Solid Pressure Medium Research Articles

Pressure effect on the electromotive force of the type R thermocouple

ABSTRACTThe pressure effect on the electromotive force (EMF) of a Pt13Rh–Pt (type R) thermocouple was examined to determine the temperature measurement accuracy of solid pressure medium apparatuses in high-pressure experiments. Single-wire EMFs were measured up to pressure of 13 GPa and temperature of 1173 K with a Kawai-type multi-anvil apparatus for Pt13Rh and Pt based on the single-wire method. The pressure conditions along the wires were evaluated by in situ X-ray diffraction using synchrotron X-ray radiation. The pressure effect of the Seebeck coefficients of Pt13Rh and Pt were determined by the analysis of the single-wire EMFs and pressure–temperature profiles along the wires and was virtually consistent with those determined in previous studies at lower pressures and temperatures. For type R thermocouple, the difference between the nominal and real temperatures was determined to be as large as –75 K at 13 GPa and 873 K.

Casting Octahedra for Reproducible Multi-Anvil Experiments by 3D-Printed Molds

Making consistent and precise octahedral pressure media is crucial for reproducible high-pressure experiments in the multi-anvil press. Here we report a new approach of casting octahedra using 3D-printed molds, and pressure calibrations for octahedra both with and without pre-existing gaskets (“fins”). The 3D-printed molds for casting octahedra from either Ceramacast 584-OF or 646 cement improve the reproducibility of the octahedra and allow for a pre-existing central hole (for the high-pressure cell assembly) in the final cast product. Pressure and temperature calibrations of the octahedra have been performed based on phase transitions in bismuth (Bi) and silica (SiO2), respectively, in order to determine the efficiency and reproducibility of pressure generation and thermal insulation for cast octahedra designed for use with 18/12, 14/8, and 10/5 multi-anvil assemblies. The pressure-generating efficiency of the 14/8 and 10/5 octahedra with pre-existing gaskets, cast from the 584-OF cement, is similar to that of the corresponding COMPRES (Consortium for Materials Properties Research in Earth Sciences) octahedra, and more efficient than pre-cast octahedra made from the same material but lacking pre-existing gaskets. The efficiency of pre-gasketed 18/12 octahedra made of the 646 cement is markedly lower than those of the 584 cement. However, the 18/12 large-volume octahedra, cast (with fins) from the ZrO2-based 646 cement, also provides efficient thermal insulation. Casting octahedral solid pressure media for multi-anvil experiments using 3D-printed “injection” molds is a low-cost and low failure-rate alternative for conducting reproducible experiments at high pressure in the multi-anvil apparatus.

Isostatic compaction behavior of yttria-stabilized tetragonal zirconia polycrystal powder granules

The compaction behavior of a granulated powder of nanocrystalline 3 mol% yttria-stabilized tetragonal ZrO2 polycrystals (3Y-TZP) was investigated by cold isostatic pressing. An elastomer gel was used as the solid pressure medium to form the compacts, in a process referred to as elastomer gel-cold isostatic pressing (E-CIP). The relative density (Dre) of the compact produced by isostatic pressing at a pressure (P) of 1522 MPa is 0.617, which is close to the upper limit of random packing (0.63). A curve fitted to the ln [1/(1–Dre)] vs P1/2 plot shows two linear regions, with a point of intersection at a transition pressure (Pc) of 520 MPa. A coral-like morphology of approximately spherical aggregates remains unchanged in E-CIP compacts formed at below the Pc. Many isolated aggregates are observed in E-CIP compacts formed at above the Pc. Thus, the transition in the fitting curve indicates the destruction of strong bonds between aggregates.

