大洋板块到底俯冲进地球有多深 - Dr. Jiuhua Chen
APRIL 5, 2017 —
北京高压科学研究中心陈久华研究员与台湾中央研究院謝文斌实验室合作，成功测试了高压下水对橄榄石热导率的影响，发现尽管常压下橄榄石热导率几乎不受水的影响，但在过度带的压力下（十三万大气压以上）橄榄石中的水会使其热导率下降一半。因此俯冲带中的温度会比原来科学家想象更低，橄榄石又可以在过度带生存了。该研究结果“Hydration-reduced lattice thermal conductivity of olivine in Earth's upper mantle”4月3日发表在《美国科学院院报》。
Strong coupling between Weyl fermions and phonons in TaAs - Dr. Bing Xu
APRIL 5, 2017 —
Scientists from HPSTAR and IOP-CAS, in collaboration with Dr. Rohit Prasankumar’s group at LANL, studied the temperature evolution of electronic and phonon properties of the Weyl semimetal TaAs using infrared spectroscopy. They found explicit evidence for strong coupling between an infrared-active A1 phonon and Weyl fermions in TaAs. The study is published in Nature Communications (DOI: 10.1038/ncomms14933)
Unexpected stoichiometry in Sn-Se system - Dr. Kuo Li
MARCH 30, 2017 —
Scientists from HPSTAR and The University of Hong Kong combined in situ synchrotron x-ray diffraction and density functional theory and evolutionary algorithms to examine the high-pressure structural behavior of Sn-Se system. The team observed a new compound with an unexpected stoichiometry in the Sn-Se binary system. The research is published in the March 28th edition of Physical Review Letters.
Pressure-tuned multiferroic KBiFe2O5 - Dr. Ganghua Zhang
MARCH 16, 2017 —
New study from a team of HPSTAR scientists, led by Drs. Ganghua Zhang and Wenge Yang, find that pressure can simultaneously enhance ferroelectric and photoelectric properties of multiferroic KBiFe2O5. These findings may open a new avenue to discovering and designing optimal ferroelectric compounds for solar energy applications. The work was highlighted on the Advanced Electronic Materials cover.
Record pressure squeezes stability of Ar(H2)2- Dr. Cheng Ji
MARCH 15, 2017
— Hydrogen-rich materials have been predicted to be promoters for the metallization of hydrogen. A group of scientists led by HPSTAR director, Dr. Ho-kwang Mao has studied Ar(H2)2, a hydrogen-rich material formed by Argon (Ar) and Hydrogen (H2), to 358 gigapascals— almost the pressure in the inner core of the Earth, by combining experimental and theoretical methods. Contrary to the previous thought, it was observed that Ar damps the intermolecular interactions between H2 molecules, an effect as ‘negative’ chemical pressure which postpones metallization. The results were published in Proceeding of the National Academic of Sciences, USA.
Smaller nanocrystals may not rotate more after all - Dr. Bin Chen
MARCH 2, 2017 —
For more than 60 years, the conventional belief has been that smaller grains of materials rotate more under stress due to the motion of grain boundary (GB) dislocations. Under the guidance of Dr. Bin Chen of the Center for High Pressure Science & Technology Advanced Research (HPSTAR), Xiaoling Zhou, a Ph.D. student of HPSTAR, and her co-workers observed that nanocrystals of a critical grain size rotate more than any other grain size. The results were published today in the journal Physical Review Letters: “Reversal in the Size Dependence of Grain Rotation”.
Fe isotopic fractionation between mantle and metallic core - Dr. Jung-Fu Lin
FEBRUARY 21, 2017 —
Equilibrium iron isotope fractionation is vital to understand the isotopic heterogeneity within the Earth, and therefore useful to reveal Earth’s early history and its geodynamical evolution. New work led by HPSTAR scientists, Dr. Jung-Fu Lin and graduate student Hong Yang, and Dr. Nicolas Dauphas from the University of Chicago found that the equilibrium iron isotope fractionation between silicate and iron at conditions relevant to Earth’s core formation is quite small relative to the observed heavy iron isotope enrichment in terrestrial basalts. This suggests that the interplanetary variability in iron isotopic composition cannot be ascribed to core formation. The work is published by Nature Communications (doi:10.1038/ncomms14377).
Helium chemistry under high pressure - Dr. Xiao Dong
FEBRUARY 07, 2017 —
Although helium is the second (after hydrogen) most abundant element in the universe, it doesn’t play well with others. Now, an international team of researchers, including HPSTAR scientist, Dr. Dongxiao has predicted two stable helium compounds — Na2He and Na2He O. The scientists experimentally confirmed and theoretically explained the stability of Na2He. This work published by Nature Chemistry (DOI:10.1038/nchem.2716), could hold clues about the chemistry occurring inside gas giant planets and possibly even stars, where helium is a major element.
Freeing hydrogen in Earth's lower mantle - Dr. Ho-Kwang Mao
FEBURARY 04, 2017 —
In Earth interior, water (H2O) plays an important role in rock physics but geoscientists rarely treat water in its decomposable forms, like hydrogen plus oxygen. However, new work from a team led by HPSTAR director, Dave Mao, has identified the hydrogen can escape from the water under lower mantle conditions. Their results were published in Proceeding of the National Academic Science, U.S.A.
