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High Pressure Physics and Materials Science|34 Article(s)
A fresh class of superconducting and hard pentaborides
Hui Xie, Hong Wang, Fang Qin, Wei Han, Suxin Wang, Youchun Wang, Fubo Tian, and Defang Duan
On the basis of the current theoretical understanding of boron-based hard superconductors under ambient conditions, numerous studies have been conducted with the aim of developing superconducting materials with favorable mechanical properties using boron-rich compounds. In this paper, first-principles calculations reveal the existence of an unprecedented family of tetragonal pentaborides MB5 (M = Na, K, Rb, Ca, Sr, Ba, Sc, and Y), comprising B20 cages and centered metal atoms acting as stabilizers and electron donors to the boron sublattice. These compounds exhibit both superconductivity and high hardness, with the maximum superconducting transition temperature Tc of 18.6 K being achieved in RbB5 and the peak Vickers hardness Hv of 35.1 GPa being achieved in KB5 at 1 atm. The combination of these properties is particularly evident in KB5, RbB5, and BaB5, with Tc values of ∼14.7, 18.6, and 16.3 K and Hv values of ∼35.1, 32.4, and 33.8 GPa, respectively. The results presented here reveal that pentaborides can provide a framework for exploring and designing novel superconducting materials with favorable hardness at achievable pressures and even under ambient conditions. On the basis of the current theoretical understanding of boron-based hard superconductors under ambient conditions, numerous studies have been conducted with the aim of developing superconducting materials with favorable mechanical properties using boron-rich compounds. In this paper, first-principles calculations reveal the existence of an unprecedented family of tetragonal pentaborides MB5 (M = Na, K, Rb, Ca, Sr, Ba, Sc, and Y), comprising B20 cages and centered metal atoms acting as stabilizers and electron donors to the boron sublattice. These compounds exhibit both superconductivity and high hardness, with the maximum superconducting transition temperature Tc of 18.6 K being achieved in RbB5 and the peak Vickers hardness Hv of 35.1 GPa being achieved in KB5 at 1 atm. The combination of these properties is particularly evident in KB5, RbB5, and BaB5, with Tc values of ∼14.7, 18.6, and 16.3 K and Hv values of ∼35.1, 32.4, and 33.8 GPa, respectively. The results presented here reveal that pentaborides can provide a framework for exploring and designing novel superconducting materials with favorable hardness at achievable pressures and even under ambient conditions.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2023
- Vol. 8, Issue 5, 058404 (2023)
Discovery of the Baijifeng impact structure in Tonghua, Jilin, China
Ming Chen, Yang Lu, Jiahao Ning, Wenge Yang, Jinfu Shu, and Ho-kwang Mao
An impact structure 1400 m in diameter, formed by a bolide impact, has been discovered on Baijifeng Mountain in Tonghua City in Northeast China’s Jilin province. The impact structure takes the form of a cirque-shaped depression on the top of the mountain and is located in a basement mainly composed of Proterozoic sandstone and Jurassic granite. A large number of rock fragments composed mainly of sandstone, with a small amount of granite, are distributed on the top of Baijifeng Mountain. Planar deformation features (PDFs) have been found in quartz in the rock and mineral clasts collected from the surface inside the depression. The forms of the PDFs indexed in the quartz include among others, {101̄3}, {101̄2}, and {101̄1}. The presence of these PDFs provides diagnostic evidence for shock metamorphism and the impact origin of the structure. The impact event took place after the Jurassic Period and probably much later. An impact structure 1400 m in diameter, formed by a bolide impact, has been discovered on Baijifeng Mountain in Tonghua City in Northeast China’s Jilin province. The impact structure takes the form of a cirque-shaped depression on the top of the mountain and is located in a basement mainly composed of Proterozoic sandstone and Jurassic granite. A large number of rock fragments composed mainly of sandstone, with a small amount of granite, are distributed on the top of Baijifeng Mountain. Planar deformation features (PDFs) have been found in quartz in the rock and mineral clasts collected from the surface inside the depression. The forms of the PDFs indexed in the quartz include among others, {101̄3}, {101̄2}, and {101̄1}. The presence of these PDFs provides diagnostic evidence for shock metamorphism and the impact origin of the structure. The impact event took place after the Jurassic Period and probably much later.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2023
- Vol. 8, Issue 5, 058403 (2023)
Triggering dynamics of acetylene topochemical polymerization
Xingyu Tang, Xiao Dong, Chunfang Zhang, Kuo Li, Haiyan Zheng, and Ho-kwang Mao
