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51. Concurrent Pressure-Induced Spin-State Transitions and Jahn–Teller Distortions in MnTe

Author

Wang, Pei, primary, Zhu, Sheng-Cai, additional, Zou, Yongtao, additional, Chen, Haiyan, additional, Liu, Ying, additional, Li, Weiwei, additional, Chen, Jian, additional, Zhu, Jinlong, additional, Wu, Liusuo, additional, Wang, Shanmin, additional, Yang, Wenge, additional, Xiao, Yuming, additional, Chow, Paul, additional, Wang, Liping, additional, and Zhao, Yusheng, additional

Published
2022
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54. The Future of FPGA Acceleration in Datacenters and the Cloud

Author

Bobda, Christophe, primary, Mbongue, Joel Mandebi, additional, Chow, Paul, additional, Ewais, Mohammad, additional, Tarafdar, Naif, additional, Vega, Juan Camilo, additional, Eguro, Ken, additional, Koch, Dirk, additional, Handagala, Suranga, additional, Leeser, Miriam, additional, Herbordt, Martin, additional, Shahzad, Hafsah, additional, Hofste, Peter, additional, Ringlein, Burkhard, additional, Szefer, Jakub, additional, Sanaullah, Ahmed, additional, and Tessier, Russell, additional

Published
2022
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63. Resonant X-ray emission study of the lower-mantle ferropericlase at high pressures

Author

Lin, Jung-Fu, Mao, Zhu, Jarrige, Ignace, Xiao, Yuming, Chow, Paul, Okuchi, Takuo, Hiraoka, Nozomu, and Jacobsen, Steven O.

Subjects
Materials at high pressures -- Evaluation, Magnesium compounds -- Properties, X-ray spectroscopy -- Methods, Earth sciences
Abstract

Electronic states of iron in Earth's mantle minerals including ferropericlase, silicate perovskite, and post-perovskite have been previously investigated at high pressures and/or temperatures using various experimental techniques, including X-ray emission and Mossbauer spectroscopies. Although such methods have been used to infer changes in the electronic spin and valence states of iron in lower mantle minerals, they do not directly probe the 3d electronic states quantitatively. Here we use 1s2p resonant X-ray emission spectroscopy (RXES) at the Fe K pre-edge to directly probe and assess the 3d electronic states and the crystal-field splittings of [Fe.sup.2+] in the lower-mantle ferropericlase [([Mg.sub.0.75],[Fe.sub.0.25]) O] at pressures up to 90 GPa. The pre-edge features from X-ray absorption spectroscopy in the partial fluorescence yield (PFY-XAS) and RXES results explicitly show three excited states for high-spin [Fe.sup.2+] (a lower-energy [sup.4][T.sub.1g] state, a [sup.4][T.sub.2g] state, and a higher-energy [sup.4][T.sub.1g] state) and a single [sup.2][E.sub.g] state for low-spin [Fe.sub.2+], attributed to the [([t.sub.2g]).sup.0][([e.sub.g]).sup.3] excited configuration. This latter feature begins to appear at 48 GPa and grows with pressure, while the peaks related to high-spin [Fe.sup.2+] vanish above 80 GPa. The observed pre-edge features are consistent with purely quadrupolar transitions resulting from the centrosymmetric character of the [Fe.sup.2+] site. The K pre-edge RXES spectra at the incident energy of 7112 eV, which are similar to the Fe L-edge spectra, are also used successfully to quantitatively obtain consistent results on the spin transition of [Fe.sup.2+] in ferropericlase under high pressures. Owing to the superior sensitivity of the RXES technique, the observed electronic states and their energy separations provide direct information on the local electronic structures and crystal-field splitting energies of the 3d electronic shells of [Fe.sup.2+] in ferropericlase at relevant pressures of the Earth's lower mantle. Keywords: Ferropericlase, diamond anvil cell, spin transition, resonant X-ray emission spectroscopy, partial fluorescence yield, high pressures DOI: 10.2138/am.2010.3495