Exotic two dimensional silica – Dr. Xiao Dong
JANUARY 31, 2017 —
Using computer modeling, scientists from HPSTAR and Tongji University have found out three new forms of 2D-silica with exotic mechanical and electrical properties — large negative Poisson's ratios and widest electric bandgap among all reported 2D materials . They detailed their work in the latest issue of the journal Nano Letters (DOI: 10.1021/acs.nanolett.6b03921).
New Stories for Viologen Materials - Dr. Lin Wang
JANUAR. 23, 2017
Viologen materials have been well known for electrochromism and photochromism from electro and photo stimulus. New work from a team led by Prof. Enqing Gao of East China Normal University and Dr. Lin Wang from hpstar found piezochromis in viologen compounds. This is not only a new chromic phenomena for viologen compounds but also represents the first example of organic mechanochromism and hydrochromism associated with radical formation via electron transfer, proposed in the paper published in the journal Chemical Science (DOI: 10.1039/C6SC04579K).
Exotic ST12-Gemanium - Dr. Duckyoung Kim
JANUARY. 03, 2017 — Scientists at Geophysical Lab, Yanshan University and HPSTAR combined experimental and theoretical methods to probe the exotic properties of one special form-ST12-Ge of the element germanium. The results solve the long-standing debate on the optical and electronic properties of semiconducting Ge and suggest ST12-Ge to be a better material for infrared detection and imaging instead of single-junction solar absorbing.
Origin of ultrahigh piezoelectricity in relaxor-ferroelectrics - Dr. Gang Liu
DECEMBER 21, 2016 —
Over last 60 years, efforts to enhance piezoelectricity generally resort to tuning the long-range ferroelectric phase transition. In the work published in the recent issue of Nature Communications (doi:10.1038/ncomms13807), the researchers revealed that small amount of nanoscale local inhomogeneity may dramatically improve the piezoelectric responses (50-80%) of a ferroelectric crystal.
Pressure realized bandgap requirement by Shockley-Queisser limit in FAPbI3 - Dr. Gang Liu & Dr. Ho-Kwang Mao
DECEMBER 6, 2016 —
For the first time, scientists have reached the Shockley-Queisser theory optimized bandgap for single-junction solar cells in lead-based perovskites. A new study led by HPSTAR scientists Dr. Gang Liu and Dr. Dave Mao, report an unprecedentedly tuned bandgap of the Shockley–Queisser limit and double-prolonged carrier lifetime in formamidinium lead triiodide (HC(NH2)2PbI3) in the latest issue of Advanced Functional Materials (DOI: 10.1002/adfm.201604208).
Cooperative spin-crossover under pressure - Dr. Wenge Yang
DECEMBER 5, 2016 —
A joint team of researchers from UNLV, HPSynC and HPSTAR reported their breakthrough in pursuing "cooperative" pressure-driven SCO in J. Am. Chem. Soc. (DOI: 10.1021/jacs.6b10225). An abrupt pressure-driven SCO accompanying with large lattice collapses and semiconductor-to-metal transitions was achieved in two-dimensional honeycomb lattices, MnPS3 and MnPSe3, for the first time. The work opens a new avenue for the exploration of pressure-responsive multifunctional materials.
Possible coexistence of superconductivity and superhardness in BeB6- Dr. Huiyang Gou
NOVEMBER 21, 2016 —
New work co-led by HPSTAR scientist, Dr. Huiyang Gou, theoretically predicts the structural and physical properties of beryllium hexaboride (BeB6) at ambient and high pressures. The ambient phase of BeB6 shows a Vicker's hardness comparable to that of γ-B/cBN and coexists with superconductivity, which is unusual and exciting. This study provides new insights into the bonding mechanism for design and synthesis of novel functional materials
Formation of Xenon-Nitrogen Compounds at High Pressure - Dr. Ross Howie
OCTOBER 17, 2016 –
A group led by HPSTAR scientist Dr Ross Howie and including Dr Jack Binns (RTH Lab) and Dr Phillip Dalladay-Simpson (CEP), in collaboration with researchers from CSEC (Edinburgh, UK) used high pressures to explore the possibility of forcing two of the more unreactive elements of the periodic table, xenon and nitrogen, to react. Joint investigation by X-ray diffraction and Raman spectroscopy showed the formation of a novel van der Waals compound at pressures as low as 5 GPa. After transformation to a lower symmetry phase this material, Xe(N2)2, remains remarkably stable up to at least 180 GPa and temperatures of 2000 K. This study is published in the journal Scientific Reports (doi:10.1038/srep34896).
FeSe: What is the consensus on its gap structure? - Dr. Mahmoud Abdel-Hafiez
OCTOBER 9, 2016 —
By the in situ angle resolved photoemission spectroscopy (ARPES) measurements on an excellent quality of FeSe single crystal, an international joint team co-led by Dr. Mahmoud Abdel-Hafiez from HPSTAR, realized that the superconducting gap shows a pronounced twofold anisotropy around the elliptical hole pocket near Z (0, 0, π), with gap minima at the end points of its major axis. The study is published in the journal Phys. Rev. Lett. (DOI: 10.1103/PhysRevLett.117.157003 ).
