Effect of high‐energy light‐ion irradiation on SI‐GaAs and GaAs:Cr as observed by Raman spectroscopy

The structural evolutions of high‐energy (50 MeV) lithium ion (Li³⁺) irradiated undoped semi‐insulating GaAs (SI‐GaAs) and chromium‐doped SI‐GaAs (GaAs:Cr) were investigated by Raman measurements. It is shown that high‐energy Li³⁺ irradiation causes amorphization beyond a fluence of 3 × 10¹³ ions/cm² in undoped SI‐GaAs. Interestingly, the same fluence of ions does not seem to affect the crystallinity in GaAs:Cr appreciably. The effect of ion irradiation on the change in lattice ordering and anharmonicity of the phonon modes of undoped SI‐GaAs and GaAs:Cr is also compared. Copyright © 2011 John Wiley & Sons, Ltd.     

Structures and phase transitions of ScH3 under high pressure

The structures and the phase transitions of ScH3 under high pressure are investigated using first-principles calculations. The calculated structural parameters at zero pressure agree well with the available experimental data. With increasing pressure, the transition sequence hcp (GdH3 -type)→ C2/m →fcc→hcp (YH3-type)→Cmcm of ScH3 is predicted first; the corresponding transition pressures at 0 K are 23 GPa, 25 GPa, 348 GPa, and 477 GPa, respectively. The C2/m symmetry structure is a possible candidate but not a good one as the intermediate state from hexagonal to cubic in ScH3 . On the other hand, via the analysis of the structures of hexagonal ScH2.9 , cubic ScH3 , and cubic ScH2 , we find that the repulsive interactions of H-H atoms must play an important role in the transition from hexagonal to cubic.     

Controllable synthesis of fullerene nano/microcrystals and their structural transformation induced by high pressure

Fullerene molecules are interesting materials because of their unique structures and properties in mechanical, electrical, magnetic, and optical aspects. Current research is focusing on the construction of well-defined fullerene nano/microcrystals that possess desirable structures and morphologies. Further tuning the intermolecular interaction of the fullerene nano/microcrystals by use of pressure is an efficient way to modify their structures and properties, such as creation of nanoscale polymer structures and new hybrid materials, which expands the potential of such nanoscale materials for di- rect device components. In this paper, we review our recent progress in the construction of fullerene nanostructures and their structural transformation induced by high pressure. Fullerene nano/microcrystals with controllable size, morphology and structure have been synthesized through the self-assembly of fullerene molecules by a solvent-assisted method. By virtue of high pressure, the structures, components, and intermolecular interactions of the assemblied fullerene nano/microcrystals can be finely tuned, thereby modifying the optical and electronic properties of the nanostructures. Several examples on high pressure induced novel structural phase transition in typical fullerene nanocrystals with C60 or C70 cage serving as build- ing blocks are presented, including high pressure induced amorphization of the nanocrystals and their bulk moduli, high pressure and high temperature （HPHT） induced polymerization in C60 nanocrystals, pressure tuned reversible polymeriza- tion in ferrocene-doped C60/C70 single crystal, as well as unique long-range ordered crystal with amorphous nanoclusters serving as building blocks in solvated C60 crystals, which brings new physical insight into the understanding of order and disorder concept and new approaches to the design of superhard carbon materials. The nanosize and morphology effects on the transformations of fullerene nanocrystals have also been discussed. These results provide the foundation for the fabrication of pre-designed and controllable geometries, which is critical in fullerenes and relevant materials for designing nanometer-scale electronic, optical, and other devices.     

Elastic properties of alkaline earth oxides under high pressure

In this article, we have investigated the high-pressure structural phase transition of alkaline earth oxides using the three-body potential (TBP) model. Phase transition pressures are associated with elastic constants. An effective inter-ionic interaction potential (TBP) with long-range Coulomb interactions and the Hafemeister–Flygare type short-range overlap repulsion and the vdWl interaction is developed. The present calculations have revealed reasonably good agreement with the available experimental data on structural transition (B1–B2 structure). The phase transition pressures Pt of MgO, CaO, SrO, and BaO occur at 220, 45, 40, and 100?GPa, respectively. Further, the variations of the second-order elastic constants with pressure have followed a systematic trend, which are almost identical to those exhibited by the observed data measured for other semiconducting compounds with rocksalt (B1)-type crystal structure. It is found that TBP promises that we would be able to predict phase transition pressure and elastic constants for other chalcogenides as well. The results may be useful for geophysical study.     

