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Using a laser-heated diamond anvil cell, a powdered sample of gallium phosphide was compressed to 17.5 GPa and heated up to 1400 K. The material obtained was characterized at room temperature using synchrotron x-ray diffraction. Experimental results were compared with first-principles calculations. The polymorph observed assumes the simple cubic structure (sc16) initially reported for GaAs at high pressures. Microdiffraction mapping showed variable grain sizes of the synthesized phase, with the largest grains located in the middle of the heated spot. Structural refinements were performed on selected grains. The structure predicted based on first-principles calculations is in close agreement with the experiments. The two Ga–P bonds show similar lengths in sc16-GaP; however, the bond angles differ, resulting in a distorted tetrahedral coordination geometry. [ABSTRACT FROM AUTHOR]

We applied Kawai-type multi-anvil assemblies (MA6-8) for time-of-flight neutron-diffraction experiments to achieve high-pressures and high-temperatures simultaneously. To achieve sufficient signal intensities, the angular access to the sample was enlarged using slits and tapers on the first-stage anvils. Using SiC-binder sintered diamond for the second-stage anvils that transmits neutrons, sufficient signal intensities were achieved at a high-pressure of ∼23.1 GPa. A high-temperature experiment was also conducted at 16.2 GPa and 973 K, validating the use of tungsten carbide for the second-stage anvils. The present study reveals the capability of the MA6-8 cells in neutron-diffraction experiments to attain pressures and temperatures beyond the limits of the conventional MA6-6 cells used in the high-pressure neutron diffractometer PLANET at the MLF, J-PARC. [ABSTRACT FROM AUTHOR]

We have determined the lattice parameters of perdeuterated melamine, C3N6D6, as a function of temperature (4.2-320 K) close to atmospheric pressure and as a function of pressure (0-5 GPa) at room temperature, using time-of-flight neutron powder diffraction methods. Our observations confirm that the ambient-pressure P21/a structure persists throughout this range of P and T. Both the thermal expansion and the compressibility are highly anisotropic; the principal directions of greatest thermal expansion and greatest compressibility are roughly perpendicular to the corrugated sheets of H-bonded melamine molecules that form the main structural motif. Complementary ab initio calculations (van der Waals corrected Density Functional Theory) provide an estimate of how the inter- and intra-molecular geometry may alter as a function pressure in the athermal limit. [ABSTRACT FROM AUTHOR]

The behavior of Ca2AlFeO5 brownmillerite was studied by in situ synchrotron X-ray diffraction and Raman spectroscopy at 300 K with pressures up to 26.5 and 32.1 GPa, respectively. A reversible structural phase transition was observed. The P-V data were fitted by a third-order Birch-Murnaghan equation of state, and the isothermal bulk modulus was obtained as K0 = 181.9(76) GPa with K0′ = 4.4(17). If K0′ was fixed to 4, K0 was obtained as 183.8(20) GPa. Ca2AlFeO5 brownmillerite shows an axial elastic anisotropy since the b-axis is more compressible than a- and c-axis. Combined with previous results, the isothermal bulk modulus and axial compressibility of Ca2AlFeO5 brownmillerite increase with more Al incorporated in the structure. The Raman spectra of Ca2AlFeO5 brownmillerite were analyzed and the pressure coefficients vary from 2.23 to 4.90 cm−1/GPa. The isothermal mode Grüneisen parameters range from 0.83 to 1.77 and the thermal Grüneisen parameter is determined as 1.08(11). [ABSTRACT FROM AUTHOR]

Here, we report experimental results on melting and subsolidus phase relations in the Fe-Fe2P system at 6 GPa and 900-1600°C. The system has two P-bearing compounds: Fe3P and Fe2P. X-ray diffraction patterns of these compounds correspond to schreibersite and barringerite, respectively. The Fe-Fe3P eutectic appears at 1075°C and 16 mol% P. Schreibersite (Fe3P) melts incongruently at 1250°C to produce barringerite (Fe2P) and liquid containing 23 mol% P. Barringerite (Fe2P) melts congruently at 1575°C. Maximum solid solution of P in metallic iron at 6 GPa is 5 mol%. As temperature increases to 1600°C, the P solubility in the metallic iron decreases to 0.5 mol%, whereas the P content in coexisting liquid decreases to 3 mol%. The composition of quenched phases from Fe-P melt coincides with the compositions of equilibrium phases at corresponding temperature. Consequently, the composition of quenched products of Fe-P melts in meteorites can be used for reconstruction of P-T conditions of their crystallization under ambient or low pressures or during shock melting by impact collisions. [ABSTRACT FROM AUTHOR]