New Weyl semimetal phase in TaAs – Dr. Wenge Yang
SEPTEMBER 30, 2016 —
A joint team co-led by HPSTAR scientist Wenge Yang studied the envolution of electronic and structural properties of Weyl semimetal TaAs using multiple methods. They found a pressure-induced new Weyl semimetallic phase with isoenergetic 12 Weyl nodes in TaAs. The study is published in the journal Physical Reviews Letters (DOI:https://doi.org/10.1103/PhysRevLett.117.146402).
Deformation Behavior across the Zircon-Scheelite Phase Transition - Drs. Fang Hong & Bin Chen
SEPTEMBER 23, 2016 —
Dynamic flow and stress information may be reconstructed from materials’ preferred orientations. Recent experimental work from a team of HPSTAR scientists led by Drs. Fang Hong and Bin Chen, show that the high-pressure mineral Scheelite can inherit texture from its lower-pressure Zircon phase, suggesting new ways of interpreting flow in the upper mantle and transition zone. The study is published in the journal Phys. Rev. Lett. (DOI: 10.1103/PhysRevLett.117.135701).
More stable perovskite solar cell treated by pressure - Drs. Qiangyang Hu and Wenge Yang
SEPTEMBER 9, 2016 —
As part of a team led by Dr. Xujie Lü from Los Alamos National Laboratory, HPSTAR scientists Dr. Qingyang Hu and Dr. Wenge Yang recently conducted the first comparative study of a lead-free tin halide perovskite, CH3NH3SnI3, before and after high-pressure treatment up to 30 GPa at HPCAT. It became more stable after high-pressure treatment, with a three-fold increase in electrical conductivity and enhanced light absorption.
Fluids-dependent High-pressure Chemistry of ZIF-8 - Dr. Yongjae Lee
SEPTEMBER 8, 2016 —
New work published in JACS (DOI: 10.1021/jacs.6b07374) by HPSTAR scientist, Yongjae Lee and Junhyuck Im of Yonsei University, Narae Yim and Jaheon Kim of Soongsil University, and Thomas Vogt of University of South Carolina, found clear fluids-dependent pressure-induced insertion in ZIF-8. This study suggests that the future studies of the high pressure chemistry of ZIFs and other MOFs should consider guest-host interactions under pressure.
Pressure induced Polymerization and metaliztion of CaC2 - Drs. Haiyan Zheng & Kuo Li
AUGUST 30, 2016 —
Transformation between different types of carbon–carbon bonding in carbides often results in dramatic changes of physical and chemical properties. New work from a team led by scientists from HPSTAR, Drs. Haiyan Zheng and Kuo Li has given a systematical investigation on CaC2 under external pressure from multiple techniques and found linear acetylide anions will polymerize into cyclic ribbons structure, accompanying with more than 107 folds enhancement in the conductivity. The journal Chemical Science has published an article featuring the results of the study (DOI: 10.1039/c6sc02830f).
C-H bond activated by high pressure in Acetonitrile - Drs. Haiyan Zheng and Kuo Li
AUGUST 29, 2016 —
Acetonitrile (CH3CN) is the simplest and one of the most stable nitriles. It is well known that the reaction usually occur on the CN triple bond rather than the inert C-H bond. New work from a team of HPSTAR scientists co-led by Drs. Haiyan Zheng and Kuo Li found that the C-H bond can be activated by the cyano group under high pressure. The hydrogen atom transfers from the CH3 to CN along the CH...N hydrogen bond which produces an amino group and initiates the polymerization. This stories is published in Angew. Chem Int. Ed. (doi: 10.1002/anie.201606198).
Pressure-driven cooperative spin and lattice collapses in Mn(II) Chalcogenides - Dr. Wenge Yang
AUGUST 2, 2016 —
Recently, giant pressure-driven volume collapse (> 20%), a rarely reported phenomenon in condensed matter, was observed in MnS2 and MnS. The intriguing behavior was considered to be associated with the pressure-driven high-spin to low-spin transition of Mn(II), but lacking experimental evidences and in-depth understandings. An international team — UNLV, HPSynC and HPSTAR of scientists co-led by Dr. Wenge Yang dug into this phenomenon and found that the giant volume collapse was coupled with the spin state transition of Mn(II) and a semiconductor-to-metal transition. This work is published online in Angew. Chem Int. Ed., 2016, doi:10.1002/anie.201605410.
Observation of sodium polyhydrides under pressure- Drs Duckyoung Kim & Ho-Kwang Mao
JULY 29, 2016 — Combining synchrotron x-ray diffraction and Raman spectroscopy, a team co-led by HPSTAR scientist, Duckyoung Kim, report the first observation of formation of sodium polyhydrides (NaH3 and NaH7) between two diamond tips. These results are applicable to the design of new energetic solids and high-temperature superconductors based on hydrogen rich materials. These findings were reported in Nature Communications.
