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2. Stability of xenon-sodium compounds at moderately low pressures

Author

Wang, Shaoxiong, Dong, Huafeng, Peng, Junhao, Wen, Minru, Zhang, Xin, Wu, Fugen, Goncharov, Alexander F., and Oganov, Artem R.

Subjects
Condensed Matter - Materials Science
Abstract

A growing body of theoretical and experimental evidence suggests that inert gases (He, Ne, Ar, Kr, Xe, Rn) become less and less inert under increasing pressure. Here we use the ab initio evolutionary algorithm to predict stable compounds of Xe and Na at pressures below 100 GPa, and find three stable compounds, NaXe, NaXe$_3$ and NaXe$_4$. The NaXe belongs to a well-known cubic CsCl structure type. The NaXe$_4$'s structure is common in amphiboles, whereas the NaXe$_3$ has a unique structure, analogous to the "post-perovskite" orthorhombic CaIrO$_3$-type structure with Ir atoms removed. This is the first time that a cation-vacant version of the CaIrO$_3$ is found in any compound. NaXe, NaXe$_3$ and NaXe$_4$ are found to be metallic.

Published
2022

42. Effect of surface polarization and structural deformation on the formation and stabilization of polarons in two-dimensional Ruddlesden–Popper metal halide perovskites.

Author

Liu, Yongsi, Liao, Haijun, Huang, Le, Xiao, Ye, Wen, Minru, Dong, Huafeng, Wu, Fugen, and Feng, Xing

Subjects
METAL halides, PEROVSKITE, DEFORMATION of surfaces, POLARONS, DIPOLE moments, DEFORMATIONS (Mechanics), ELECTRON distribution
Abstract

First-principles density-functional theory calculations were performed to reveal the effect of surface polarization and structural deformation on the formation and stabilization of the polaron in two-dimensional Ruddlesden–Popper perovskites. Our results revealed that the orientational distribution of organic cations induces surface polarization. The surface dipole moment can be well featured by the c axis distances between N and the nearest I atoms. Structural deformation and surface dipole moments result in separate real-space distributions of hole and electron polarons. Our results also reveal that the structural deformation of the [PbI6] sublattices and surface polarization are closely related to the reorientation of organic cations and can be effectively modulated by it. This reorientation significantly impacts the stabilization of polarons. Our understandings provide insight into the nature of polarons in two-dimensional Ruddlesden–Popper perovskites and general guidance for the proper selection of organic cations in two-dimensional perovskites for suitable applications in photovoltaic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Published
2023
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46. Super Broadband Emission Across NIR‐I and NIR‐II Under Blue Light Excitation of Cr3+, Ni2+ Co‐Doped Sr2GaTaO6 Phosphor Achieved by Two‐Site Occupation and Effective Energy Transfer.

Author

Zhuo, Yifu, Wu, Fugen, Niu, Yaping, Wang, Yun, zhang, Qi, Teng, Yun, Dong, Huafeng, and Mu, Zhongfei

Subjects
*NIGHT vision, *ENERGY transfer, *PHOSPHORS, *ORGANIC compounds, *DIODES
Abstract

The performance of the near‐infrared phosphor‐converted light‐emitting diodes (NIR pc‐LEDs) mainly depends on the NIR emitting phosphors used. Cr3+ doped materials can be excited by blue light chips, but their emission is located in the NIR‐I region (650–1000 nm). Ni2+ doped materials are mainly located in the NIR‐II region (1000–1700 nm), but they cannot be effectively excited by blue light chips. Herein, Cr3+, Ni2+ mono‐doped, and co‐doped Sr2GaTaO6 NIR emitting phosphors are prepared and investigated. Cr3+ and Ni2+ ions occupy two octahedral sites of Ga3+ and Ta5+. The co‐doping of Cr3+ ions has achieved two breakthroughs. One is to shift the optimal excitation wavelength from violet light to blue light due to the energy transfer (efficiency up to 70%) from Cr3+ to Ni2+. The other is to achieve the broadband and continuous emission across NIR‐I and NIR‐II regions (650–1700 nm, with a full width at half maximum (FWHM) of 410 nm (173 nm + 237 nm)). The prepared Sr2GaTaO6: 0.02Cr3+, 0.01Ni2+ phosphor is combined with a commercial 460 nm blue chip to realize its application in organic compounds identification, night vision, and biological imaging. This work points out a direction for the future development of efficient super broadband NIR‐emitting phosphors. [ABSTRACT FROM AUTHOR]

Published
2024
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49. Prediction of a new ground state of superhard compound B6O at ambient conditions

Author

Dong, Huafeng, Oganov, Artem R., Wang, Qinggao, Wang, Sheng-Nan, Wang, Zhenhai, Zhang, Jin, Esfahani, M. Mahdi Davari, Zhou, Xiang-Feng, Wu, Fugen, and Zhu, Qiang

Subjects
Condensed Matter - Materials Science
Abstract

Boron suboxide B6O, the hardest known oxide, has an R-3m crystal structure ({\alpha}-B6O) that can be described as an oxygen-intercalated structure of {\alpha}-boron, or, equivalently, as a cubic close packing of B12 icosahedra with two oxygen atoms occupying all octahedral voids in it. Here we show a new ground state of this compound at ambient conditions, Cmcm-B6O (\b{eta}-B6O), which in all quantum-mechanical treatments that we tested (GGA, LDA, and hybrid functional HSE06) comes out to be slightly but consistently more stable. Increasing pressure and temperature further stabilize it with respect to the known {\alpha}-B6O structure. \b{eta}-B6O also has a slightly higher hardness and may be synthesized using different experimental protocols. We suggest that \b{eta}-B6O is present in mixture with {\alpha}-B6O, and its presence accounts for previously unexplained bands in the experimental Raman spectrum., Comment: 12 pages

Published
2016

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