强流脉冲离子束辐照对不锈钢耐腐蚀性能的影响

利用强流脉冲离子束（HIPIB）对316L不锈钢进行了表面辐照处理,研究了HIPIB辐照对其在0.5mol/L H2SO4溶液中电化学腐蚀性能的影响。极化曲线测量结果表明,HIPIB辐照能够显著提高316L的抗腐蚀性能,自腐蚀电流对辐照次数的依赖性与自腐蚀电位相比明显较强。采用扫描电子显微镜（SEM）、X射线衍射（XRD）和电子探针（EPMA）分析辐照后试样表面形貌、表面层相结构和元素分布的变化。结果表明：HIPIB辐照使试样表面光滑化,表面层产生择优取向,且发生了杂质元素的选择性烧蚀,是316L不锈钢耐电化学腐蚀性能得以提高的主要原因。     

Generation of ultra-intense ion beams by a short-pulse laser

This paper summarizes briefly the main experimental and numerical results of the IPPLM team studies on the generation of ultra-intense ion beams by a short (≤1?ps) laser pulse. Basic laser-driven ion acceleration schemes capable of generating such ion beams are described including the target normal sheath acceleration (TNSA) scheme, the skin-layer ponderomotive acceleration (SLPA) scheme and the laser-induced cavity pressure acceleration (LICPA) scheme. It is shown that an efficient way for achieving high ion beam intensities and fluencies lies in using a short-wavelength laser driver of circular light polarization. In such a case, SLPA clearly dominates over TNSA, and dense and compact ion bunch is generated with high energetic efficiency. The LICPA scheme operating in the photon (radiation) pressure regime can be even more efficient than SLPA. As it is demonstrated by particle-in-cell simulations, the LICPA accelerator with a picosecond, circularly polarized laser driver of intensity ～ 10²¹_?W/cm² can produce sub-picosecond light ion beams of intensity ～ 10²²?W/cm² and fluence?>?1?GJ/cm² with the energetic efficiency of tens of percent. Laser-driven ion beams of such extreme parameters could open up new research areas in high-energy-density science, inertial fusion or nuclear physics.     

Towards a metallic quasi‐d9 system without copper: AgO at high pressure

AgO is a prototypical mixed‐valence compound, with markedly different coordination environment of dumbbell Ag(1+) and low‐spin square‐planar Ag(3+) which render it a narrow band gap semiconductor. The hybrid HSE06 functional reproduces fairly well the band gap of its P 2₁/c form at ambient conditions (ΔE_exp = 1.0–1.1 eV, ΔE_theor = 0.94 eV) and suggest progressive band gap decrease with external pressure with metallization at 50 GPa via band overlap. Dynamic (phonon) instability appears at the onset of metallization leading to a structural phase transition to a more stable but still metallic $$P\stackrel{?}{1}$$ form. The density of electronic states at the Fermi level of the $$P\stackrel{?}{1}$$ polymorph is small and a pseudo‐gap at the Fermi level is preserved.

Illustration of the predicted P2₁/c → $$P\stackrel{?}{1}$$ transformation.     

Electron and magnetic transport in the diluted magnetic semiconductor CdGeAs2<Mn>at high pressures

In CdGeAs₂<Mn>, a metamagnetic phase transition and a negative magnetic resistance induced by high pressure were found and studied.     

Phase transitions of sulfur at high pressure: Influence of temperature and pressure environment

Abstract

Phase transitions of orthorhombic sulfur were investigated above 10 GPa by Raman spectroscopy using red light excitation. Transitions into several phases that have been reported in previous studies using green light excitation, are confirmed. The phase behaviour is observed to depend strongly on the preparation method. In the presence of a pressure transmitting medium (methanol/ethanol, 4:1), a sequence of phases α-S₈ → [intermediate phase (“ip”) + S₆] → [S₆ + high pressure-low temperature phase (“hplt”)] is described and characterized. Without the use of a pressure transmitting medium, the phase sequence α-S₈ → [“ip” + “hplt”] + “hplt” is observed. In addition, contributions of amorphous sulfur are detected around 10 GPa, i.e. at pressures below the transformation of α-S₈ into the above-mentioned phases. Characteristic Raman spectra of the different phases are extracted and documented over a wide pressure range.     