Band-gap narrowing together with carrier-lifetime prolongation in organic-inorganic trihalide perovskite – Drs Lingping Kong and Gang Liu
JULY 25, 2016 —
A team of HPSTAR scientists led by Dr. Gang Liu utilized high-pressure technique to tune the electrical and photovoltaic performance in organic-inorganic hybride perovskites. 70%-100% carrier-lifetime increasing was found in mildly compressed organic-inorganic trihalide perovskite together with bad-gap narrowing. The story is just published on the July 21th edition of PNAS
Why is the simplest Fe-based superconductor the strangest? - Drs. Mahmoud Abdel-Hafiez and Xiaojia Chen
JULY 20, 2016 —
By the in situ ARPES and a series of thermodynamic measurements, an international joint team co-led by Drs. Mahmoud Abdel-Hafiez and Xiaojia Chen from HPSTAR, realized a hump at elevated temperatures around 280K seems to be a standard feature of any degenerated semiconductors observed many times in various systems. This hump reflects the crossover between semiconducting and metallic behavior. Inelastic neutron-scattering experiments reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K in FeSe. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. These stories are published in the July 19th edition of Nature Communications and in June 8th edition of Phys. Rev. B.
Reversible bi-metastable phase switching in the VO2 system - Dr. Wenge Yang
JULY 18, 2016 —
By using the in situ synchrotron techniques at HPCAT and a series of self-designed experiments, an international joint team co-led by Dr. Wenge Yang from HPSTAR, realized a controllable phase switching between pressured-induced amorphization and thermal-driven recrytallization in VO2(B) nanosheets. They claimed that it was the ﬁrst ever example of a structural memory effect observed in a strongly correlated material. The story is published in the July 18th edition of Nature Communications (doi:10.1038/ncomms12214).
Electron-rotor interaction in Organic-Inorganic Lead Iodide Perovskites - Dr. Gang Liu
JULY 14, 2016 —
New work co-led by Dr. Gangliu from HPSTAR found carrier-rotor coupling effect in perovskite organic-inorganic hybrid lead iodide (CH3NH3PbI3) compounds from isotope effect. The discovery of the electron-rotor interaction would help to establish the theoretical foundation governing various energy transport, conversion, and storage sciences. The story is published in The Journal of Physical Chemistry Letters.
Pressure-induced heavy doping in the graphene/MoS2 heterostructure – Dr. Jungfu Lin
JUNE 21, 2016 — New work coauthored by HPSTAR scientist, Jungfu "Afu" Lin, found a unique way- hydrostatic pressure for achieving controllable charge transfer doping in the graphene/MoS2 heterostructure. This research sheds light on how modification of interactions in a heterostructure under pressure can lead to many fold enhancements in carrier concentration of graphene. The story is published in Small.
A new form of iron oxide controls hydrogen and oxygen cycles in the Earth interior - Dr. Ho-Kwang Mao
JUNE 9, 2016 — We breathe oxygen every day, but we might not know the Earth interior keeps approximately one million times oxygen more than the atmosphere. A team of HPSTAR scientists led by Ho-Kwang "Dave" Mao has discovered a new form of iron oxide - FeO2 that holds unprecedentedly large amount of oxygen, forming when the subducting plates carry the common “rust” (FeOOH) down into the deep mantle and controlling the flow of hydrogen and oxygen cycles in the Earth interior. Their findings are published in the June 9, 2016 issue of the journal Nature.
Squeeze electrons by diamond anvils: Discovery of a novel confined metal at high pressure - Dr. Yang Ding
MAY 25, 2016 —
Insulator-metal transition (IMT), where a system changes from insulator to metal with a largely enhanced electrical conductivity, represents an important topic in contemporary condensed matter physics. New study led by scientist Dr. Yang Ding from Center for High Pressure Science and Technology (HPSTAR) found that the material Sr3Ir2O7 undergoes an IMT and becomes a confined metal at high pressure, showing metallicity in the crystal ab-plane but insulating along the c-axis. Such unusual phenomenon resembles the strange metal phase in cuprate high-temperature superconductors. This novel discovery opens up a new field for synthesizing functional materials. The work is published this week in Physical Review Letters.
