhibiting various crystal structures,and accurately modeling the crystal structures is essential for understanding their physical behaviors under high pressure.Here,we perform an extensive structure search of ternary carbon-nitrogen-oxygen(CNO)compound under high pressure with the CALYPSO method and first principles calculations,and successfully identify three polymeric CNO compounds with Pbam,C2/m and I4m2symmetries under 100 GPa.More interestingly,these structures are also dynamically stable at ambient pressure,and are potential high energy density materials(HEDMs).The energy densities of Pbam,C2/m and I4m2 phases of CNO are about2.30 kJ/g,1.37 kJ/g and 2.70 kJ/g,respectively,with the decompositions of graphitic carbon and molecular carbon dioxide andα-N(molecular N_(2))at ambient pressure.The present results provide in-depth insights into the structural evolution and physical properties of CNO compounds under high pressures,which offer crucial insights for designs and syntheses of novel HEDMs.

尼龙-1010结晶结构

用WAXD方法测定了Nylon-1010为三斜晶系结晶结构;α=4.9(?),b=5.4(?),c=27.8(?),α=49°,β=77°,γ=63.5°,每个聚合物单胞含有一个重复单元,空间群为P(?)。模压试样用Ruland方法分析结晶度为60％。以上。电子密度相关函数法分析了SAXS现象,求得了Nylon-1010结晶片层厚度、过渡层厚度、长周期、比内表面及电子密度差。

压力对尼龙1010凝聚态结构的影响

研究了尼龙(PA)1010在250℃、不同压力下退火30 min后凝聚态结构的变化。结果表明,在压力小于1.0 GPa和大于1.2 GPa的范围内,PA1010室温结晶的三斜晶系的晶体结构没有变化,但是(100)晶面的衍射强度随压力的增加而减弱,而(110/010)晶面的衍射强度增加;当压力在1.0～1.2 GPa时,PA1010的X射线衍射图谱没有明显的衍射峰,DSC和溶解实验证实,PA1010在该压力范围内发生了交联,并进一步讨论了PA1010在高压下发生交联的机理。

尼龙1010骤冷退火样品的晶体结构

尼龙1010的晶体结构属三斜晶系.作者最近导出了X射线衍射法（WAXD）测定尼龙1010结晶度的公式,进而考查了等温结晶时结晶温度TC对结晶度XC、晶粒尺寸L100和氢键面相对衍射强度R的影响.发现XC和L100均随TC升高而增大,达196℃后又减小;而R与TC的关系则相反,呈线性降低.结晶速率快有利于分子链在垂直于氢键面的（100）晶面生长,但R值却降低了.本文利用WAXD考查了尼龙1010不同骤冷退火条件样品的晶体结构.

高压下Th_(2)N_(2)S的结构相变:第一性原理计算研究

基于第一性原理计算和粒子群优化算法,研究了Th_(2)N_(2)S在0~200 GPa压强范围内的晶体结构和物理性质.研究结果成功再现了常压下的实验相:P3m1相,同时预测了2个高压下的新结构,即I4/mmm相和Cmmm相.确定了一系列由压强诱导的结构相变序列:由P3m1.相转变为I4/mmm相,然后转变为Cmmm,相应的相变压强分别为4.8.2 GPa和156.2 GPa.Th_(2)N_(2)S材料声子色散曲线及弹性常数的.结果表明,Th_(2)N_(2)S的3相是动力学和力学稳定的.力学性质的计算结果表明,P3m1相、I4/mmm相和Cmmm相均为韧性材料,其中,Cmmm相的各向异性程度是3相中最大的.电子结构的计算表明,P3m1相到I4/mmm相的相变是一个半导体-金属相变.