Effect of stress on melting of rhombohedral bismuth

Pressure-induced melting of rhombohedral bismuth (Bi-I) has been investigated in the solid pressure medium of NaCl and the hydrostatic medium of neon at high temperatures by in-situ synchrotron x-ray diffraction. Upon compression from ∼0.7 GPa to 3.2 GPa at (or below) 489 K, Bi-I melts into a liquid between ∼1.2 and 1.6 GPa in the solid pressure medium and then crystallizes into Bi-IV at ∼2.9 GPa. However, at the same temperature of 489 K, Bi-I transforms to a crystalline phase (Bi-II′ or Bi-II) at ∼1.8 GPa under hydrostatic conditions, followed by a transformation to Bi-IV at 2.5 GPa. Our x-ray diffraction results indicate that the melting of Bi-I at (or below) 489 K is due to the stress. There is a stress effect on the structural deformation of Bi-I when the solid pressure medium is used, viz., pressure-dependent c/a for Bi-I in the solid pressure medium is larger or smaller than that under hydrostatic conditions. According to the classical nucleation theory, the stress provides an additional driving force, leading to the reduction of the free energy barrier in the formation of liquid nuclei and thus melting temperature. Additionally, the melting of Bi-I may also be favored by heterogeneous nucleation of the liquid on the boundary between the solid medium and the Bi sample, further contributing to the reduction of the melting temperature.

Superconductivity in the topological insulatorBi2Te3under hydrostatic pressure

We report the resistivity and ac susceptibility measurements of the topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ single crystals at pressures up to 11 GPa. Under highly hydrostatic pressure conditions generated in a multi-anvil high-pressure apparatus, a pressure-induced superconductivity only appears above a critical pressure ${P}_{\mathrm{C}}\ensuremath{\sim}7 \mathrm{GPa}$, coinciding with a structural transition from a rhombohedral to a monoclinic structure. The absence of superconductivity in the rhombohedral phase at pressures below ${P}_{\mathrm{C}}$, which is contrary to previous studies using the high-pressure apparatus with a solid pressure medium, suggests that the occurrence of superconductivity in the rhombohedral phase is sensitive to pressure conditions such as pressure inhomogeneity or uniaxial stress.

High pressure in the synthesis and crystal growth of superconductors and III–N semiconductors

Several high-pressure techniques applied for the synthesis and crystal growth of materials important for the future and present applications are presented. For the synthesis and thermodynamic studies of novel superconductors and III–N wide-gap semiconductors three different high-pressure techniques have been used: (i) the anvil system with solid pressure medium, (ii) the nitrogen/argon gas pressure system, and (iii) the oxygen gas pressure system.

Experimental growth of diopside + merwinite reaction rims: The effect of water on microstructure development

The growth rate and internal organization of bimineralic diopside (CaMgSi2O6)-merwinite (Ca3MgSi2O8) reaction rims produced by a solid-state reaction between monticellite (CaMgSiO4) and wollastonite (CaSiO3) single crystals was determined at 900 °C, 1.2 GPa, and run durations from 5 to 65 h using conventional piston-cylinder equipment. Overall reaction rim thickness ranges from 3.8 to 20.9 μm and increases with the square root of time, indicating that rim growth is diffusion controlled. Symmetrical makeup of the internal microstructure implies that rims grow from the original interface toward both reactants at identical rates, indicating that diffusion of MgO across the rim controls overall growth, with an effective bulk diffusion coefficient of D bulk, MgODi+Mw = 10−16.3 ± 0.2 m2/s. At the initial stages, a “lamellar type” microstructure of alternating palisade-shaped diopside and merwinite grains elongated normal to the reaction front is generated, which gradually transforms into a “segregated multilayer type” microstructure with almost perfectly monomineralic Mw|Di|Mw layers oriented parallel to the reaction fronts at long run durations. This is due to changes in relative component mobilities. Whereas the “lamellar” microstructure develops when MgO is substantially more mobile than the other components, formation of the “segregated multilayer” microstructure requires additional mobility of at least one of the other components, CaO or SiO2. We assume that a significant change in relative component mobilities is caused by continuous entrance of minute amounts of water from the piston-cylinder solid pressure medium through the capsule walls, as revealed by the presence of OH-defects in a reactant after the runs, and supported by water-containing powder experiments that only produce monomineralic Mw|Di|Mw layers. Traces of water have a major influence on relative component mobilities, internal rim organization, and the microstructural development of reaction zones.