Pressure-dependent isotopic composition of iron alloys - Dr. Wendy Mao and Dr. Jinfu Shu
APRIL 28, 2016 —
New work from a research team co-authored by Dr. Jinfu Shu from HPSTAR and Dr. Wendy Mao from Stanford University and HPATAR, shows some unexpected findings about iron chemistry under high-pressure conditions, such as those likely found in the Earth’s core, where iron predominates and creates our planet’s life-shielding magnetic field. Their work published in the journal Science, could shed light on Earth’s early days when the core was formed through a process called differentiation—when the denser materials, like iron, sunk inward toward the center, creating the layered composition the planet has today
Superconductivity at 46 K in FeSe - Dr. Mahmoud Abdel-Hafiez
FeSe and doped FeSe exhibit intriguing and distinctive properties, which are currently the research focus in the field of high temperature superconductors. Undoped FeSe possesses a nematic order below 90 K and superconductivity of 8 K. The most mysterious property here is not even the pressure or strain induced Tc increase, but a giant enhancement of the superconductivity at the FeSe/SrTiO3 interface, where SrTiO3 (STO) has nothing in common with magnetic interaction. It seems that STO provides phonons that enhance superconductivity in single-layered FeSe. International collaborations including HPSTAR physicist, Dr. Mahmoud Abdel-Hafiez, gave a systematic study in doping controlled FeSe system, proposing that the enhanced superconductivity is independent of the thickness of FeSe while intrinsic to FeSe. However, it is under heated debate whether the nematic order, below 90 K in FeSe, is driven by spin or orbital fluctuations. These issues in FeSe superconductors have been published this year in Nat. Mater. 15, 159 Nat. Mater. 15, 159 (2016), recently in Nat. Comm. 7, 10840 (2016), and last year in Phys. Rev. B 91, 165109 (2015).
Superconductivity in ZrTe5 under compression - Dr. Wenge Yang & Dave Mao
MARCH 2, 2016
— By multiple complementary methods, new work co-led by scientists from HPSTAR, Dr. Wenge Yang, and Dr. Dave Mao, are trying to investigate possible crystal structural as well as electronic transitions in 3D topological material ZrTe5 under compression. Two pressure induced superconducting phases are found in ZrTe5. And in situ high-pressure synchrotron X-ray diffraction and Raman spectroscopy together with theoretical calculations indicate that the two-state superconducting phases are correlated to two different crystal structural transitions at corresponding pressures.
From metal to insulator in dense CLi4 - Dr. Dave Mao
MARCH 1, 2016 —
As a contrasting counterpart, lithium compounds may share some similar unexpected behaviors compared with hydrogen dominated materials at high pressures. New work co-led by HPSTAR scientist, Dr. Dave Mao, found that CLi4 becomes progressively less conductive and eventually insulating upon compression based on ab initio density-functional theory calculations.
Lithiation-induced stress in Li-ion batteries from micro-Raman Spectroscopy - Dr. Zhidan Zeng
FEBRUARY 25, 2016 — Stress is along standing challenge for the applications of silicon(Si) anodes in lithium(Li)ion batteries. Using in situ micro Raman spectroscopy, a team of scientists led by Dr. Zhidan Zeng at the Center for High Pressure Science & Technology Advanced Research (HPSTAR) measured the stress in silicon nanoparticles in a working Li-ion battery for the first time. This new study would be helpful in understanding how the nanostructured silicon anodes fracture during battery operation, and therefore provide guidance for their future design.
In-situ crystal structure determination of a minor phase in a multiphase system at megabar pressure - Dr. Li Zhang
FEBRUARY 16, 2016 — Multiple phases often coexist in a polycrystalline sample as a result of phase equilibrium in high-pressure petrological studies. Seifertite SiO2 likely exists as a minor phase near the Earth’s core-mantle boundary (CMB). Structure determination of a minor phase in a sample contained in a diamond anvil cell (DAC) has never been impossible using conventional powder or single crystal diffraction techniques. Utilizing the multigrain crystallography and newly developed procedures, new work led by HPSTAR scientists, Li Zhang et al., has overcome the difficulties and obtained the first in-situ single-crystal structure of seifertite being a minor phase in a polycrystalline sample at 129 GPa (Am. Mineral. 101, 231–234, 2016).
A general structural-property relationship in metallic glass - Charles Zeng
FEBRUARY 1, 2016 — Structure-property relationship is a central topic in materials science. In crystalline materials, the well-defined lattice structure or defects enable us to describe their properties quantitatively. The structure of glass is basically featureless, very few rigorous laws are currently known for defining its ‘disordered’ structure. Establishing general and exact rules regarding structure-property relationships in glass remain elusive. A breakthrough has been made by a international team led by Dr. Qiaoshi Zeng, a staff scientist from HPSTAR. This team established a general rule correlating the bulk properties (volume V) with most prominent atomic structure information (principle diffraction peak position q1) for metallic glasses, i.e. V∝(1/q1)2.5. It is shown that the 2.5 power law is strictly followed by any metallic glass with its volume tuned by pressure and/or composition. This general 2.5 power law is attributed to the well constrained structure change/modification inevitably happened during pressure and/or composition tuning of metallic glasses, which brings new insight into the structure of metallic glasses. These results are just published by PNAS.
Dissociation products and structures of solid H2S - Dr. Lin Wang
JANUARY 11, 2016 — A record of highest critical temperature (Tc) of about 200 K — a temperature that actually exists on Earth’s surface, reported in H2S has lit a fire in superconductivity. This major breakthrough in superconductivity suggest that so high Tc is most likely due to the decomposition product, H3S, which was predicted to have the comparative value in Tc at high pressure. These proposals bring the decompositions conducts of H2S to another hot research topic. New study including Lin Wang, Yanwei Huang and Wentao Li, scientists from HPSTAR, utalizing experimental and theoretical simulations to probe decompositions of compressed H2S and possible stable structures, find that H4S3 is the major component of the dissociation products while there is just a small fraction of H3S.
