The formation of a diamond layer on a carbide substrate during diamond interaction with Si,WC and Co

Abstract

A diamond layer was formed on a carbide substrate in an irregular temperature field at high pressures (HP). A gradient scheme of HP cell set-up has been developed, which provides for a simultaneous impregnation of opposite planes of a diamond layer by components that differ in melting temperature. The cell temperature field has been calculated and physico-mechanical properties of the obtained composite material have been studied.     

Argentite-Acanthite Transformation in Silver Sulfide as a Disorder-Order Transition

An alternative model has been proposed for the phase transition from cubic argentite ß-Ag₂S to monoclinic acanthite α-Ag₂S in silver sulfide as a disorder–order transition. It has been shown that, as the temperature decreases below the transition temperature T_trans, S atoms equiprobably occupying the sites of the body centered cubic (bcc) nonmetal sublattice of argentite are concentrated at four sites of the monoclinic nonmetal sublattice, whereas the other sites remain vacant. A disorder-order transition channel including three superstructure vectors of k₉ and k₄ stars has been determined. The distribution function of sulfur atoms in monoclinic acanthite α-Ag₂S has been calculated. It has been shown that displacements of sulfur atoms distort the bcc nonmetal sublattice of argentite, forming a monoclinic lattice, where silver atoms are spaced by quite large distances and occupy their crystallographic positions with a probability of 1. The region of allowed values of the long-range order parameters η₉ and η₄ for the model monoclinic ordered phase α-Ag₂S has been determined.

     

A diamond anvil cell for the study of fluid mixtures at high temperatures

Abstract

A new diamond anvil cell has been developed to study the phase behavior of fluid mixtures at high temperature. Special care has been taken to achieve good temperature stability and small temperature gradients. Preliminar experiments show that the cell performs well.     

A system for doing low temperature-high pressure single crystal X-ray diffraction with a synchrotron source

Abstract

A new diamond anvil cell and a helium flow cryostat have been developed for X-ray diffraction on single crystals at low temperatures and high pressures using white radiation of a synchrotron beam. This novel instrument especially enables continuous change of temperature and pressure of the sample without any adjustment of alignment. Automatic search for diffraction peaks can be performed since less than 30 pm eccentricity can be maintained during the rotation of the cell in the cryostat and the rotation of the cryostat on the goniometer head. The minimum temperature reached is 46 K. Measurements of solid 4He at 11.8 GPa are presented which confirm the stability of the hcp phase on this isobar.     

Equations of state of MgO at high pressure and temperature

Abstract

A synchrotron X-ray diffraction study on MgO has been done at simultaneous high pressure and temperature. The lattice parameter of MgO has been measured up to a static pressure of 6 GPa and a temperature of 1273 K, using a large volume pressure cell and energy-dispersive synchrotron X-ray powder diffraction. The compression was made following six high-temperature isotherms. A Vinet equation of state was used to fit the experimental P-V-T data. The Vinet's model compares very well with the experimental data above the Debye temperature (760 K) and allows the use of MgO as an alternative internal pressure calibrant for experiments at high temperature.     

Synthesis of a new potassium titanate,KTiO2(OH) by hydrothermal oxidation of Ti

Abstract

A new titanium hydroxide KTi₂O(OH) has been synthesized by hydrothermal oxidation of titanium powder in concentrated potassium hydroxide solution. A formation diagram of products synthesized in Ti-KOH-H₂O system at the region of KOH concentration from 0 to 90mol.kg-^?1-H₂O and the temperature from 150 to 350°C has been also constructed.     

Compressibility of a zinc single crystal under confining pressure

Abstract

In the present study, the two compressibility moduli of a zinc single crystal were measured at room temperature up to 18 GPa. The results are compared with those obtained by Bridgman from a different experimental method. This study required a gaseous hydrostatic confining pressure, and then it has been necessary to develop an original diamond anvil cell with a large optical aperture allowing the use of sophisticated video imaging and image analysis techniques. A model is proposed for the zinc volume-pressure relation.     

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.     

Annealing behaviour of arsenic implants in silicon

Abstract

The annealing behaviour of 80 keV room temperature arsenic implants in silicon below the amorphization dose has been studied by comparing the physical profile and the electrical profiles following different isochronal anneals.

It is shown that the electrically active fraction, which is about 0.4 after 30 min annealing at 600°C, increases continuously until 100% electrical activation of the arsenic ions is reached at about 900°C.

