Effect of pressure on the properties of DH diode lasers in AlxGa1-xAsySb1-y/GaSb system

Abstract

A helium pressure appparatus for diode laser studies up to 1.4 GPa at 77–300 K has been developed. DH lasers with Al_xGa_1-xAs_ySb_1-y active layers (x=0-0.05) lattice-matched to GaSb substrates have been investigated. It has been shown that in lasers with x,y=0 pressure dependences of the threshold current density (J_th) and the average electron lifetime at the threshold (τ) measured at 80 K depend strongly on the quadratic recombination of L^c ₆ electrons, the characteristic coefficient being 1.5×10^?11 cm³s^?1. The pressure-composition equivalence coefficient dx/dP=2.2×10^?10 Pa^?1 has been obtained for the lowest temperatures used.     

Measurements of emission coefficient for continuum radiation from shock-heated krypton plasmas

Using a shock tube, the ξ factor of krypton has been determined at λ = 456.1 nm by observations of the continuum radiation and simultaneous interferometric measurements of the electron number density. For the electron-density range used (1×10¹⁶cm^-3?n_e?4×10¹⁶cm^-3), we obtain an increase in the ξ factor for decreasing electron densities. These results are compared with theoretical and other experimental data.     

Pressure induced metallization of the antiferromagnetic-insulator CoI

Abstract

High pressure electrical measurements were conducted in the antiferromagnetic insulator CoI, using a miniature Diamond Anvil Cell (DAC). The existence of a Mott Transition predicted from high pressure ¹²⁹I Mgssbauer Spectroscopy (MS)¹ has been verified. At about 8 GPa the system becomes metal1ic as evidenced by the temperature behavior of the conductivity. The conductivity at room temperature, however, still increases with increasing pressure, leveling off at 11 GPa. The metallic behavior in the 8 -11 GPa is explained by coexistence of metallic and insulating clusters via a percolating process. Above 11 GPa the material is completely metallic. This mechanism is consistent with the MS findings.     

Nanocrystals of cdte formed by the pressure cycle method

Recently, it has been shown that CdTe has two sucessive phase transitions over a narrow pressure range at ?3.5 GPa. In this work, the pressure cycle method using a Paris-Edinburgh cell up to 6 GPa has been applied to CdTe samples in order to obtain recovered CdTe nanocrystals which were characterized by high resolution transmission electron microscopy (HRTEM), electron diffraction and Raman scattering. Such retrieved nanocrystals are nearly spherical, with diameters ranging from 10 to 30 nm, and their structure is zinc-blende (ZB). Their Raman spectra is consistent with the CdTe phonon dispersion curves but reveal a phonon confinement effect.     

A study on the formation and stability of quasicrystal in Al4Mn and Al6Cr

Abstract

The condition of the formation of quasicrystal in Al₄Mn and Al₆Cr under high static pressure has been investigated for the first time. I-phase and T-phase have been observed in electron diffraction experiment. The structures of Al₄Mn quenched at about 100 K/s are different under various pressure from 0.95GPa to 4.45GPa. The phase transition from I- and T-phase to crystal phase has also been investigated.     

Measurement of the compressibility of a deuterium plasma at a pressure of 1800 GPa

The thermodynamic properties of a highly compressed deuterium plasma have been measured using an explosive spherical experimental chamber. The experiment has been performed with an X-ray diffraction complex consisting of three betatrons and a multichannel optoelectronic system of the detection of X-ray images of the process of the explosive spherical compression of deuterium. The density of the shock-compressed deuterium plasma ρ = (4.3 ± 0.7) g/cm³ at the pressure P = 1830 GPa has been detected at the initial pressure of gaseous deuterium P ₀ = 267 atm and the temperature T ₀ = 10.5°C. Under such conditions, the plasma is strongly nonideal (Γ ～ 450) with the degenerate (nλ _e ³ ～ 280) electron component and with an electron density of about 2.8 × 10²³ cm^?3.     

Measurement of quasi-isentropic compressibility of helium and deuterium at pressures of 1500–2000 GPa

The quasi-isentropic compressibility of helium and deuterium plasmas at pressures of up to 1500?C2000 GPa has been measured using devices with spherical geometry and an X-ray diagnostic complex comprising three betatrons and a multichannel imaging system with electro-optic gamma detectors. A deuterium density of 4.5 g/cm³ and a helium density of 3.8 g/cm³ have been obtained at pressures of 2210 and 1580 GPa, respectively. The internal energy of a deuterium plasma at the indicated pressure is about 1 MJ/cm³, which is about 100 times greater than the specific energy of condensed chemical explosives. Analysis of the obtained data shows that the degree of helium ionization under the achieved plasma compression parameters is about 0.9.     