In order to constrain the Na2CO3–CaCO3–MgCO3T–Xdiagram at 6 GPa in addition to the binary and pseudo-binary systems we conducted experiments along the Na2CO3–Ca0.5Mg0.5CO3join. At 900–1000°C, melting does not occur and isothermal sections are presented by one-, two- and three-phase regions containing Ca-bearing magnesite, aragonite, Na2CO3(Na2) and Na2(Ca1–0.9Mg0-0.1)3-4(CO3)4-5(Na2Ca3-4), Na4(Ca1–0.6Mg0–0.4)(CO3)3(Na4Ca), Na2(Ca0-0.08Mg1–0.92)(CO3)2(Na2Mg) phases with intermediate compositions. The minimum melting point locates between 1000°C and 1100°C. This point would resemble that of three eutectics: Mgs–Na2Ca3–Na2Mg, Na2Mg–Na2Ca3–Na4Ca or Na2Mg–Na4Ca–Na2, in the compositional interval of [45Na2CO3·55(Ca0.6Mg0.4)CO3]–[60Na2CO3·40Ca0.6Mg0.4CO3]. The liquidus projection has seven primary solidification phase regions for Mgs, Dol, Arg, Na2Ca3, Na4Ca, Na2and Na2Mg. The results suggest that extraction of Na and Ca from silicate to carbonate components has to decrease minimum melting temperature of carbonated mantle rocks to 1000–1100°C at 6 GPa and yields Na-rich dolomitic melt with a Na# (Na2O/(Na2O + CaO + MgO)) ≥ 28 mol%. [ABSTRACT FROM AUTHOR]

Bi-IV is the stable high-pressure, high-temperature phase of bismuth at ∼4 GPa and ∼500 K. It was first identified in 1958, but its structure has remained uncertain. An X-ray powder-diffraction study of Bi-IV reported the structure as monoclinic, but a subsequent reinterpretation of the same data concluded that the structure was C-centred orthorhombic (oC16), with the same atomic arrangement as in Cs-V and Si-VI. To resolve the uncertainty over the structure of Bi-IV, we investigated this phase at 3.2 GPa and 465 K by single-crystal synchrotron X-ray diffraction. All of the observed reflections could be indexed on the orthorhombic oC16 structure proposed by Degtyareva, with a=11.191(5) Å, b=6.622(1) Å and c=6.608(1) Å. The spacegroup was confirmed as Cmce. Refinement of the data resulted in an excellent fit (R=2.8% ), and gave atomic coordinates very similar to those of the oC16 structures in Cs-V and Si-VI. [ABSTRACT FROM PUBLISHER]

In addition to pressure and temperature effects, shear strain has been proposed to play an important role in the initiation and decomposition mechanisms of energetic materials. To study the effect of shear strain in more detail, a shear diamond anvil cell has been developed. In this paper, we present a Raman spectroscopy study of the effects of shear strain on the high-pressure behaviour of nitromethane (NM). Two major effects are observed in our experiments. The first one is a lowering of the pressures at which the different structural modifications of NM occur. The second one is observed at 28 GPa, where the sample decomposes suddenly just after shear application. Examination of the black residue showed that it is composed of carbon, as indicated by the Raman spectrum. [ABSTRACT FROM AUTHOR]

The formation conditions of cubic spinel-structured gallium oxonitride have been investigated in situ under high-pressure/high-temperature conditions using a laser-heated diamond anvil cell. As starting materials, a mixture of the end members w-GaN/β-Ga2O3 in a molar ratio of 3:2 and a gallium oxonitride ceramic derived during pyrolysis from the metallo-organic precursor (Ga(OtBu)2NMe2)2 were used. In the mixture of the end members, spinel-structured gallium oxonitride starts crystallizing at a pressure of 3 GPa and at a temperature of about 1300 °C. The precursor-derived ceramic with predefined bondings reacted completely to the spinel phase, without by-products, at a pressure of 0.7 GPa. For the spinel-structured gallium oxonitride we determined a bulk modulus K of 216(7) GPa using a fixed value of 4 for K'. The spinel-structured gallium oxonitride exhibits a cell volume of 552.9(5) Å3 at ambient pressure. [ABSTRACT FROM AUTHOR]