Topochemical reactions are a promising method to obtain crystalline polymeric materials with distance-determined regio- or stereoselectivity. It has been concluded on an empirical basis that the closest intermolecular C⋯C distance in crystals of alkynes, d(C⋯C)min, should reach a threshold of ∼3 Å for bonding to occur at room temperature. To understand this empirical threshold, we study here the polymerization of acetylene in the crystalline state under high pressure by calculating the structural geometry, vibrational modes, and reaction profile. We find d(C⋯C)min to be the sum of an intrinsic threshold of 2.3 Å and a thermal displacement of 0.8 Å (at room temperature). Molecules at the empirical threshold move via several phonon modes to reach the intrinsic threshold, at which the intermolecular electronic interaction is sharply enhanced and bonding commences. A distance–vibration-based reaction picture is thus demonstrated, which provides a basis for the prediction and design of topochemical reactions, as well as an enhanced understanding of the bonding process in solids. Topochemical reactions are a promising method to obtain crystalline polymeric materials with distance-determined regio- or stereoselectivity. It has been concluded on an empirical basis that the closest intermolecular C⋯C distance in crystals of alkynes, d(C⋯C)min, should reach a threshold of ∼3 Å for bonding to occur at room temperature. To understand this empirical threshold, we study here the polymerization of acetylene in the crystalline state under high pressure by calculating the structural geometry, vibrational modes, and reaction profile. We find d(C⋯C)min to be the sum of an intrinsic threshold of 2.3 Å and a thermal displacement of 0.8 Å (at room temperature). Molecules at the empirical threshold move via several phonon modes to reach the intrinsic threshold, at which the intermolecular electronic interaction is sharply enhanced and bonding commences. A distance–vibration-based reaction picture is thus demonstrated, which provides a basis for the prediction and design of topochemical reactions, as well as an enhanced understanding of the bonding process in solids.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2023
- Vol. 8, Issue 5, 058402 (2023)
The near-room-temperature upsurge of electrical resistivity in Lu-H-N is not superconductivity, but a metal-to-poor-conductor transition
Di Peng, Qiaoshi Zeng, Fujun Lan, Zhenfang Xing, Yang Ding, and Ho-kwang Mao
The recent report of superconductivity in nitrogen-doped lutetium hydride (Lu-H-N) at 294 K and 1 GPa brought hope for long-sought-after ambient-condition superconductors. However, the failure of scientists worldwide to independently reproduce these results has cast intense skepticism on this exciting claim. In this work, using a reliable experimental protocol, we synthesized Lu-H-N while minimizing extrinsic influences and reproduced the sudden change in resistance near room temperature. With quantitative comparison of the temperature-dependent resistance between Lu-H-N and the pure lutetium before reaction, we were able to clarify that the drastic resistance change is most likely caused by a metal-to-poor-conductor transition rather than by superconductivity. Herein, we also briefly discuss other issues recently raised in relation to the Lu-H-N system. The recent report of superconductivity in nitrogen-doped lutetium hydride (Lu-H-N) at 294 K and 1 GPa brought hope for long-sought-after ambient-condition superconductors. However, the failure of scientists worldwide to independently reproduce these results has cast intense skepticism on this exciting claim. In this work, using a reliable experimental protocol, we synthesized Lu-H-N while minimizing extrinsic influences and reproduced the sudden change in resistance near room temperature. With quantitative comparison of the temperature-dependent resistance between Lu-H-N and the pure lutetium before reaction, we were able to clarify that the drastic resistance change is most likely caused by a metal-to-poor-conductor transition rather than by superconductivity. Herein, we also briefly discuss other issues recently raised in relation to the Lu-H-N system.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2023
- Vol. 8, Issue 5, 058401 (2023)
Partnership for eXtreme Xtallography (PX2)—A state-of-the-art experimental facility for extreme-conditions crystallography: A case study of pressure-induced phase transition in natural ilvaite
Jingui Xu, Dongzhou Zhang, Sergey N. Tkachev, and Przemyslaw K. Dera