Vibrational properties of Cs4W11O35 and Rb4W11O35 systems: high pressure and polarized Raman spectra

Cs₄ W₁₁O₃₅ (CW) and Rb₄ W₁₁O₃₅ (RW) belong to the class of hexagonal bronzes whose structure originates from the K_xWO₃ superconductor hexatungstate. Charge‐imbalanced tungsten bronzes are dielectric materials with rich polymorphism, ferroelectric properties and second‐harmonic generation. In this work, we report the polarized Raman spectra results for both CW and RW, as well as results of high‐pressure Raman scattering experiments (0.0–11.0 GPa) for the Cs₄ W₁₁O₃₅ system, in which we have observed two structural phase transitions at ∼4 and 7.5 GPa. We discuss these transformations and polarized Raman spectra on the basis of lattice dynamics calculation in the related system KNbW₂O₉. Polarized Raman spectra provide strong indication that the highest wavenumber modes observed in these systems originate from tungsten or oxygen vacancies. The observation of a soft‐like mode indicates that the observed phase transitions exhibit a displacive‐type behavior, thus further indicating that these transformations are likely related to reorientations of the octahedral units. The soft mode nature is discussed as well. PACS: 77.80.Bh; 78.30.Hv; 78.30.‐j. Copyright © 2010 John Wiley & Sons, Ltd.     

High‐pressure Raman spectra of deuterated L‐alanine crystal

Raman spectra of deuterated L ‐alanine have been obtained at high‐pressure conditions. A phase transition at ∼1.5 GPa associated with the splitting of some internal modes and increase of the wavenumber of the external modes was observed. Similarly to the hydrogenated L ‐alanine crystal, this first transition was related to a symmetry change. Moreover, further modifications of the Raman spectra were observed at 4.4 GPa, which may be associated to conformational changes of the molecule. To give further support to such a hypothesis, neutron powder diffraction measurements were performed. Information about the cell parameter at atmospheric pressure gave valuable information about the N D distances, shedding light on the behavior of the torsional vibration of ND₃⁺. Copyright © 2009 John Wiley & Sons, Ltd.     

Employment of a novel ultrasonic method to investigate high pressure phase transitions in oleic acid

In this work, the variation of sound velocity with hydrostatic pressure for oleic acid is evaluated up to 350 MPa. During the measurement, we identified the phase transformation of oleic acid and the presence of the hysteresis of the dependence of sound velocity on pressure. From the performed measurements, it can be seen that the dependence of sound velocity on pressure can be used to investigate phase transformations in natural oils. Ultrasonic waves were excited and detected using piezoelectric LiNbO₃(Y-36 cut) 5 MHz transducers. The phase velocity of the longitudinal ultrasonic waves was measured using a cross-correlation method to evaluate the time of flight.     

Combined field ion microscopy and transmission electron microscopy of heavy ion damage in tungsten

Abstract

A field ion microscopy (FIM) and transmission electron microscopy (TEM) investigation of radiation damage in tungsten after heavy ion bombardment has been carried out. Field ion specimens of tungsten were irradiated with 180–230 keV Xe⁺ ions. The irradiation doses were varied between 4 × 10¹¹ and 4 × 10¹² ions/cm². The irradiated specimens were examined in FIM. Experiments combining both TEM and FIM were performed in order to compare the results obtainable by these two methods. The distribution of defects visible by TEM was inhomogeneous. The influence of the imaging field in FIM on the defects visible in TEM is discussed.     

The hydrogen‐bond effect on the high pressure behavior of hydrazinium monochloride

The first high pressure study of solid hydrazinium monochloride has been performed by in situ Raman spectroscopy and synchrotron X‐ray diffraction (XRD) experiments in diamond anvil cell (DAC) up to 39.5 and 24.6 GPa, respectively. The structure of phase I at room temperature is confirmed to be space group C2/c by the Raman spectral analysis and Rietveld refinement of the XRD pattern. A structural transition from phase I to II is observed at 7.3 GPa. Pressure‐induced position variation of hydrogen atoms in NH₃⁺ unit during the phase transition is attributed to the formation of N―H…Cl hydrogen‐bonds, which play a vital role in the stability and subsequent structural changes of this high energetic material under pressure. This inference is proved from the abnormal pressure shifts and obvious Fermi resonance in NH stretching mode of N₂H₅⁺ ion in the Raman experiment. Finally, a further transition from phase II to III accompanied with a slight internal distortion in the N₂H₅⁺ ions occurs above 19.8 GPa, and phase III persists up to 39.5 GPa. Copyright © 2015 John Wiley & Sons, Ltd.     