Phase diagram of pressure-induced superconductivity in EuFe2As2probed by high-pressure resistivity up to 3.2 GPa

We have constructed a pressure$-$temperature ($P-T$) phase diagram of $P$-induced superconductivity in EuFe$_2$As$_2$ single crystals, via resistivity ($\rho$) measurements up to 3.2 GPa. As hydrostatic pressure is applied, an antiferromagnetic (AF) transition attributed to the FeAs layers at $T_\mathrm{0}$ shifts to lower temperatures, and the corresponding resistive anomaly becomes undetectable for $P$ $\ge$ 2.5 GPa. This suggests that the critical pressure $P_\mathrm{c}$ where $T_\mathrm{0}$ becomes zero is about 2.5 GPa. We have found that the AF order of the Eu$^{2+}$ moments survives up to 3.2 GPa without significant changes in the AF ordering temperature $T_\mathrm{N}$. The superconducting (SC) ground state with a sharp transition to zero resistivity at $T_\mathrm{c}$ $\sim$ 30 K, indicative of bulk superconductivity, emerges in a pressure range from $P_\mathrm{c}$ $\sim$ 2.5 GPa to $\sim$ 3.0 GPa. At pressures close to but outside the SC phase, the $\rho(T)$ curve shows a partial SC transition (i.e., zero resistivity is not attained) followed by a reentrant-like hump at approximately $T_\mathrm{N}$ with decreasing temperature. When nonhydrostatic pressure with a uniaxial-like strain component is applied using a solid pressure medium, the partial superconductivity is continuously observed in a wide pressure range from 1.1 GPa to 3.2 GPa.

Effects of Uniaxial Stress on the Equation of State of Au—A Pitfall in High-Pressure X-ray Diffraction Experiments

The equation of state of gold is widely used as an x-ray pressure standard. The determination of volume by powder x-ray diffraction is, however, severely affected by the presence of uniaxial stress in the sample at high pressures. If a crystal lattice deforms under uniaxial stress, the measured d-spacings deviate from the hydrostatic values, depending on the geometry of the x-ray diffraction experiment. We can analyze the stress state of a cubic crystal with the use of the gamma plot. In the case of gold pressurized with helium, we found that the uniaxial stress differs by experiment, specifically how large the gasket hole deforms under high pressure. This could be the major reason for the discrepancy of the measured lattice parameter of gold. Some general remarks on the solid pressure media are also given.

AlxGa1−xN bulk single crystals

AlxGa1−xN bulk single crystals have been grown by a solution growth technique in a cubic anvil cell with a solid pressure medium. GaN powder pellets as starting materials serve as a nitrogen source for crystallization in a Ga∕Al alloy. The growth process (up to 3days at T=1750°C, p=30kbar) yields crystals up to 0.6×0.4×0.2mm3 in size. X-ray diffraction investigations confirm the growth of the AlxGa1−xN phase. The crystal composition is studied by mass spectrometry, showing aluminum contents as high as x=27%. The near-band-gap photoluminescence spectra in AlxGa1−xN are blueshifted with respect to GaN and indicate Al concentrations in agreement with results from mass spectrometry and from the measured lattice parameter contraction.