Single-crystal x-ray diffraction (SCXRD) is an important tool to study the crystal structure and phase transitions of crystalline materials at elevated pressures. The Partnership for eXtreme Xtallography (PX2) program at the GSECARS 13-BM-C beamline of the Advanced Photon Source aims to provide state-of-the-art experimental capabilities to determine the crystal structures of materials under extreme conditions using SCXRD. PX2 provides a focused x-ray beam (12 × 18 µm2) at a monochromatic energy of 28.6 keV. High-pressure SCXRD experiments are performed with a six-circle diffractometer and a Pilatus3 photon-counting detector, facilitated by a membrane system for remote pressure control and an online ruby fluorescence system for pressure determination. The efficient, high-quality crystal structure determination at PX2 is exemplified by a study of pressure-induced phase transitions in natural ilvaite [CaFe2+2Fe3+Si2O7O(OH), P21/a space group]. Two phase transitions are observed at high pressure. The SCXRD data confirm the already-known ilvaite-I (P21/a) → ilvaite-II (Pnam) transformation at 0.4(1) GPa, and, a further phase transition is found to occur at 22.8(2) GPa where ilvaite-II transforms into ilvaite-III (P21/a). The crystal structure of the ilvaite-III is solved and refined in the P21/a space group. In addition to the ilvaite-I → ilvaite-II → ilvaite-III phase transitions, two minor structural modifications are observed as discontinuities in the evolution of the FeO6 polyhedral geometries with pressure, which are likely associated with magnetic transitions. Single-crystal x-ray diffraction (SCXRD) is an important tool to study the crystal structure and phase transitions of crystalline materials at elevated pressures. The Partnership for eXtreme Xtallography (PX2) program at the GSECARS 13-BM-C beamline of the Advanced Photon Source aims to provide state-of-the-art experimental capabilities to determine the crystal structures of materials under extreme conditions using SCXRD. PX2 provides a focused x-ray beam (12 × 18 µm2) at a monochromatic energy of 28.6 keV. High-pressure SCXRD experiments are performed with a six-circle diffractometer and a Pilatus3 photon-counting detector, facilitated by a membrane system for remote pressure control and an online ruby fluorescence system for pressure determination. The efficient, high-quality crystal structure determination at PX2 is exemplified by a study of pressure-induced phase transitions in natural ilvaite [CaFe2+2Fe3+Si2O7O(OH), P21/a space group]. Two phase transitions are observed at high pressure. The SCXRD data confirm the already-known ilvaite-I (P21/a) → ilvaite-II (Pnam) transformation at 0.4(1) GPa, and, a further phase transition is found to occur at 22.8(2) GPa where ilvaite-II transforms into ilvaite-III (P21/a). The crystal structure of the ilvaite-III is solved and refined in the P21/a space group. In addition to the ilvaite-I → ilvaite-II → ilvaite-III phase transitions, two minor structural modifications are observed as discontinuities in the evolution of the FeO6 polyhedral geometries with pressure, which are likely associated with magnetic transitions.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2022
- Vol. 7, Issue 2, 028401 (2022)
Static and dynamic diamond anvil cell (s-dDAC): A bidirectional remote controlled device for static and dynamic compression/decompression
Lei Su, Kaiyuan Shi, Li Zhang, Yanlong Wang, and Guoqiang Yang
A novel bidirectional remotely controlled device for static and dynamic compression/decompression using diamond anvil cells (DACs) has been developed that can control pressure in an accurate and consistent manner. Electromechanical piezoelectric actuators are applied to a conventional DAC, allowing applications under a variety of pressure conditions. Using this static and dynamic DAC (s-dDAC), it is possible to addresses the poorly studied experimental regime lying between purely static and purely dynamic studies. The s-dDAC, driven by three piezoelectric actuators, can be combined with a time-resolved spectral measurement system and high-speed imaging device to study the structural changes, chemical reactions, and properties of materials under extreme conditions. The maximum compression/decompression rate or pressure range highly depends on the culet size of the anvil, and a higher compression rate and wider pressure range can be realized in a DAC with smaller anvil culet. With our s-dDAC, we have been able to achieve the highest compression rate to date with a 300 μm culet anvil: 48 TPa/s. An overview of a variety of experimental measurements possible with our device is presented. A novel bidirectional remotely controlled device for static and dynamic compression/decompression using diamond anvil cells (DACs) has been developed that can control pressure in an accurate and consistent manner. Electromechanical piezoelectric actuators are applied to a conventional DAC, allowing applications under a variety of pressure conditions. Using this static and dynamic DAC (s-dDAC), it is possible to addresses the poorly studied experimental regime lying between purely static and purely dynamic studies. The s-dDAC, driven by three piezoelectric actuators, can be combined with a time-resolved spectral measurement system and high-speed imaging device to study the structural changes, chemical reactions, and properties of materials under extreme conditions. The maximum compression/decompression rate or pressure range highly depends on the culet size of the anvil, and a higher compression rate and wider pressure range can be realized in a DAC with smaller anvil culet. With our s-dDAC, we have been able to achieve the highest compression rate to date with a 300 μm culet anvil: 48 TPa/s. An overview of a variety of experimental measurements possible with our device is presented.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2022