Lower-mantle materials under pressure - Dr. Jiuhua Chen
JANUARY 8, 2016 — In today’s issue of Science, Dr. Jiuhua Chen from HPSTAR published his Science Perspective paper entitled Lower mantle materials under pressure. In this paper, he proposed a hybrid mantle convection model: a mixture of layered and whole mantle circulations of minerals inside the Earth based on the most recent experimental data and accumulated observational results of geophysics.
Glimpse of metallic hydrogen - Dr. Ross Howie
JANUARY 7, 2016 — Driven by the predication of metallic hydrogen, the first and simplest element, there has been 80 years’ worth of combined theoretical and experimental effort to try to reach this predicted state in hydrogen.
New breakthrough work from a team including Philip Dalladay-Simpson, and Ross T. Howie, two new scientists of HPSTAR, have carried out static compression on hydrogen and its isotopes above 380 gigapascals; higher pressure than any previous study. The work indicates another new phase, phase V, is detected in both hydrogen and hydrogen deuteride at pressures above 325 gigapascals at room temperature. Phase V could provide a glimpse of the theoretical predicated metallic hydrogen. This breakthrough discovery is published on January 07, 2016, in Nature.
Behind Electron Binding in Iron-based Superconductors - Dr. Mahmoud Abdel-Hafiez and Dr. Xiao-Jia Chen
DECEMBER 7, 2015 — International collaborations including HPSTAR physicists (Dr. Mahmoud Abdel-Hafiez and Prof. Xiao-Jia Chen) have studied one member of the recently discovered family of superconductors based on iron compounds and find this exotic form of superconductivity to have complex, multi-gap character. Additionally, the interplay between spin fluctuations, nematicity and superconductivity is well reported. A fact of principal importance for understanding the mechanisms of superconductivity is that the superconducting gap width never becomes zero around the constant-energy Fermi surface. Results of this work were published in two of the leading physical journals of the world, Physical Review B and Nature Material. Multiple techniques, in particular; specific heat, magnetization, transport, penetration depth, scanning tunneling microscopy and neutron scattering, have been used to achieve these studies.
Anomalous compression in CrAs - Dr. Lin Wang
NOVEMBER 17, 2015 — Using synchrotron X-ray diffraction combined with theoretical modeling, a team led by scientists from HPSTAR, Drs. ZhenhaiYu, Qingyang Hu, Chunyu Li, and Lin Wang performed detailed structure study on CrAs, an important bulk superconductivity material, at high pressures. They observed anomalous anisotropy with a pressure-induced isostructural transition. This crystal change agrees well with the conditions at which bulk CrAs becoming superconducting. The results shed light on the structural and related electronic responses to highpressure, which play a key role toward understanding the superconductivity ofCrAs. Their findings are published by recent PNAS (“Anomalous anisotropic compression behavior of superconducting CrAs under high pressure,” doi:10.1073/pnas.1520570112).
Different structure evolution in Bi2Se3 - Lin Wang
NOVEMBER 2, 2015 — Dr. Lin Wang and Zhenhai Yu from HPSTAR, led an international group of collaborators, found two pressure-induced structural phase transitions in topological insulator, Bi2Se3 in their recent study, which follows differently in the structure transformation compared with its isostructural compounds, Bi2Te3 and Sb2Te3.
Reversed resistivity change in GST - Dr. Lin Wang
OCTOBER 29, 2015 — Solid-state materials can be categorized by their ordering levels into crystalline, amorphous, quasi-crystalline, and crystalline but containing amorphous unites phases. Crystalline and amorphous materials are two most common matters in condensed-matter physics and materials science. Under ambient conditions, it is well known that the amorphous phase normally exhibits a higher resistivity, exceeding its crystalline counterpart by 2–5 orders of magnitude. New study indicated that such pronounced resistivity contrast is remarkably reduced and even reversed with increasing hydrostatic-like pressure in the prototypicalphase-change material GeSb2Te4 (GST).
Deformation twinning in silver nanocrystal - Dr. Wege Yang
OCTOBER 20, 2015 — There are many difficult challenges to track the deformation process in a single nanoscale crystal under external stresses. New research co-led by scientist from HPSTAR, Dr. Wenge Yang provides an in situ three-dimensional mapping of morphology and strain evolutions in a single-crystal silver nanocube under high-pressure conditions using coherent diffraction imaging (CDI) method.
Biologic carbon found in 4.1 billion-year-old zirzon - Wendy Mao
A set of 47 human teeth found in China dated to 80,000-120,000-years-old, described in a paper published on October 14, 2015, in Nature, bear a close resemblance to those seen in modern humans. Then another study co-authored by Wendy Mao, a scientist of HPSTAR, also indicates evidence of life on earth from the carbon isotopes in 4.1 billion-year-old ziron crystals. The research was published recently in PNAS. These evidence of life may rewrite early earth history as well as human history.