Comparative magnetotransport andTc measurementson κ-(BEDT-TTF)2Cu(SCN)2 under pressure

We compare magnetotransport measurements under pressure on the organic superconductorκ-(BEDT-TTF)2Cu(SCN)2 (BEDT- (ethylene-dithio)tetrathiafulvalene) with different pressure media and discover thatthe results are pressure media dependent. This pressure medium dependence isthought to originate from the difference in thermal contraction between the verysoft and highly anisotropic sample and the isotropically contracting, but solidpressure medium, thus resulting in non-hydrostatic pressure on the sample. However,comparison of pressure measurements with different media reveals a pressure mediumindependent correlation between the superconducting transition temperature,Tc, and thesize of the quasi-two-dimensional Fermi surface pocket and thus the quasi-two-dimensional carrier densityin κ-(BEDT-TTF)2Cu(SCN)2. The observed pressure-induced increase in the quasi-two-dimensional carrier density canbe interpreted as a transfer of carriers from quasi-one-dimensional Fermi surface sections,reminiscent of a mechanism in cuprate superconductors, where pressure is known totransfer carriers from the insulating charge reservoir layers into the conducting cupratesheets.

Single-crystal elasticity of MgO at high pressure

The single-crystal elastic properties of MgO were measured by Brillouin scattering in diamond anvil cell to 18.6 GPa. These measurements demonstrate that quasihydrostatic stress conditions can be obtained in solid pressure medium by thermal annealing, and establish the accuracy with which elastic moduli can be measured over this extensive pressure range (\ifmmode\pm\else\textpm\fi{}5% in ${\mathrm{dC}}_{\mathrm{ij}}/dP).$ The acoustic anisotropy of MgO decreases with pressure, with MgO becoming isotropic at \ensuremath{\sim}21.5 GPa. Deviations from noncentral interatomic forces, as measured by the Cauchy relations, increase steadily with pressure.

Pressure-induced phases in the spin-Peierls compoundCuGeO3

The high-pressure behavior of the spin-Peierls compound ${\mathrm{CuGeO}}_{3}$ has been studied at room temperature using high-pressure Raman spectroscopy and optical microscopy in the diamond anvil cell. A number of pressure media, including helium, were used to study the behavior. Three pressure-induced phase transitions were found in the 7--10 GPa region: a pale-green phase (phase II) reported earlier, and two other phases, a blue phase (phase III), and a green phase (phase IV). Phase II is obtained only under strictly hydrostatic conditions (viz., helium, methanol, and methanol/ethanol mixture as pressure media) near 7 GPa. Phases III and IV are obtained near 7 GPa when phase I is pressurized in quasihydrostatic or solid pressure media, viz., argon, KBr, etc. Phase IV reverts to phase III, which can be quenched down to ambient pressure and retained. Using the known crystal chemistry of metasilicates and germanates, the pyroxene structure type arrangements are suggested for phases III and IV.

Effects of a third phase on the mechanical and microstructural evolution of a granulite

To help constrain the rheology of and strain partitioning in composite silicates from lower contintental crust (LCC), opx-hbl-plag granulite samples were shortened coaxially 15–40% in a solid pressure medium (NaCl) apparatus at P c = 1.0 GPa, T = 650–950°C, and strain rates from 10 −5 to 10 −7 s −1. The resultant mechanical behaviour and microstructures are compared with those of Pikwitonei amphibolite (58% hbl, 42% plag) deformed by Wilks and Carter (1990) under similar conditions. The opx-hbl-plag rock is stronger than the hbl-plag rock at all conditions. All samples strain soften beyond 10% strain and stress levels do not reach steady state once softening begins. At low T and high strain rates, relative mineral strength is plag ⪡ opx ⩽ hbl, whereas at higher T and lower strain rates relative mineral strength is opx ⪡ plag < hbl. Opx grains are extensively kinked by glide on (010)[001] at all conditions, plagioclase deforms by translation glide and mechanical twinning that becomes more abundant with higher T, and amphibole deforms by slip on (100)[001]; microcracking in all phases partially accommodates strain under all conditions. Recovery mechanisms are limited even at the highest temperature and lowest strain rates. Tubules along grain boundaries and within grains suggest that a fluid phase, possibly related to amphibole breakdown, was present during experiments. Semibrittle shear zones (SSZs) comprising S-C fabrics defined by elongate grains of all phases develop in all samples; SSZs initiation coincides with the onset of mechanical softening. SSZs initiate along grain boundaries and widen with increasing strain, which accounts for progressive softening with time. Similar S-C fabrics have been duplicated in simple shear tests under indentical conditions which, in turn, are comparable to fabrics in naturally deformed LCC rocks. Increasing the number of co-existing hard phases in natural composite silicates promotes strain localisation by enhancing ductility contrast(s) between constituent phases.