Published
2010

73. Probing the Electronic Band Gap of Solid Hydrogen by Inelastic X-Ray Scattering up to 90 GPa

Author

Li, Bing, primary, Ding, Yang, additional, Kim, Duck Young, additional, Wang, Lin, additional, Weng, Tsu-Chien, additional, Yang, Wenge, additional, Yu, Zhenhai, additional, Ji, Cheng, additional, Wang, Junyue, additional, Shu, Jinfu, additional, Chen, Jiuhua, additional, Yang, Ke, additional, Xiao, Yuming, additional, Chow, Paul, additional, Shen, Guoyin, additional, Mao, Wendy L., additional, and Mao, Ho-Kwang, additional

Published
2021
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74. Spin transition of iron in magnesiowustite in the Earth's lower mantle

Author

Lin, Jung-Fu, Struzhkin, Viktor V., Jacobsen, Steven D., Hu, Michael Y., Chow, Paul, Kung, Jennifer, Liu, Haozhe, Mao, Ho-kwang, and Hemley, Russell J.

Subjects
Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Author(s): Jung-Fu Lin (corresponding author) [1, 4]; Viktor V. Struzhkin [1]; Steven D. Jacobsen [1]; Michael Y. Hu [2]; Paul Chow [2]; Jennifer Kung [3]; Haozhe Liu [2]; Ho-kwang Mao [...]

Published
2005
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77. Pressure-Induced Collapse of Magnetic Order in Jarosite

Author

Klein, Ryan A., primary, Walsh, James P. S., additional, Clarke, Samantha M., additional, Liu, Zhenxian, additional, Alp, E. Ercan, additional, Bi, Wenli, additional, Meng, Yue, additional, Altman, Alison B., additional, Chow, Paul, additional, Xiao, Yuming, additional, Norman, M. R., additional, Rondinelli, James M., additional, Jacobsen, Steven D., additional, Puggioni, Danilo, additional, and Freedman, Danna E., additional

Published
2020
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82. Shape Dependence of Pressure-Induced Phase Transition in CdS Semiconductor Nanocrystals

Author

Meng, Lingyao, primary, Lane, J. Matthew D., additional, Baca, Luke, additional, Tafoya, Jackie, additional, Ao, Tommy, additional, Stoltzfus, Brian, additional, Knudson, Marcus, additional, Morgan, Dane, additional, Austin, Kevin, additional, Park, Changyong, additional, Chow, Paul, additional, Xiao, Yuming, additional, Li, Ruipeng, additional, Qin, Yang, additional, and Fan, Hongyou, additional

Published
2020
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83. Magnetic phase diagram of ɛ′ -FeH

Author

Ying, Jianjun, primary, Zhao, Jiyong, additional, Bi, Wenli, additional, Alp, E. Ercan, additional, Xiao, Yuming, additional, Chow, Paul, additional, Shen, Guoyin, additional, and Struzhkin, Viktor V., additional

Published
2020
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84. A scheduler ASIC for a programmable packet switch

Author

Zhang, L. Louis, Beacham, Brent, Hashemi, Massoud Reza, Chow, Paul, and Leon-Garcia, Alberto

Subjects
Application-specific integrated circuits -- Research, Computers -- Research, Packet switching -- Research
Published
2000

88. Pressure-Driven Changes in the Electronic Bonding Environment of GeO2Glass above Megabar Pressures

Author

Kim, Yong-Hyun, Yi, Yoo Soo, Kim, Hyo-Im, Chow, Paul, Xiao, Yuming, Shen, Guoyin, and Lee, Sung Keun

Abstract

Noncrystalline oxides under pressure undergo gradual structural modifications, highlighted by the formation of a dense noncrystalline network topology. The nature of the densified networks and their electronic structures at high pressures may account for the mechanical hardening and the anomalous changes in electromagnetic properties. Despite its importance, direct probing of the electronic structures in amorphous oxides under compression above the Mbar pressure (>100 GPa) is currently lacking. Here, we report the observation of pressure-driven changes in electronic configurations and their delocalization around oxygen in glasses using inelastic X-ray scattering spectroscopy (IXS). In particular, the first O K-edge IXS spectra for compressed GeO2glass up to 148 GPa, the highest pressure ever reached in an experimental study of GeO2glass, reveal that the glass densification results from a progressive increase of oxygen proximity. While the triply coordinated oxygen [3]O is dominant below ∼50 GPa, the IXS spectra resolve multiple edge features that are unique to topologically disordered [4]O upon densification above 55 GPa. Topological compaction in GeO2glass above 100 GPa results in pronounced electronic delocalization, revealing the contribution from Ge d-orbitals to oxide densification. Strong correlations between the glass density and the electronic configurations beyond the Mbar conditions highlight the electronic origins of densification of heavy-metal-bearing oxide glasses. Current experimental breakthroughs shed light on the direct probing of the electronic density of states in high-Zoxides above 1 Mbar, offering prospects for studies on the pressure-driven changes in magnetism, superconductivity, and electronic transport properties in heavy-metal-bearing oxides under compression.