Metallic glass: homogenous in appearance, fractal at heart - Dr. Qiaoshi Zeng & Dr. Wendy Mao
SEPTEMBER 18, 2015 — The atomic structure of glasses has been a long-standing unsolved mystery in condensed mater physics and materials science. A breakthrough in understanding the atomic structure of an important new category of glass — metallic glasses was made by a joint research team including staff scientists of HPSTAR, Dr. Qiaoshi Zeng and Dr. Wendy L. Mao. From multiple techniques, the team found that a specific fractal model — the percolation cluster packing could provide a perfect explanation of the 2.5 power law observed in the compression experiments of metallic glasses and a unified description of the atomic structure of metallic glasses from short range to macroscopic length scale for the first time. These results are just published by Science (DOI: 10.1126/science.aab1233).
Watching laser-shocked stishovite grow from amorphous silica in nanoseconds – Dr. Wenge Yang & Dr. Wendy Mao
SEPTEMBER 4, 2015 — Phase transitions have long been studied for centuries but little is known about the processes by which the atoms rearrange. New work from a team including HPSTAR scientists, Dr. Wenge Yang and Dr. Wendy Mao, performed in situ pump – probe x-ray diffraction measurements on shock-compressed fused silica, revealing the evolution of an amorphous to crystalline high pressure stishovite phase transition in nanoseconds. This is the first observation of shock-induced nucleation and growth of a high-pressure crystalline phase from an initially amorphous material. The study is published in recent Nature Communications (DOI: 10.1038/ncomms9191).
Anomalous Photovoltaic Response in CH3NH3PbBr3 – Dr. Wenge Yang
AUGUST 15, 2015 — The performance of solar cell newcomer materials called halide pervoskite has soared in recent years, which has rapidly surpassed that of both conventional dye-sensitized and organic photovoltaics. A recent research from a team of scientists including HPSTAR scientists Dr. Wenge Yang, Dr. Liuxiang Yang, Ms. Xiangting Ren and Dr. Lin Wang, using in situ high-pressure techniques to investigate the photovoltaic properties of organolead bromide perovskite CH3NH3PbBr3, found anomalous photovoltaic response associated with the pressure-induced phase transitions and reversible amorphization.
CMR induced in pure lanthanum manganite - Dr. Ho-Kwang Mao
AUGUST 12, 2015 — Colossal magnetoresistance (CMR) is a property with practical applications in a wide array of electronic tools including magnetic sensors and magnetic RAM. New research from a team including HPSTAR director Dr. Ho-Kwang “Dave” Mao, used high-pressure techniques to induce CMR for the first time in a pure sample, lanthanum manganite, LaMnO3.
Semiconductor - metal in multilayered tungsten disulfide - Dr. Jung-fu Lin
AUGUST 11, 2015 — Tungsten disulphide (WS2) is a layered transition metal dichalcogenide that has recently raised considerable interest due to its unique electronic properties among transition metal dichalcogenide family compounds. A team of scientists at HPSTAR, the University of Texas at Austin, GeorgeWashington University, Chinese Academy of Sciences respectively, together with collaborators, has found a semiconductor to a metal transition in WS2 at high pressures. This new result could help in the development of electronically tuneable devices to enhance mobility in pressure electronics.
Pressure induced metallization without structural transition in layered MoSe2 - Dr. Qiaoshi Zeng
JUNE 19, 2015
—The electronic structure transition (insulator to metal or semiconductor to metal transition) is generally accompanied or followed by a first-orderstructural transition. However, using multiple experimental techniques and ab-initio calculatios, new research from a group including Qiaoshi Zeng from HPSTAR find that the metallization process does not involve any crystal structure change in MoSe2, which allows its energy continuous tunability for potential opto-electronic or photovoltaic applications. Their work is published on recent Nature Communications (DOI: 10.1038/ncomms8312).
A promising novel phase for silicon anode lithium-ion battery - Dr. Zhidan Zeng
APRIL 14, 2015 — A team led by Dr. Zhidan Zeng at the Center for High Pressure Science & Technology Advanced Research (HPSTAR) synthesizes a new phase of Li15Si4 (beta-Li15Si4) under pressure. This beta-Li15Si4 phase shows higher packing density and superior mechanical properties than alpha-Li15Si4. This provides a new perspective on how to overcome the long-standing challenge in the application of silicon anodes for lithium-ion batteries.
Silica: Multiple Phases, other than a glassy structure - Qingyang Hu
MARCH 24, 2015
— Using synchrotron x-ray diffraction and theoretical modeling, the team from the Center for High Pressure Science & Technology Advanced Research (HPSTAR) including Qingyang Hu, Wenge Yang, Howard Sheng, and Ho-kwang Mao discovers four previously unknown phases of silicon dioxide, shedding light on the silica compression mechanism at room temperature. Their findings are published by Nature Communications (“Polymorphic phase transition mechanism of compressed coesite,” 6, 6630. DOI: 10.1038/ncomms7630).
Pressure induced seemed phase transition in metallic glass along with abnormal thermal expansions - Dr. Dawei Fan
FEBRUARY 2, 2015 — A team of scientists including Dr. Dawei Fan from HPSTAR, discovered a seemed first-order phase transition in Ce-based metallic glass along with abnormal thermal expansion at high pressure. This work indicate that pressure will be a very effctive method for investigating the structure or improving performance of metallic glasses for future applications.The related work is published on Nature Communications (“Hierarchical densification and negative thermal expansion in Ce-based metallic glass under high pressure”, DOI:10.1038/ncomms6703).