磷及磷化物高压结构与性能研究进展

磷作为第五主族非金属元素,具有独特的电子结构和优异的光、电、力学等特性,展现出广泛的应用前景。近年来,研究表明磷及磷化物具有极易受到外场影响和调控的特点,且在高压条件下具有丰富的物理化学性质。此外,磷及磷化物的独特结构和电子性质使其具有许多不同于传统材料的物理特性。因此,利用高压在磷和磷化物中实现结构转变、超导转变,已然成为高压领域的研究热点。本文以黑磷、锗磷和砷磷等多种典型的磷和磷化物为例,概述了磷和磷化物在高压调控下的结构、电学、光学等方面的响应,讨论其结构与物理性质之间的构效关系,并对未来在高压下磷化物的研究进行展望。

过渡金属钙钛矿的高压高温合成及物性

过渡金属钙钛矿材料由于具有灵活多变的晶体结构和丰富多样的物理性质,在信息、能源和催化等领域具有广阔的应用前景。然而,在常规条件下合成的过渡金属钙钛矿种类有限。高压作为一种独特的实验手段,能够显著调控材料的原子间距和元素构型,在合成新型钙钛矿材料方面具有较大优势,通过改变电子结构可引发铁电、磁性、超导、金属-绝缘体转变、电荷转移及电荷歧化等新奇的物理性质。本文回顾了极端高压材料制备技术和高压原位测量技术,并对这2项技术在几类过渡金属钙钛矿合成与物性调控方面的应用进行了展望。

钙钛矿氧化物BaMO_(3)(M为过渡金属)的晶体结构和物理性质

钙钛矿氧化物BaMO_(3)(M为过渡族金属)具有复杂的晶体结构和物理性质,本文系统地总结了BaMO_(3)的研究进展,重点关注在M元素变化过程中晶体结构和物理性质的演化,以及高压调控下的结构相变、电输运性质和磁学性质的变化,讨论了M离子半径及合成压力对六方钙钛矿到钙钛矿演化过程的影响,同时对该领域中一些问题做了展望,探讨了这一体系可能出现的新的原子组合和结构,相应材料可能具有的新特性和科学意义。

高压极端条件下的富氢高温超导体

自从在汞中发现4.2 K的超导转变温度以来,寻找室温超导体一直是凝聚态物理领域的研究热点。近年来,科学家在高压极端条件下发现了以共价型H_(3)S(T_(c)=203 K)和离子型LaH_(10)(T_(c)=250 K)、CaH_(6)(T_(c)=215 K)为代表的系列高温超导体,先后刷新了超导转变温度纪录,这些工作开启了学界在富氢化合物中寻找室温超导体的新篇章。本文重点介绍了目前高压下二元和三元富氢高温超导体的理论模拟以及实验制备和表征方面的相关研究进展,分析在富氢化合物中发现室温超导体面临的挑战和可能途径,为实现室温超导做出基础性贡献。

压力下超导RbBSi化合物的预测(英文)

对RbBSi化合物在0~100 GPa压力范围内进行了广泛的群体智能结构搜索。提出了RbBSi的3种不同相,并通过第一性原理计算了其稳定性、电子结构和潜在的超导电性。在所研究的压力范围内,所有预测相在热力学和动力学上都是稳定的。3个相的能带都穿过费米能级,表明结构具备金属性。此外,P4/nmm-RbBSi在常压下的超导转变温度为14.4 K。这项工作加深了人们对碱金属硼硅化合物在超导体领域的理解,有望拓宽碱金属硼硅化合物在超导体领域的应用。

Pressure-induced anomalous insulating behavior in frustrated iridate La_(3)Ir_(3)O_(11)

The geometrically frustrated iridate La_(3)Ir_(3)O_(11) with strong spin–orbit coupling and fractional valence was recently predicted to be a quantum spin liquid candidate at ambient conditions. Here, we systematically investigate the evolution of structural and electronic properties of La_(3)Ir_(3)O_(11) under high pressure. Electrical transport measurements reveal an abnormal insulating behavior rather than metallization above a critical pressure P_(c) ~ 38.7 GPa. Synchrotron x-ray diffraction(XRD)experiments indicate the stability of the pristine cubic KSbO_(3)-type structure up to 73.1 GPa. Nevertheless, when the pressure gradually increases across P_(c), the bulk modulus gets enhanced and the pressure dependence of bond length d_(Ir-Ir) undergoes a slope change. Consistent with the XRD data, detailed analyses of Raman spectra reveal an abnormal redshift of Raman mode and a change of Raman intensity around P_(c). Our results demonstrate that the pressure-induced insulating behavior in La_(3)Ir_(3)O_(11) can be assigned to the structural modification, such as the distortion of IrO_6 octahedra. These findings will shed light on the emergent abnormal insulating behavior in other 5 d iridates reported recently.