Published
2022
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89. Structural and electronic phase transitions of Co2Te3O8 spiroffite under high pressure

Author

Li, Nana, Manoun, Bouchaib, Tamraoui, Youssef, Zhang, Qian, Dong, Haini, Xiao, Yuming, Chow, Paul, Lazor, Peter, Lu, Xujie, Wang, Yonggang, Yang, Wenge, Li, Nana, Manoun, Bouchaib, Tamraoui, Youssef, Zhang, Qian, Dong, Haini, Xiao, Yuming, Chow, Paul, Lazor, Peter, Lu, Xujie, Wang, Yonggang, and Yang, Wenge

Abstract

The structural and electronic phase transitions of Co2Te3O8 spiroffite have been studied with a suite of in situ high-pressure characterization techniques including synchrotron x-ray diffraction, Raman, x-ray emission spectroscopy, UV-vis absorption, and electrical transport measurement. Two pressure-induced phase transitions were observed at about 6.9 and 14.4 GPa. The first transition is attributed to a small spin transition of Co along with discontinuity in unit-cell volume change, while the second one represents a first-order phase transition with a volume collapse of 4.5%. The latter transition is accompanied by the relaxation of distortion in CoO6 octahedron, which enhances the crystal-field strength inhibiting the occurrence of spin transition. What is more, the competition between contributions of electrons and oxygen ion to the overall conductivity is observed and affected by the phase transition under high pressure. This demonstration provides insights into the relationship between the lattice-structural and spin degrees of freedom, and highlights the impact of pressure on the control of structural and electronic states of a given material for optimized functionalities.

Published
2019
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90. Pressure-enhanced interplay between lattice, spin, and charge in the mixed perovskite La2FeMnO6

Author

Li, Nana, Fan, Fengren, Sun, Fei, Wang, Yonggang, Zhao, Yongsheng, Liu, Fengliang, Zhang, Qian, Ikuta, Daijo, Xiao, Yuming, Chow, Paul, Heald, Steve M., Sun, Chengjun, Brewe, Dale, Li, Aiguo, Lu, Xujie, Mao, Ho-kwang, Khomskii, Daniel, I, Wu, Hua, Yang, Wenge, Li, Nana, Fan, Fengren, Sun, Fei, Wang, Yonggang, Zhao, Yongsheng, Liu, Fengliang, Zhang, Qian, Ikuta, Daijo, Xiao, Yuming, Chow, Paul, Heald, Steve M., Sun, Chengjun, Brewe, Dale, Li, Aiguo, Lu, Xujie, Mao, Ho-kwang, Khomskii, Daniel, I, Wu, Hua, and Yang, Wenge

Abstract

Spin crossover plays a central role in the structural instability, net magnetic moment modification, metallization, and even in superconductivity in corresponding materials. Most reports on the pressure-induced spin crossover with a large volume collapse have so far focused on compounds with a single transition metal. Here we report a comprehensive high-pressure investigation of a mixed Fe-Mn perovskite La2FeMnO6. Under pressure, the strong coupling between Fe andMn leads to a combined valence/spin transition: Fe3+(S = 5/2) -> Fe2+(S = 0) and Mn3+(S = 2) -> Mn4+(S = 3/2), with an isostructural phase transition. The spin transitions of both Fe and Mn are offset by similar to 20 GPa of the onset pressure, and the lattice collapse occurs in between. Interestingly, Fe3+ ion shows an abnormal behavior when it reaches a lower valence state (Fe2+) accompanied by a +0.5 eV energy shift in the Fe K-absorption edge at 15 GPa. This process is associated with the charge-spin-orbital state transition from high spin Fe3+ to low spin Fe2+, caused by the significantly enhanced t(2g)-e(g) crystal field splitting in the compressed lattice under high pressure. Density functional theory calculations confirm the energy preference of the high-pressure state with charge redistribution accompanied by spin state transition of Fe ions. Moreover, La2FeMnO6 maintains semiconductor behaviors even when the pressure reached 144.5 GPa as evidenced by the electrical transport measurements, despite the huge resistivity decreasing seven orders of magnitude compared with that at ambient pressure. The investigation carried out here demonstrates high flexibility of double perovskites and their good potentials for optimizing the functionality of these materials.