Elusive Hot Hydrogen Leads To More Pressing Questions - Dr. Ross Howie
MARCH 3, 2015 —
Scientific studies of hydrogen at extreme pressures and temperatures are crucial for understanding the rich variety of unusual states and structures, and strange properties, that dense hydrogen demonstrates. But the combination of high pressures with moderate temperatures (>200 GPa and 550 – 1,300 K) has long been an experimentally inaccessible "no man's land" for hydrogen. Publishing in Nature Materials (DOI: 10.1038/NMAT4213), Dr. Ross Howie, a new Associate Staff Scientist who is joining HPSTAR in 2015, and co-workers at the University of Edinburgh have demonstrated now to overcome this difficulty (>200 GPa and 550 – 1,300 K), allowing them to observe a new, dense form of hydrogen, possibly a liquid phase at unusually low temperature.
Losses in Ferroelectric Materials - Dr. Gang Liu
Shanghai, February 14, 2015—Energy loss (or energy dissipation) is one of most critical issues in ferroelectric materials for engineer applications. This loss including elastic, piezoelectric and dielectric, associated with elasticity,dielectric relaxation and piezoelectric hysteresis in ferroelectrics, have involved many controversies/confusions in the past several decades. In a newly published study led by Dr. Gang Liu from Center of High Pressure Science and Technology Advanced Research, reviewed how the energy losses happened in ferroelectrics, fully tracked the origin of energy losses, and proposed a general theoretical model to describe the inherent relationships among elastic, dielectric, piezoelectric and mechanical losses.
Pressure-Dependent Electronic and Structural Properties of MoS2 - Dr. Jung-Fu Lin
Scientific Achievement: The direct optical band gap of the monolayer 2H-MoS2 increases by 11.7% from 1.85 eV to 2.08 eV up to 16 GPa. DFT calculations further show metallization at ~60 GPa.
A new phase in the deep lower mantle - Dr. Li Zhang
Utilizing a suite of latest advanced techniques, the research team from the Center for High Pressure Science and Technology Advanced Research (HPSTAR) reported a surprising discovery in mineral physics: Fe-bearing perovskite, which was considered as the major component in the lower mantle, is found to be unstable in the bottom third of the lower mantle. Therefore, the constitution of the lower mantle may be significantly different than previously thought. These results are published by Science on May 23, 2014.
A universal fractional noncubic power law for density in metallic glasses - Dr. Qiaoshi Zeng
Tuning with pressure, a research team led by Dr. Qiaoshi Zeng with collaborators from HPSTAR, Stanford University, SLAC National Accelerator Laboratory, and Geophysical Laboratory at Carnegie Institution of Washington made a surprising discovery that the three-dimensional density of metallic glasses is not simply the cube of their one-dimensional average interatomic spacing, but varies with a universal 5/2 fractional power. The result is published by Phys. Rev. Lett. on May 8, 2014.
Detecting Grain Rotation at the Nanoscale - Dr. Bin Chen
An international team of researchers, led by HPSTAR scientist Bin Chen have now succeeded in observing nano-scale plastic deformation by collecting x-ray diffraction (XRD) on poly-crystalline metal samples under high pressure in a radial diamond anvil cell (r-DAC). PNAS [PNAS 111 3350 ( 2014)]
Coherent diffraction imaging of nanoscale strainevolution in a single crystal under high pressure - Dr. Wenge Yang
Recently, a research group, led by Dr. Wenge Yang, a scientist of HPSTAR and Carnegie Institution of Washington, studied the Nano-size Effect in gold nano-particles under very high pressures. This research, published in the Nature Communications, is one of the first works that shows nanometer resolution imaging of a material in real conditions, and in real time.
Single-crystal structure of (Mg,Fe)SiO3 postperovskite in Earth D" layer - Dr. Li Zhang, Dr. Wenge Yang, Dr. Ho-Kwang Mao
Using a novel method for high-pressure single-crystal study, HPSTAR scientist Li Zhang, Wenge Yang ,and Ho-kwang Mao, in collaboration with Meng Yue (HPCAT), Wendy Mao (Stanford) and colleagues from the University of Chicago have obtained the very first single-crystal structure of (Mg,Fe)SiO3 post-perovskite phase under high pressure corresponding to the condition in the Earth’s D′′ layer. This result is published by PNAS.
Probing the Lower Size Limit of Dislocation Activity - Dr. Bin Chen
In a study by researchers of Lawrence Berkeley National Laboratory and several other multiple institutions including HPSTAR, nano-crystals of nickel subjected to high pressure were found to suffer dislocation-mediated plastic deformation even when the crystals were only three nanometers in size. "Our results demonstrate that dislocation-mediated deformation persists to smaller crystal sizes than anticipated". Bin Chen, a materials scientist of ALS and HPSTAR says. These results are published on Science.