Laser-heated diamond anvil cell experiments at high pressure: Melting curve of nickel up to 700 kbar

Laser-heated experiments in a diamond anvil cell have been performed on high pressure melting of nickel up to 700 kbar. The laser heating system consists of diamond anvil cell, Nd:YAG and argon lasers, spectrograph with diode array, computer with software, CCD camera with monitor and optics. Experiments on melting of tungsten, nickel and platinum at 1 bar outside the diamond anvil cell and melting of nickel below 80 kbar in the cell were carried out to check the system for pressure and temperature measurements. The results show that for solid pressure medium the uncertainties in measurements of pressure at the experimental spot vary between ±5 kbar at 100 kbar and ±25 kbar at 660 kbar. Spectroradiometrically determined temperature is reliable within ±70 K. Melting was detected in situ by visual observation. The melting point of nickel at 660 kbar has been found to be 2557 ±66 K.

Compressions of ta10w alloy kennertium w-2, and beryllium oxide to 4.5 GPa

Abstract The volume compressions of a tantalum alloy, tungsten alloy, and beryllium oxide (BeO) have been derived from the measurements of axial shortenings of cylindrical specimens of these materials to 4.5 GPa at room temperature. These measurements were carried out in a solid pressure medium piston- cylinder apparatus.

Ruby thermometer for cryobaric diamond-anvil cell

The ruby R-line luminescence, commonly used as a manometer in diamond-anvil cell experiments, is shown also to be a useful thermometer over the range 10–100 K. Measurements up to 120 kbar in a solid Ar pressure medium demonstrate that the intensity ratio of the two R lines is thermally activated; in agreement with elementary theory the activation energy is given by the R1–R2 splitting. Based on this dependence, the in-situ temperature of the diamond-anvil cell sample chamber can be determined with ∼10% accuracy over 10–100 K. To apply the ruby thermometer method, no additional effort is needed beyond that already incurred in the standard ruby pressure measurement. The method remains applicable under conditions of moderately nonhydrostatic pressure. The problem of laser heating is discussed.

Measurement of anisotropic stress field in a gasketed diamond-anvil cell

A new technique is proposed to evaluate the axial and lateral stress components, p z and p r , separately within the solid pressure medium of a gasketed diamond cell. The values of p z and p r are obtained from shifts of the R-line of two ruby plate fragments placed in a pressure chamber, one having crystal plane (11 2 0) and the other (0001) parallel to the anvil face.

Electrical Resistances of Manganin and Constantan in Solid Pressure Media

Electrical Resistances of Manganin and Constantan in Solid Pressure Media

Adiabats (∂T/∂P)s and Grüneisen parameter of NaCl up to 50 kilobars and 800°C

The adiabatic pressure derivative of temperature (∂T/∂P)s of sodium chloride has been measured by adiabatic compression up to 50 kbars and 800°C using an end‐loaded piston cylinder apparatus with solid pressure medium. Our measurements at room temperature are in very good agreement with measurements using hydrostatic fluid cells (Boehler et al., 1977). The results can be represented by a power law relationship between (∂T/∂P)s and volume of the form (∂T/∂P)s,P = (∂T/∂P)s,P=0 (V/V0)n. We estimate powers n of 6.3 and 5.3 at room temperature and 800°C, respectively. The Grüneisen parameter γ can be calculated from the thermodynamic equation γ = Ks/T = (∂T/∂P)s, where Ks is the adiabatic bulk modulus; γ is found to be independent of temperature within our pressure and temperature range.