Published
2019

91. Spectroscopic evidence for the Fe3+ spin transition in iron-bearing δ-AlOOH at high pressure.

Author

XIAOWAN SU, CHAOSHUAI ZHAO, IANGXU XU, CHAOJIA LV, XITONG SONG, TAKAYUKI ISHII, YUMING XIAO, CHOW, PAUL, QIANG SUN, and JIN LIU

Subjects
SPIN crossover, X-ray emission spectroscopy, PLANETARY interiors, IRON
Abstract

δ-AlOOH has emerged as a promising candidate for water storage in the lower mantle and could have delivered water into the bottom of the mantle. To date, it still remains unclear how the presence of iron affects its elastic, rheological, vibrational, and transport properties, especially across the spin cross-over. Here, we conducted high-pressure X-ray emission spectroscopy experiments on a δ-(Al0.85Fe0.15) OOH sample up to 53 GPa using silicone oil as the pressure transmitting medium in a diamonδ-Anvil cell. We also carried out laser Raman measurements on δ-(Al0.85Fe0.15)OOH and δ-(Al0.52Fe0.48)OOH up to 57 and 62 GPa, respectively, using neon as the pressure-transmitting medium. Evolution of Raman spectra of δ-(Al[sub 0.85]Fe[sub 0.15])OOH with pressure shows two new bands at 226 and 632 cm-1 at 6.0 GPa, in agreement with the transition from an ordered (P21nm) to a disordered hydrogen bonding structure (Pnnm) for δ-AlOOH. Similarly, the two new Raman bands at 155 and 539 cm-1 appear in δ-(Al0.52 Fe0.48)OOH between 8.5 and 15.8 GPa, indicating that the incorporation of 48 mol% FeOOH could postpone the order-disorder transition upon compression. On the other hand, the satellite peak (Kβ') intensity of δ-(Al0.85Fe0.15)OOH starts to decrease at ~30 GPa and it disappears completely at 42 GPa. That is, δ-(Al0.85 Fe0.15)OOH undergoes a gradual electronic spin-pairing transition at 30-42 GPa. Furthermore, the pressure dependence of Raman shifts of δ-(Al0.85Fe0.15)OOH discontinuously decreases at 32-37 GPa, suggesting that the improved hydrostaticity by the use of neon pressure medium could lead to a relatively narrow spin crossover. Notably, the pressure dependence of Raman shifts and optical color of δ-(Al0.52Fe0.48)OOH dramatically change at 41-45 GPa, suggesting that it probably undergoes a relatively sharp spin transition in the neon pressure medium. Together with literature data on the solid solutions between δ-AlOOH and ε-FeOOH, we found that the onset pressure of the spin transition in δ-(Al,Fe)OOH increases with increasing FeOOH content. These results shed new insights into the effects of iron on the structural evolution and vibrational properties of δ-AlOOH. The presence of FeOOH in δ-AlOOH can substantially influence its high-pressure behavior and stability at the deep mantle conditions and play an important role in the deep-water cycle. [ABSTRACT FROM AUTHOR]

Published
2021
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93. A multiprocessor architecture for viterbi decoders with linear speedup

Author

Feygin, Gennady, Gulak, Patrick G., and Chow, Paul

Subjects
Multiprocessors -- Design and construction, Decoders -- Research, Linear systems -- Research, Algorithms -- Research, Business, Computers, Electronics, Electronics and electrical industries
Abstract

The generalized cascade Viterbi decoder (GCVD) architectures are implemented as ring structures with unidirectional local communication for a binary alphabet. This family of architectures is suitable for the implementation of VLSI. The GCVD architecture efficiently uses from the nu minus 1 processors in deciphering a single group of data. For GCVD all the processes are used in the various stages of data analysis.