High pressure room temperature and high pressure low temperature resistivity studies on As-Te-Se glasses

Abstract

The electrical resistivity measurements have been carried out on bulk As_xTe_100-x-ySe_y (30 ≤ ′ ≤ 50; 10 ≤ y ≤ 25) glasses up to 8 Gpa pressure, and temperature down to 77 K. All the As-Te-Se glasses are found to exhibit a continuous semiconductor to metal transition under pressure. However, glasses with a mean coordination number Z ≥ 2.4 show an initial plateau in resistivity, followed by a continuous decrease. This behaviour is consistent with the earlier observation on the As-Te glasses and is explained in terms of the changes in the local structure of the chalcogenide glasses with the composition.     

High pressure Raman spectra of L‐methionine crystal

Raman spectra of an L ‐methionine (C₅H₁₁NO₂S) crystal were obtained in the spectral region between 50 and 3200 cm⁻¹ for pressures up to 5 GPa. Pronounced changes of the Raman spectra were observed for bands associated to rocking of CO₂⁻; wagging of CO₂⁻; deformations of CO₂⁻, CH₃, and NH₃⁺; and stretching vibrations of SC, CC, CH, CH₂, and CH₃. Upon decompression to ambient pressure the original Raman spectrum prior to compression is recovered. These modifications were associated to a reversible phase transition undergone by the L ‐methionine crystal at about 2.2 GPa, with a hysteresis of ∼0.8 GPa. Pressure coefficients for most of the internal modes of the crystal are given. Copyright © 2008 John Wiley & Sons, Ltd.     

Crystal structure prediction of ReN at high pressure: a new incompressible phase

Based on the swarm-intelligence-based CALYPSO method the NbO, R3m and NiAs phases for ReN are predicted. The R3m phase of ReN at high pressure is firstly found. The structural, mechanical and electronic properties of ReN with the three phases are studied systematically. Moreover, it is also firstly found that pressure stimulated ReN to undergo twice phase transitions, from NbO to R3m phase at 43.3?GPa and from R3m to NiAs phase at 53.6?GPa. The three phases of ReN are verified to be mechanically stable and a promising low-compressible material at ambient conditions. According to the electron density of states and electron localization functions we have found that their structural stability and high hardness is on account of the strong covalent bonding of Re-N and N-N.     

高温高压下钙钛矿晶体结构变化

最近高压单晶X射线衍射实验明确显示正交晶系（Pbnm或Pnma）（钙钛矿）ABO3的高压压缩行为完全由晶体框架结构（framework）中的BO6八面体和AO12多面体的相对压缩性所确定,即对一些钙钛矿晶体,BO6较AO12多面体更易压缩时,压力导致晶体结构向高对称性结构演变;对另外一些钙钛矿,BO6较AO12多面体更不易压缩时,压力导致晶体结构向低对称性结构演变.基于价键匹配关系假设,建立多面体压缩率之间关系：βB/βA=MA/MB,由价键参数和常压晶体结构数据计算参量Mi,可以估计BO6和AO12多面体的相对压缩率,从而正确地预言高压压缩行为.文章最后引入高温高压钙钛矿倾斜相变的一般性规律,即MA/MB＞1时,相变温度和高压关系为dTc/dP＜0,当MA/MB＜1时,dTc/dP＞0。     

高温高压下钙钛矿晶体结构变化

最近高压单晶X射线衍射实验明确显示正交晶系(Pbnm或Pnma) （钙钛矿）ABO3的高压压缩行为完全由晶体框架结构(framework)中的BO6八面体和AO12多面体的相对压缩性所确定,即对一些钙钛矿晶体,BO6较AO12多面体更易压缩时,压力导致晶体结构向高对称性结构演变;对另外一些钙钛矿,BO6较AO12多面体更不易压缩时,压力导致晶体结构向低对称性结构演变.基于价键匹配关系假设,建立多面体压缩率之间关系,由价键参数和常压晶体结构数据计算参量, 可以估计BO6和AO12多面体的相对压缩率,从而正确地预言高压压缩行为.文章最后引入高温高压钙钛矿倾斜相变的一般性规律.