- Vol. 7, Issue 1, 018401 (2022)
Theoretical models of void nucleation and growth for ductile metals under dynamic loading: A review
Haonan Sui, Long Yu, Wenbin Liu, Ying Liu, Yangyang Cheng, and Huiling Duan
Void nucleation and growth under dynamic loading are essential for damage initiation and evolution in ductile metals. In the past few decades, the development of experimental techniques and simulation methods has helped to reveal a wealth of information about the nucleation and growth process from its microscopic aspects to macroscopic ones. Powerful and effective theoretical approaches have been developed based on this information and have helped in the analysis of the damage states of structures, thereby making an important contribution to the design of damage-resistant materials. This Review presents a brief overview of theoretical models related to the mechanisms of void nucleation and growth under dynamic loading. Classical work and recent research progress are summarized, together with discussion of some aspects deserving further study. Void nucleation and growth under dynamic loading are essential for damage initiation and evolution in ductile metals. In the past few decades, the development of experimental techniques and simulation methods has helped to reveal a wealth of information about the nucleation and growth process from its microscopic aspects to macroscopic ones. Powerful and effective theoretical approaches have been developed based on this information and have helped in the analysis of the damage states of structures, thereby making an important contribution to the design of damage-resistant materials. This Review presents a brief overview of theoretical models related to the mechanisms of void nucleation and growth under dynamic loading. Classical work and recent research progress are summarized, together with discussion of some aspects deserving further study.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2022
- Vol. 7, Issue 1, 018201 (2022)
Born’s valence force-field model for diamond at terapascals: Validity and implications for the primary pressure scale
Qingyang Hu, and Ho-kwang Mao
Born’s valence force-field model (VFM) established a theoretical scheme for calculating the elasticity, zero-point optical mode, and lattice dynamics of diamond and diamond-structured solids. In particular, the model enabled the derivation of a numerical relation between the elastic moduli and the Raman-active F2g mode for diamond. Here, we establish a relation between the diamond Raman frequency ω and the bulk modulus K through first-principles calculation, rather than extrapolation. The calculated K exhibits a combined uncertainty of less than 5.4% compared with the results obtained from the analytical equation of the VFM. The results not only validate Born’s classic model but also provide a robust K–ω functional relation extending to megabar pressures, which we use to construct a primary pressure scale through Raman spectroscopy and the crystal structure of diamond. Our computations also suggest that currently used pressure gauges may seriously overestimate pressures in the multi-megabar regime. A revised primary scale is urgently needed for such ultrahigh pressure experiments, with possible implications for hot superconductors, ultra-dense hydrogen, and the structure of the Earth’s core. Born’s valence force-field model (VFM) established a theoretical scheme for calculating the elasticity, zero-point optical mode, and lattice dynamics of diamond and diamond-structured solids. In particular, the model enabled the derivation of a numerical relation between the elastic moduli and the Raman-active F2g mode for diamond. Here, we establish a relation between the diamond Raman frequency ω and the bulk modulus K through first-principles calculation, rather than extrapolation. The calculated K exhibits a combined uncertainty of less than 5.4% compared with the results obtained from the analytical equation of the VFM. The results not only validate Born’s classic model but also provide a robust K–ω functional relation extending to megabar pressures, which we use to construct a primary pressure scale through Raman spectroscopy and the crystal structure of diamond. Our computations also suggest that currently used pressure gauges may seriously overestimate pressures in the multi-megabar regime. A revised primary scale is urgently needed for such ultrahigh pressure experiments, with possible implications for hot superconductors, ultra-dense hydrogen, and the structure of the Earth’s core.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2021
