| 1. |
- Ji, Cheng, et al.
(författare)
-
Crystallography of low Z material at ultrahigh pressure : Case study on solid hydrogen
- 2020
-
Ingår i: Matter and Radiation at Extremes. - : American Institute of Physics (AIP). - 2468-2047 .- 2468-080X. ; 5:3
-
Tidskriftsartikel (refereegranskat)abstract
- Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensed matter. However, the only way to determine crystal structures of materials above 100 GPa, namely, X-ray diffraction (XRD), especially for low Z materials, remains nontrivial in the ultrahigh-pressure region, even with the availability of brilliant synchrotron X-ray sources. In this work, we perform a systematic study, choosing hydrogen (the lowest X-ray scatterer) as the subject, to understand how to better perform XRD measurements of low Z materials at multimegabar pressures. The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254 GPa at room temperature [C. Ji et al., Nature 573, 558–562 (2019)]. We present our discoveries and experiences with regard to several aspects of this work, namely, diamond anvil selection, sample configuration for ultrahigh-pressure XRD studies, XRD diagnostics for low Z materials, and related issues in data interpretation and pressure calibration. We believe that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures, eventually testing structural models of metallic hydrogen.
|
|
| 2. |
- Ji, Cheng, et al.
(författare)
-
Ultrahigh-pressure isostructural electronic transitions in hydrogen
- 2019
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 573:7775, s. 558-562
-
Tidskriftsartikel (refereegranskat)abstract
- High-pressure transitions are thought to modify hydrogen molecules to a molecular metallic solid and finally to an atomic metal(1), which is predicted to have exotic physical properties and the topology of a two-component (electron and proton) superconducting superfluid condensate(2,3). Therefore, understanding such transitions remains an important objective in condensed matter physics(4,5). However, measurements of the crystal structure of solid hydrogen, which provides crucial information about the metallization of hydrogen under compression, are lacking for most high-pressure phases, owing to the considerable technical challenges involved in X-ray and neutron diffraction measurements under extreme conditions. Here we present a single-crystal X-ray diffraction study of solid hydrogen at pressures of up to 254 gigapascals that reveals the crystallographic nature of the transitions from phase I to phases III and IV. Under compression, hydrogen molecules remain in the hexagonal close-packed (hcp) crystal lattice structure, accompanied by a monotonic increase in anisotropy. In addition, the pressure-dependent decrease of the unit cell volume exhibits a slope change when entering phase IV, suggesting a second-order isostructural phase transition. Our results indicate that the precursor to the exotic two-component atomic hydrogen may consist of electronic transitions caused by a highly distorted hcp Brillouin zone and molecular-symmetry breaking.
|
|
| 3. |
- Liu, Lei, 1982-
(författare)
-
Synthesis and Tuning of Multifunctional Materials at High Pressure
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- At the present stage, human society is developing at an unprecedented speed, facing an emergence of highly pressing challenges, e.g., information explosion, energy production problems, environmental pollution, climate problems. Functional materials with tailored properties are considered as holding a key to solving these problems. In this thesis, high-pressure techniques were employed to synthesize and tune the properties of multiferroic materials relevant to spintronic and light-harvesting applications, and multifunctional high-entropy alloys.Melanostibite (Mn2FeSbO6, MFSO) is a very rare mineral discovered in Sweden. Previous studies indicate it is a potential multiferroic material with foreseen applications in information storage and spintronic devices. However, its multiferroic phase has not been synthesized yet. Herein, the structural evolution of MFSO was studied up to ~50 GPa, and the LiNbO3-type MFSO was synthesized at high pressure and moderate temperature. As a polar structure material, the LiNbO3-type MFSO represents a promising candidate for multiferroic materials. The double perovskite, Pb2CoTeO6, was also compressed to ~60 GPa, while no polar phase was discovered. The obtained results provide guidance to the synthesis of new multiferroic double perovskite.Solar energy is a promising alternative to fossil fuels and thus a viable solution to the global energy problem. Light-harvesting materials, which absorb sunlight and transform it into electricity by the photovoltaic effect, represent the core part of solar cells. Currently, the dominant commercial light-harvesting material is silicon. However, silicon and recently emerged organic-inorganic perovskites have several drawbacks. Multiferroic oxides are considered as stable and nontoxic light-harvesting materials. But, their bandgap energies are generally too large for photovoltaic applications. Herein, high-pressure technique was applied to treat Mn3TeO6, and a quenchable phase of Mn3TeO6 displaying a greatly narrowed bandgap was synthesized. The measured absorption spectrum of the quenched phase reveals that it may be suitable for photovoltaic applications. The present research opens a green way to tune the bandgap energy of multiferroic.High-entropy alloys (HEAs) were first synthesized in 2004. However, knowledge of this new class of promising alloys is still very limited, even in very fundamental aspects. The present results reveal that lattice distortion plays important roles in the phase transition of HEAs, and demonstrate the future possibility of designing the Invar high-entropy alloy, a promising structural material. The results show that it is possible to combine several practical properties in a single alloy, which will widen the range of applications of HEAs. The presented research demonstrates that high-pressure represents an effective way to tune various properties of materials, as well as can be applied for the synthesis of materials with exotic properties which are usually not stable or attainable at ambient conditions.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Shen, Guoyin, et al.
(författare)
-
Effect of helium on structure and compression behavior of SiO2 glass
- 2011
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:15, s. 6004-6007
-
Tidskriftsartikel (refereegranskat)abstract
- The behavior of volatiles is crucial for understanding the evolution of the Earth's interior, hydrosphere, and atmosphere. Noble gases as neutral species can serve as probes and be used for examining gas solubility in silicate melts and structural responses to any gas inclusion. Here, we report experimental results that reveal a strong effect of helium on the intermediate range structural order of SiO2 glass and an unusually rigid behavior of the glass. The structure factor data show that the first sharp diffraction peak position of SiO2 glass in helium medium remains essentially the same under pressures up to 18.6 GPa, suggesting that helium may have entered in the voids in SiO2 glass under pressure. The dissolved helium makes the SiO2 glass much less compressible at high pressures. GeO2 glass and SiO2 glass with H-2 as pressure medium do not display this effect. These observations suggest that the effect of helium on the structure and compression of SiO2 glass is unique.
|
|
| 7. |
|
|
| 8. |
|
|