Solidification of selenium melt under pressure up to 6.5 GPa

Abstract

High purity selenium samples were melted under high pressure (≤6.4 GPa) and quenched at various rates ranging from 2 K s^?1 to 500 K s^?1 and the recovered material was examined by X-ray diffraction and electron microscopy. In the entire range of pressure and cooling rate, the melt was found to solidify into a polycrystalline aggregate of the trigonal phase of selenium. The samples obtained by slow cooling of the melt at 6.4 GPa contain, in addition to crystalline phase, regions which appear to be amorphous.     

High pressure study of the 2D polymeric phase of C60 by means of raman spectroscopy

Abstract

The effect of high hydrostatic pressure, up to 12GPa, on the intramolecular phonon frequencies and the material stability of the two-dimensional tetragonal Cm polymer has been studied by means of Raman spectroscopy in the spectral range of the radial intramolecular modes (200-800cm^?1). A number of new Raman modes appear in the spectrum for pressures ～ 1.4 and ～ 5.0 GPa. The pressure coefficients for the majority of the phonon modes exhibit changes to lower values at P=4.0 GPa, which may be related to a structural modification of the 2D polymer to a more isotropic phase. The peculiarities observed in the Raman spectra are reversible and the material is stable in the pressure region investigated.     

High-pressure Mössbauer spectroscopy with nuclear forward scattering of synchrotron radiation

Abstract

Using a diamond anvil cell, high-pressure ⁵⁷Fe Mössbauer spectroscopy has been performed with the nuclear forward scattering of synchrotron radiation. A pressure-induced magnetic hyperfine interaction at ⁵⁷Fe in SrFeO_{2, 97} has been detected at 44 GPa and 300 K for a first time by a quantum-beat modulation of the decay rate after collective nuclear excitation by the synchrotron pulse. The basic concept and method used to detect nuclear forward scattering with synchrotron radiation are discussed.     

Electrical conductivity and thermal EMF of CsI at high pressures

Abstract

The pressure dependence of thermal EMF and the resistivity-temperature dependence of CsI has been measured at pressures 20-50 GPa. In CsI non-monotonous change of resistivity, thermal EMF and activation energy of charge carriers has been observed at pressures above 40 GPa. The sign of thermal EMF corresponds to the electron conductivity. At pressures below 47 GPa the resistivity-temperature dependence is of the type characteristic of non-degenerate semiconductors, at pressure above 49 GPa it is characteristic of degenerate semiconductors (or metals). The observed properties are connected probably with the continuous distortion of B2 to an hcp-like phase.     

Shock metamorphism of the graphite quasimonocrystal

Abstract

Micro structure examination of graphite quasimonocrystal recovered after dynamic loading to pressure of 35-45 GPa was carried out. Only a small amount of cubic diamond and recrystalized graphite was detected. Most of the graphite (～80 vol.%) remained in initial high orientation, but transformed to fine, grained phase with crystalite size 0.1-1 microns. Relaxation time of the transformation (～ 10 ns) and the degree of the transformation (～ 70-80 vol.%) were determined by means of measurements of the electrical resistivity during loading up to 26 GPa and following computer simulation of the results. We proposed that two simultaneous processes take place at pressures higher than 20 GPa: i) relatively slow diffusive graphite to diamond transformation localized in the zones with defect structure: ii) highly oriented graphite transforms to a diamond like phase with density of about 3.2 g/cm³ at zero pressure. This, transformation has fast, martensitic kinetics and is reversible.     

High-spin-low-spin transition in magnesiowüstite (Mg<Subscript>0.75</Subscript>,Fe<Subscript>0.25</Subscript>)O at high pressures under hydrostatic conditions

The spin states of Fe²⁺ ions in (Mg_0.75,Fe_0.25)O magnesiowüstite crystals at hydrostatic pressures up to 90 GPa created in a diamond-anvil cell with helium as a pressure-transmitting medium have been investi-gated by transmission and synchrotron Mössbauer spectroscopy at room temperature. An electron transition from the high-spin (HS) state to the low-spin (LS) state (HS-LS crossover) has been observed in the pressure range of 55–70 GPa. The true HS-LS transition occurs in a narrow pressure range and the extension of the electron transition to ～15 GPa is attributed to the effect of the nearest environment and to thermal fluctuations between the high-spin and low-spin states at finite temperatures. It has been found that the lowest pressure at which the electron HS-LS transition can occur in the Mg_{1 ? x} Fe _x system is 50–55 GPa.     

High pressure X-ray diffraction study of copper hydride at room temperature

Abstract

High pressure X-ray studies on CuH up to 23 GPa have been performed at room temperature using a gasketed diamond anvil cell. The experimental data on the molar volume of CuH as a function of pressure have been fitted to Murnaghan's equation of state giving a bulk modulus: B₀ = 72.5±2 GPa and B₀ = 2.7 ± 0.3. By comparison with the equation of state for pure copper the effective additive volume of hydrogen has been evaluated as a function of pressure. It decreases from 3.2 cm³/mol H, at ambient pressure reaching a flattening value of 1.7cm³hol H at about 60 GPa. This suggests a continuous transition of CuH from ionic or covalent character at normal pressure to metallic hydride behavior at high pressure     

High pressure Raman studies on solid iodine

Abstract

Raman spectra of solid iodine were measured up to 27 GPa. Additional bands, whch appear above 10 GPa, are discussed with respect to a quasi one dimensional molecular phase existing at intermediate pressures and may indicate a more subtle way of molecular dissociation than previously suggested. Higher order spectra due to two-and three phonon processes involving internal and external modes were observed up to 10 GPa.     