The activation energy for the annealing process has been found equal to 0.4 eV. A tentative interpretation of the mechanism involved is given.

From the analysis of the physical profiles obtained after isochronal annealing, an effective diffusion coefficient at 900°C equal to 5 × 10^?16 cm² s^?1 has been calculated.     

Large volume high pressure research using the wiggler port at NSLS

Abstract

A DIA-type cubic-anvil high pressure apparatus (SAM-85) has been interfaced with white x-ray radiation from the superconducting wiggler port of the National Synchrotron Light Source at Brookhaven National Laboratory. Energy-dispersive x-ray diffraction measurements can be obtained for samples with dimensions of the order of 1 mm as a function of pressure and temperature utilizing x-ray energies of up to100 keV.

The sample environment is examined. Pressure is uniform in the sample chamber to within 0.1 GPa, and temperature is constant in the scattering volume to within 5°C.A method is defined for determining deviatoric stress. We find that for a sample containing NaCl and Au, the deviatoric stress increases to about 0.3 GPa as pressure increases to 1.5 GPa and then remains constant, probably reflecting the strength of the sample. Upon heating, the deviatoric stress quickly approaches zero.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’, Daresbury Laboratory 20-21 July 1991     

Synthesis and Structural Characterization of a New Phase of GaAsO 4

A new polymorph of GaAsO 4 has been synthesised at high pressure and temperature (60 kbar and 1273 K). Samples were characterised by powder X-ray diffraction, scanning electron microscopy and EDAX spectroscopy. This material shows an hexagonal symmetry with cell parameters, a =8.1931(4) Å and c =4.3744(2) Å; particles are of hexagonal shape with a narrow size distribution around 2-3 w m and composition close to the Ga:As atomic ratio=1:1. This new high pressure phase of GaAsO 4 represents a new transition path for the ABO 4 compounds.     

Measurements of hall-effect and sheet resistivity as a function of temperature on hot,phosphorous implants in silicon

Abstract

Results of Hall-effect measurements as a function of temperature on a layer formed by hot, phosphorous (P³¹) implant in Si at 400 keV energy in a random direction are presented; the dose used was 10¹⁵ ions cm^?2. The electrical behaviour of the layer as a function of isochronal annealing was examined.

A detailed analysis of the measured quantities n _8eff, the effective surface density of free carriers, and μ_eff, the effective mobility, down to 4.2°K is presented using the integral equations:

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These formulae were solved numerically, the input data viz: the distribution of donor centres and compensating damage centres being assumed from the current literature.

Results from this analysis indicate a rather complicated distribution of current flow in the layer as a function of temperature, indicating that the traditional interpretation of Hall measurements based on a homogeneous distribution model is of questionable validity.     

A low-temperature high-pressure apparatus with a temperature control system

Abstract

A low-temperature high-pressure apparatus was designed using commercial cryogenic equipment. Pressures up to 1 GPa and temperatures down to 40 K can be obtained in a volume of up to 30 cm³. The apparatus is of the piston-cylinder type with a piston diameter of 45 mm, and the pressure can be varied at all temperatures, An adaptive temperature control system keeps the temperature inside the pressure cylinder constant to within ±0.1 K.     

Comparison of the Raman pressure shift and the Raman temperature shift of benzene and diamond with the ruby soale

Abstract

In order to serve as substitute for the pressure ruby scale at high temperature, the breathing mode of bemsens (990 cm^?1) and the first order Raman mode of diamond (1333 cm^?1) have been studied as a function of pressure and temperature in the range of 0–15 GPa and 25–400°C. The diamond and bensene Raman frequency shifts are shoft to be of valuable use as a pressure scale at high temperature. A further advantage of bensene is to remain a suitable pressure transmitting medium up to 350°C and 15 GP.     

The Study on the Arc Plasma Temperature Measurement by Optical Emission Spectroscopy with Fiber Optical Transmission

Abstract

A method for transmitting radiation of the arc plasma with multimode fused quartz fiber onto the spectrograph has been studied. The plot of the Boltzmann function in emission spectral analysis is used for measuring temperature of the arc plasma. The measured temperature of the arc plasma is 5946.6K from least square linear regression of ln[λI/(gA)] and E_i for a number of the emission line intensities of the excited copper atom. Its regression coefficient and measured precision are ?0.97% and 1.7%, respectively. The advantages of the method of the diagnostic temperature for the arc plasma are absolute measurements of the temperature, remote sensing, precision and suitable for mal-environment, such as high temperature, toxic, explosion, strong magnetic or/and electrical fields.