We report the preliminary results of our recent low-temperature, high-pressure neutron diffraction study of deuterated methane. Contrary to earlier spectroscopic studies of hydrogenous methane, we find no evidence of any structural change between 1 and 5 GPa at 25 K and show that the diffraction patterns can be indexed and refined with the room temperature high-pressure structure of phase A. Our results suggest that either methane shows a remarkably strong isotopic effect or the spectroscopic changes observed are not indicative of structural phase transitions. [ABSTRACT FROM AUTHOR]

The thermodynamic stability of S-substituting Si into a bcc Fe0.80Ni0.05SxSi(0.15-x) random alloy, with x=0.025 n (n=0-- 4), was investigated up to 350 GPa by using an ab initio density functional method based on the full charge density-exact muffin-tin orbital-coherent potential approximation scheme. From the analysis of the calculated Δ H values, we suggest that the FeNiSSi stoichiometry with zero sulphur content always behaves as the most stable system along the whole pressure range of 0-350 GPa. As a general tendency, we found that the alloys with 6.8-8.1 wt.% Si are energetically more stable than those with lower silicon content, thus supporting the dissolution mechanism for the Earth's inner core compositional model. [ABSTRACT FROM AUTHOR]

A program for the automation of the processing of powder diffraction data collected from an area detector is presented in this article. Encapsulation of existing software packages in wrapper programs can allow automation and linking of existing well-proven computer code. This eliminates the need to reinvest resources in developing new codes to meet evolving scientific needs. Here, we demonstrate this principle by automating the use of two programs commonly used in the processing of powder diffraction data from area detectors: fit2d and GSAS. [ABSTRACT FROM AUTHOR]

This short review covers some particular aspects of the production of new materials under high pressures. Despite the fact that there is an extremely wide range of new high-pressure synthesized substances with unique properties, a commercial synthesis has been used up to date only for producing superhard materials - these are real treasures of today's industry. At the same time, as should be underlined here, high-pressure experiments often give scientists material with helpful hints of what new intriguing substances can exist in principle. This is true both for new superhard, semiconducting, magnetic, superconducting, optical materials already synthesized under pressure and a large number of hypothetic new polymers from low-Z elements. [ABSTRACT FROM AUTHOR]

A method of simultaneous X-ray diffraction and electrical resistance measurements of materials in a diamond anvil cell has been developed. The experimental arrangement for the electrical measurements uses a gasket as a part of the electrode scheme. Application of the new methodology is demonstrated on the examples of the study of high-pressure high-temperature behavior of Pr and Fe-Ni alloys. Simultaneously obtained diffraction and resistance data provide the different, from earlier studies, interpretations of the topology of the dhcp-fcc phase transition in the phase diagram of Pr. Namely, the shape of a hysteretic region is mostly defined by kinetics of the dhcp phase growth rather than by thermodynamic driving force at the fcc to dhcp phase transformation. The results of combined X-ray diffraction and resistance measurements of Fe0.8Ni0.2 alloy up to 18 GPa and 425 K are reported along with the complementary resistance measurements of Fe0.9Ni0.1 alloy. [ABSTRACT FROM AUTHOR]

The viscosities of olive oil and its constituent fatty acids were measured using a falling sinker-type high-pressure viscometer. The viscometer consists of a titanium cylindrical sinker with ferrite core and descends concentrically under the influence of gravity through a close-fitting titanium tube. The movement of the sinker was detected by electrical induction through coils surrounding the tube. For the oil and fatty acids, the calculated dynamic viscosity increased according to the model η=ηo exp (β p). The coefficients were readily obtained by linearizing experimental data for sinker fall-times and found to be dependent on the chain length and degree of saturation. [ABSTRACT FROM AUTHOR]

Transmission X-ray diffraction pattern of iron sheared at high pressure show rings whose interplanar spacings correspond to those of ε-iron and their integral multiple, in spite of the fact that it has been kept at atmospheric pressure for ∼3 months from the shearing. This and other related phenomena suggest that the pattern corresponds to the remains of the ε-iron structure in which superlattice formed. The volume of the specimen at atmospheric pressure after elapsing ∼3 months at atmospheric pressure from the shearing was 86% of that before the shearing. [ABSTRACT FROM AUTHOR]