Published
1993

94. Electronic transitions of iron in almandine-composition glass to 91 GPa

Author

Dorfman Susannah, Dutton Sian, Potapkin Vasily, Chumakov Aleksandr, Rueff Jean-Pascal, Chow Paul, Xiao Yumin, Cava Robert, Duffy Thomas, McCammon Catherine, and Gillet Philippe

Subjects
Condensed Matter::Strongly Correlated Electrons
Abstract

Valence and spin states of Fe were investigated in a glass of almandine (Fe3Al2Si3O12) composition to 91 GPa by X ray emission spectroscopy and energy and time domain synchrotron Mössbauer spectroscopy in the diamond anvil cell. Changes in optical properties total spin moment and Mössbauer parameters all occur predominantly between 1 bar and 30 GPa. Over this pressure range the glass changes from translucent brown to opaque and black. The total spin moment of the glass derived from X ray emission spectroscopy decreases by 20. The complementary Mössbauer spectroscopy approaches reveal consistent changes in sites corresponding to 80–90 Fe2+ and 10–20 Fe3+. The high spin Fe2+ doublet exhibits a continuous decrease in isomer shift and increase in line width and asymmetry. A high spin Fe3+ doublet with quadrupole splitting of 1.2 mm/s is replaced by a doublet with quadrupole splitting of 1.9 mm/s a value higher than all previous measurements of high spin Fe3+ and consistent with low spin Fe3+. These observations suggest that Fe3+ in the glass undergoes a continual transition from a high spin to a low spin state between 1 bar and 30 GPa. Almandine glass is not expected to undergo any abrupt transitions in electronic state at deep mantle pressures.

Published
2016

96. Temperature dependence of phonons in Pd_3Fe through the Curie temperature

Author

Yang, F. C., Hellman, O., Lucas, M. S., Smith, H. L., Saunders, C. N., Xiao, Yuming, Chow, Paul, and Fultz, B.

Subjects
Condensed Matter::Materials Science, Condensed Matter::Strongly Correlated Electrons
Abstract

Iron phonon partial densities of states of Pd_3^(57)Fe were measured from room temperature through the Curie transition at 500 K using nuclear resonant inelastic x-ray scattering. The experimental results were compared to ab initio spin-polarized calculations that model the finite-temperature thermodynamic properties of L1_2-ordered Pd_3Fe with stochastically generated atomic displacements, coupled with magnetic special quasirandom structures of noncollinear magnetic moments. The scattering measurements and first-principles calculations show that the Fe partial vibrational entropy is close to what is predicted by the quasiharmonic approximation owing to a cancellation of effects. Anharmonicity and a magnon-phonon interaction approximately cancel a ferromagnetic optical phonon stiffening.

Published
2018

97. HPCAT: A Static Compression Science Sector at the Advance Photon Source

Author

PARK, Changyong, primary, BOMMANNAVAR, Arun S., additional, CHOW, Paul, additional, FERRY, Richard A., additional, HRUBIAK, Rostislav, additional, KENNEY-BENSON, Curtis, additional, MENG, Yue, additional, POPOV, Dmitry, additional, ROD, Eric, additional, SHEN, Guoyin, additional, SMITH, Jesse S., additional, SOMAYAZULU, Maddury S., additional, VELISAVLJEVIC, Nenad, additional, and XIAO, Yuming, additional

Published
2019
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99. Pressure-enhanced interplay between lattice, spin, and charge in the mixed perovskite La2FeMnO6

Author

Li, Nana, primary, Fan, Fengren, additional, Sun, Fei, additional, Wang, Yonggang, additional, Zhao, Yongsheng, additional, Liu, Fengliang, additional, Zhang, Qian, additional, Ikuta, Daijo, additional, Xiao, Yuming, additional, Chow, Paul, additional, Heald, Steve M., additional, Sun, Chengjun, additional, Brewe, Dale, additional, Li, Aiguo, additional, Lü, Xujie, additional, Mao, Ho-kwang, additional, Khomskii, Daniel I., additional, Wu, Hua, additional, and Yang, Wenge, additional

Published
2019
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