Ab initio study of the structural,electronic, elastic and thermal conductivity properties of SrClF with pressure effects

Abstract

SrClF is an important optical crystal and can be used as pressure gauge in diamond anvil cell at high pressure. In this work, we performed a systematic study on the structural, electronic and elastic properties of SrClF under pressure, as well as its thermal conductivity, by first-principles calculation. Different exchange-correlation functionals were tested and PBESOL was finally chosen to study these properties of SrClF. Studies reveal that SrClF has a bulk modulus of about 56.2 GPa (by fitting equation of states) or 54.3 GPa (derived from elastic constants), which agree well with the experimental result. SrClF is mechanically and dynamically stable up to 50 GPa. Its elastic constants increase with the applied pressure, but its mechanical anisotropy deteriorates as the pressure increases. Investigation of its electronic properties reveals that SrClF is a direct band-gap insulator with a gap value of 5.73 eV at 0 GPa, which decreases with the increasing pressure and the reason is found by analysing the partial density of states. Based on the calculated phonon dispersion curves, thermal conductivity of SrClF is predicated. At ambient conditions, the predicted thermal conductivity is about 3.74 Wm^?1 K^?1, while that obtained using the simplified Slack model give a slightly larger value of 4.62 Wm^?1 K^?1.     

The influence of pressure on spontaneous magnetization of Fe60Mn20B20 amorphous alloy at temperature range 77.4–300 K

Abstract

Amorphous, ferromagnetic, invar like, Fe₆₀ Mn₂₀ B₂₀ alloy has been investigated. Two kinds of experiments were carried out for this alloy. The first, using high pressure technique, revealed the influence of pressure on B(H) dependencies within the wide range of temperature under pressure of 0.5 GPa. From the magnetization curves obtained during these experiments the decrease of spontaneous magnetization caused by applied pressure 0.5 GPa at temperature -180°C has been calculated at the rate about 7 10^?11T/Pa.

In the second kind of experiments the measurements of volume magnetostriction up to 720 kA/m magnetic field intensity have been done. Volume magnetostriction coefficient at temperature 77.4 K has been determined to be about 2 10^?11 [A/m]^?1.     

A Spectrophotometric Method for the Determination of Buclizine Hydrochloride Using the Charge-Transfer Spectrum of Buclizine-Iodine Complex

Abstract

A simple and sensitive spectrophotometric method is described for the determination of buclizine hydrochloride in bulk and tablets form. The method is based on the formation of charge-transfer complex between buclizine, as n-donor, and iodine, as Δ acceptor, which measured spectrophotometrically at 295 and 355 nm. A Job's plot indicated a 1:1 complex between the drug and iodine and Beer's law was obeyed in a concentration range of 4–30 μg ml^?1. A more detailed investigation of the complex was made with respect to its association constant and the free energy change. The method is simple and sensitive and has been applied successfully to the analysis of laboratory-made tablets without any interference from the tablet excipients. To validate the method, the results obtained were compared statistically with a newly developed uv-derivative spectrophotometric method. The charge-transfer method was favored due to its higher sensitivity, cheap coast and available equipments.     

基于铰链式六面顶压机的二级6-8型大腔体静高压装置

报道了一种新型二级6-8型大腔体静高压装置.该装置是以国产DS6×800T铰链式六面顶压机为构架,在其六面体压腔中直接放入二级6-8模(球分割)增压装置以产生10GPa以上的压力,还实验了不同规格的预密封边和不同密度的叶蜡石对压力产生效率的影响,在室温下用BiⅠ-Ⅱ(2.55GPa),Ⅲ-Ⅴ(7.7GPa)和SnⅠ-Ⅱ(9.4GPa)在高压下的相变对14／8(8面体传压介质边长／8面体压腔边长)规格压腔进行了压力标定.实验结果表明,该系统可以在加载压力(油压)约为3×10⁶N(～42 关键词： 铰链式六面顶压机 6-8型球分割大腔体静高压装置 压力标定     

Quasi-isentropic compression of liquid argon up to 500 GPa

The compressibility of liquid argon up to pressures ∼500 GPa has been investigated experimentally. The argon was compressed by a cylindrical shell accelerated by the detonation products of an explosive. The density was recorded by the gamma-graphic method and the pressure was determined from the gas-dynamic calculations. Comparing the experimental and computational results showed that the compression process studied is isentropic to a quite high degree. The compression of liquid argon up to a density of 7.3 g/cm³ did not show any clear anomalies associated with a structural transition or metallization. Zh. éksp. Teor. Fiz. 111, 2099–2105 (June 1997)