By simultaneously combining the methods of X-ray diffraction for structural phase transitions and EOS measurements, 57 Fe Mössbauer spectroscopy as a site-sensitive probe, and resistivity measurements for studying insulating-metal transitions, we are able to study the effect of extreme pressures and at varying temperature on magnetic and electronic properties of transition metal compounds. Studies are carried out with specially tailored diamond anvils and diamond anvil cells, reaching pressures beyond 100 GPa. From our studies, we can investigate the most basic phenomenon of the quantum effect of magnetism in insulating antiferromagnets, the Mott insulators, such as high to low spin crossovers, quenching of the magnetic moments' orbital term, and the collapse of the Mott-Hubbard state. Examples of these phenomena will be given in cases of ferrous and ferric oxides, ferrous-halides and the rare-earth iron perovskites. [ABSTRACT FROM AUTHOR]

The compound tetrakis(trimethylsilyl)silane Si[Si(CH 3 ) 3 ] 4 (TSi) has been studied at room temperature for pressures up to 21.5(1) GPa, using X-ray powder diffraction with synchrotron radiation. Three different phases are reported in the investigated pressure range. The c.c.p.-type structure is stable up to a pressure of 0.19(1) GPa ( $ \hbox{Fm}\bar{3}\hbox{m} $ , a = 13.5211(1) Å, V = 2471.95(1) Å 3 , Z = 4 at 0.02(1) GPa). It shows a severe orientational disorder of the molecules. At pressures 0.19(1)-0.71(1) GPa a monoclinic phase (HP1) is found with space group P 2 1 / n and Z = 8 ( a = 17.746(1) Å, b = 16.098(1) Å, c = 16.871(1) Å, γ = 111.437(5) and V = 4486.3(8) Å 3 at 0.24(1) GPa). Another monoclinic phase (HP2) exists at pressures 0.52(1)-8.67(5) GPa. This phase has a smaller unit cell than the HP1 phase with Z = 2 ( a = 8.3778(8) Å, b = 9.1050(7) Å, c = 13.3024(8) Å, γ = 111.63(1) and V = 943.22(6) Å 3 at 1.73(2) GPa). The pressure dependencies of the unit-cell volumes are successfully described by Murnaghan or Vinet-type equations of state. The structures at different pressures and temperatures of TSi and related compounds are described as distorted superstructures of the c.c.p. arrangement. The occurrence of different superstructures is rationalized as the result of an optimized packing of ordered molecules of various shapes. [ABSTRACT FROM AUTHOR]

High-pressure apparatus (up to 1 GPa) for viscosity measurements (using the capillary method) of a high-viscous medium has been constructed. High-pressure phases of pure castor oil and methyl alcohol doped castor oil, which had been obtained earlier, were generated and their viscosity measured. Values of viscosity as high as 160 kPas for pure castor oil and 60 kPas for methyl alcohol doped castor oil (about 5 of volume %), at a small shear rate parameter equal to about 0.1 s -1 , were measured and their structural (tixotropic) type viscosity (consistency) were discovered. [ABSTRACT FROM AUTHOR]

In order to examine the pressure effect on anharmonic thermal vibrations of Pt, Extended X-ray Absorption Fine Structure (EXAFS) spectra near Pt K-edge and L 3 -edge were measured in the temperature range from 300 to 800 K under pressures up to 6 GPa, using large volume high-pressure devices and synchrotron radiation. We have investigated the anharmonic interatomic potentials by a cumulant expansion method. The values of EXAFS Debye-Waller factors, σ2 and σ3, become smaller with increase of pressure. The anharmonic effective pair potential V ( u ) = (1/2!) au 2 + (1/3!) bu 3 was evaluated and the potential coefficient a at 0.1 MPa and 6 GPa are 4.8 and 5.0 eV/Å 2 , respectively. The anharmonic potential parameter b decreases with increasing pressure. [ABSTRACT FROM AUTHOR]

We present a new experimental set-up for combined angle dispersive XRD and energy dispersive XAS measurements at high pressure successfully commissioned on the dispersive XAS beamline (ID24) at the ESRF. We illustrate preliminary results on a test experiment performed on ZnCl 2 in the pressure and temperature range up to 6 GPa and 650 K respectively. XAS at Zn K-edge and XRD data of three different phases of ZnCl 2 are shown. [ABSTRACT FROM AUTHOR]