In addition, we have discussed the effect of the spectroscopic constants, such as transition probability, A , the statistical weight of the upper level, g , and the energy of the upper level, E_i , of copper lines on calculating temperature with a plot of the Boltzmann function in detail. The results show that the accurate measurement of the temperature for the arc plasma is obtained only when the spectroscopic constants are selected correctly.     

Performance of different types of detectors in a high-pressure X-ray study of phase transition

Abstract

Phase transitions in praseodymium and lanthanum under pressure have been studied using a synchrotron powder X-ray diffraction technique. A structure refinement of the distorted fcc phase of Pr using diffraction data collected with an imaging plate (IP) detector demonstrate that among some possible structures the rhombohedral structure with space group R3m best reproduces the observed diffraction pattern. The distorted fcc-fcc phase transition in La was observed as a function of the temperature at 23 GPa using a CCD-based detector. A five-minute exposure sufficiently long to measure the intensities of very weak superlattice reflections from the distorted fcc phase, which has been found to transform to the fcc phase at 550 K. The performance of the IP and a CCD-based detector are compared and their future developments discussed.     

Vibrational frequency shifts of fluid nitrogen fundamental and hot band transitions as a function of pressure and temperature

Abstract

Coherent anti-Stokes Raman scattering (CARS) and spontaneous Raman spectroscopy have been used to obtain vibrational spectra of shock-compressed and static high-pressure fluid nitrogen, respectively. Vibrational frequencies were obtained from the CARS data using a semiclassical model for these spectra. Spontaneous Raman vibrational frequencies were determined by fitting data using a Lorentz shape line. A functional form was found for the dependence of the vibrational frequency on pressure and temperature to 40 GPa and 5000 K, respectively. The result is compared to a recent theoretical model.     

EPR and optical spectra of cupric ions doped in powder strontium maleate tetrahydrate and magnesium Bis (hydrogen maleate) hexahydrate

Abstract

EPR spectra of Cu²⁺ ions doped in a strontium maleate tetrahydrate and magnesium bis (hydrogen maleate) hexahydrate have been studied in X-band at room temperature and at liquid nitrogen temperature. Spin-Hamiltonian parameters have been calculated. Molecular orbital coefficients are obtained by correlating optical absorption data with EPR results.     

Surface modifications of crystalline SiO2 and Al2O3 induced by energetic heavy ions

Abstract

Glasses with composition × CoO.(0.25-x) CaO.0.75 B₂O₃ have been prepared over the range 0 ≤ x ≤ 0.25 containing 2 mol% of V₂O₅. Electron paramagnetic Resonance spectra of VO²⁺ of these glasses has been measured at X-band (ν ≈ 9.15 GHz) at room temperature and at liquid nitrogen temperature. Spin Hamiltonian parameters of the VO²⁺ ions have been calculated. It is found that for x ≤ 0.12 the octahedral symmetry of the V⁴⁺ site is improved. A part of these glasses were annealed at 473 K for 24 hours and EPR spectra were recorded and analysed.     

Wavenumber Calibration of CCD Detector Raman Spectrometers Controlled by a Sinus Arm Drive

Abstract

The calibration procedures needed for use of dispersive Raman spectrometers have been reviewed. Like other high‐precision spectrometers incorporating moving gratings, Raman spectrometers are subject to problems with wavenumber scale accuracy. Commercially available Raman spectrometers of types DILOR‐HORIBA LabRam and RENISHAW System 1000 have been examined for wavenumber scale stability, linearity, and reproducibility. For reliable use of the wavenumber data, daily calibration is a necessity. A procedure to examine the linearity of such mechanical drive systems is presented. A new finding was that the examined spectrometers give wavenumber calibration errors that were quite reproducible from day to day at a given temperature in the laboratory but depended markedly on the selected setting of the gratings. Knowledge of this linearity problem is essential for obtaining a reliable calibration. The most correct calibration was obtained by the use of certain “golden” settings of the sinus drive at a constant temperature of the laboratory. In this way, the examined spectrometers could be used with better precision, without daily calibration, provided the temperature of the room was constant or corrected for. A procedure for correction of these errors by the software is suggested.