- Vol. 6, Issue 6, 068403 (2021)
In situ high-pressure nuclear magnetic resonance crystallography in one and two dimensions
Thomas Meier, Alena Aslandukova, Florian Trybel, Dominique Laniel, Takayuki Ishii, Saiana Khandarkhaeva, Natalia Dubrovinskaia, and Leonid Dubrovinsky
Recent developments in in situ nuclear magnetic resonance (NMR) spectroscopy under extreme conditions have led to the observation of a wide variety of physical phenomena that are not accessible with standard high-pressure experimental probes. However, inherent di- or quadrupolar line broadening in diamond anvil cell (DAC)-based NMR experiments often limits detailed investigation of local atomic structures, especially if different phases or local environments coexist. Here, we describe our progress in the development of high-resolution NMR experiments in DACs using one- and two-dimensional homonuclear decoupling experiments at pressures up to the megabar regime. Using this technique, spectral resolutions of the order of 1 ppm and below have been achieved, enabling high-pressure structural analysis. Several examples are presented that demonstrate the wide applicability of this method for extreme conditions research. Recent developments in in situ nuclear magnetic resonance (NMR) spectroscopy under extreme conditions have led to the observation of a wide variety of physical phenomena that are not accessible with standard high-pressure experimental probes. However, inherent di- or quadrupolar line broadening in diamond anvil cell (DAC)-based NMR experiments often limits detailed investigation of local atomic structures, especially if different phases or local environments coexist. Here, we describe our progress in the development of high-resolution NMR experiments in DACs using one- and two-dimensional homonuclear decoupling experiments at pressures up to the megabar regime. Using this technique, spectral resolutions of the order of 1 ppm and below have been achieved, enabling high-pressure structural analysis. Several examples are presented that demonstrate the wide applicability of this method for extreme conditions research.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2021
- Vol. 6, Issue 6, 068402 (2021)
Effect of the projector augmented wave potentials on the simulation of thermodynamic properties of vanadium
Tingting Zhang, Yuechao Wang, Jiawei Xian, Shuaichuang Wang, Jun Fang, Suqing Duan, Xingyu Gao, Haifeng Song, and Haifeng Liu
We report significant differences in high-pressure properties of vanadium at zero temperature and finite temperature when different projector augmented wave (PAW) potentials are used in simulations based on density functional theory. When a PAW potential with only five electrons taken as valence electrons is used, the cold pressures in the high-pressure region are seriously underestimated, and an abnormality occurs in the melting curve of vanadium at about 400 GPa. We show that the reason for these discrepancies lies in the differences in the descriptions of the interatomic force, electron dispersion, and anisotropy of electron bonding obtained from different PAW potentials at high pressure, which lead to striking differences in the mechanical stability of the system. We propose a procedure for selecting PAW potentials suitable for simulations at high temperature and high pressure. Our results provide valuable guidance for future simulations of thermodynamic properties under extreme conditions. We report significant differences in high-pressure properties of vanadium at zero temperature and finite temperature when different projector augmented wave (PAW) potentials are used in simulations based on density functional theory. When a PAW potential with only five electrons taken as valence electrons is used, the cold pressures in the high-pressure region are seriously underestimated, and an abnormality occurs in the melting curve of vanadium at about 400 GPa. We show that the reason for these discrepancies lies in the differences in the descriptions of the interatomic force, electron dispersion, and anisotropy of electron bonding obtained from different PAW potentials at high pressure, which lead to striking differences in the mechanical stability of the system. We propose a procedure for selecting PAW potentials suitable for simulations at high temperature and high pressure. Our results provide valuable guidance for future simulations of thermodynamic properties under extreme conditions.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2021
- Vol. 6, Issue 6, 068401 (2021)
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