Membrane Diamond Anvil Cell Research Articles

Ag2Mo3O10·2H2O nanorods under high pressure: In situ Raman spectroscopy

This work presents a pressure-dependent behavior of silver trimolybdate dihydrate (Ag2Mo3O10·2H2O) nanorods using in situ Raman scattering. The Ag2Mo3O10·2H2O nanorods were obtained by the hydrothermal method at 140 °C for 6 h. The structural and morphological characterization of the sample was performed by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pressure-dependent Raman scattering studies were performed on Ag2Mo3O10·2H2O nanorods up to 5.0 GPa using a membrane diamond-anvil cell (MDAC). The vibrational spectra under high pressure showed splitting and emergence of new bands above 0.5 GPa and 2.9 GPa. Reversible phase transformations under pressure were observed in silver trimolybdate dihydrate nanorods: Phase I - ambient phase (1 atm − 0.5 GPa) → Phase II (0.8 GPa − 2.9 GPa) → Phase III (above 3.4 GPa).

A symmetric miniature diamond anvil cell for magnetic measurements on dense hydrides in a SQUID magnetometer

ABSTRACTA new miniature diamond anvil cell was specifically designed to detect superconductivity using a SQUID (Superconducting QUantum Interference Device) magnetometer in dense hydrides directly synthesized by the reaction of hydrogen with a chemical element. The cell, made of a CuTi alloy, is fully symmetric with a very low magnetic background allowing the detection of the superconductivity of a sample as small as 3.4 × 104 µm3 without background subtraction. DC measurements or AC measurements in a Magnetic Property Measurement System 3 SQUID magnetometer from Quantum Design could be performed at temperatures as low as 3 K. This high pressure cell is inserted in a modified conventional membrane diamond anvil cell to be driven for hydrogen gas loading and for fine pressure increase before magnetic measurements are performed. To synthetize and structurally characterize the superconducting sample, a 21° optical and 8.6° X-ray acceptance angle allows one to perform laser heating and X-ray diffraction at the same time. A first measurement is shown on the PdH system.

Pressure induced polymerization of fluid ethylene.

The spontaneous polymerization of fluid ethylene under high temperature and pressure conditions has been characterized by using FTIR absorption spectroscopy. The fluid has been isobarically heated at pressures ranging between 0.4 and 1.5 GPa by means of a resistively heated membrane diamond anvil cell. Besides tracing the instability boundary for spontaneous polymerization in the fluid, we have also measured the reaction kinetics at 1.5 GPa and temperatures ranging between 340 and 423 K. From the rate constants the activation energy of the overall reaction could be computed, information that joined to the molecularity of the initiation step provides some insight about the reaction mechanism. The polymers recovered from the different reactions have been characterized by FTIR, Raman, and X-ray diffraction revealing in all the cases a crystalline material of astonishing quality, likely related to the growth of the polymer in the hot fluid monomer.

High-pressure Raman scattering on Fe2(MoO4)3 microcrystals obtained by a hydrothermal method

This study reports on the effect of high hydrostatic pressure on the vibrational spectra of Fe2(MoO4)3 microcrystals using Raman scattering in combination with a membrane diamond-anvil cell. The ferric molybdate was obtained by the conventional hydrothermal method, and the structural and morphological properties of the sample were characterized using additionally X-ray diffraction, scanning electron microscopy, as well as energy dispersive spectroscopy. The X-ray diffraction measurements have shown that the crystals have a monoclinic structure. At pressures higher than 4.8GPa, the disappearance of external modes was observed, suggesting that pressure has induced a breakdown in the translational symmetry of the crystal system. The high-pressure amorphous phase is reversible and attributed to an incomplete crystal-amorphous transformation.

In situx-ray diffraction of fast compressed iron: Analysis of strains and stress under non-hydrostatic pressure

Series of high-pressure x-ray diffraction patterns of iron and its high-pressure polymorphs were collected with 0.1--0.2-s exposure time utilizing a membrane diamond anvil cell (DAC) for compression at various loading and unloading rates to a maximum pressure of 70 GPa. Strain rates of ${10}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at a maximum pressurization rate of 4.1 GPa/s were achieved in non-hydrostatic compression of hcp Fe. Linewidth analysis was used to retrieve strain and uniaxial stress of Fe as a function of pressure upon both compression and decompression. Analysis of the lattice parameters ratio $c/a$ of hcp Fe indicates the presence of complex non-hydrostatic stress states, which developed as a function of strain rate, relaxation time, and various levels of hydrostaticity. Our results emphasize the importance of a controlled pressurization in DACs because the experimental loading rate strongly influences the stress state of the sample, particularly on decompression. Our time-resolved x-ray diffraction of the phase transition from bcc Fe to hcp Fe reveals residual grains of bcc Fe capable of surviving to very high pressures ($>35$ GPa) for a few minutes after the transition.

High-temperature experiments using a resistively heated high-pressure membrane diamond anvil cell

We describe a reliable high performance resistive heating method developed for the membrane diamond anvil cell. This method generates homogenous high temperatures at high pressure in the whole sample for extended operation period. It relies on two mini coil heaters made of Pt-Rh alloy wire mounted around the diamond anvils and gasket, while temperature is monitored by two K-type thermocouples mounted near the sample. The sample, diamonds, and tungsten-carbide seats are thermally insulated from the piston and cylinder keeping the cell temperature below 750 K while the sample temperature is 1200 K. The cell with the heaters is placed in a vacuum oven to prevent oxidation and unnecessary heat loss. This assembly allows complete remote operation, ideally suited for experiments at synchrotron facilities. Capabilities of the setup are demonstrated for in situ Raman and synchrotron x-ray diffraction measurements. We show experimental measurements from isothermal compression at 900 K and 580 K to 100 GPa and 185 GPa, respectively, and quasi-isobaric compression at 95 GPa over 1000 K.

Ambient- and low-temperature synchrotron x-ray diffraction study of BaFe2As2and CaFe2As2at high pressures up to 56 GPa

We report on high-pressure powder synchrotron x-ray diffraction studies on $M$Fe${}_{2}$As${}_{2}$ ($M$$=$Ba, Ca) over a range of temperatures and pressures up to about 56 GPa using a membrane diamond-anvil cell. Our data indicate a phase transition to a collapsed tetragonal phase in both compounds upon compression. The data at 300 K are measured in both pressure-increasing and -decreasing cycles. Our measurements show that at 300 K in the Ba compound, the transition occurs at 27 GPa, which is much higher than the transition pressure of 1.7 GPa in the Ca compound. At low temperature, we could obtain data only in the pressure-increasing cycle, therefore a precise transition pressure is not identified. At a low temperature of 33 K, the transition to the tetragonal phase in the Ba compound starts, upon compression, at about 29 GPa, which is much higher than the transition pressure of 0.3 GPa at 40 K as known in the case of the Ca compound. The much higher transition pressure in the Ba compound may be due to its larger unit-cell volume at ambient pressure. It is important to note that the transition in both compounds occurs when they are compressed to almost the same value of the unit-cell volume and attain similar ${c}_{t}/{a}_{t}$ ratios. We also show that the FeAs${}_{4}$ tetrahedra are much less compressible and more distorted in the collapsed tetragonal phase than their nearly regular shape in the ambient pressure phase. We present a detailed analysis of the pressure dependence of the structures as well as equations of state in these important BaFe${}_{2}$As${}_{2}$ and CaFe${}_{2}$As${}_{2}$ compounds.

Combination of optical and X-ray techniques in the study of amorphous semiconductors under high pressure: an upgrade setup for combined XAS and XRD measurements

X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) are complementary techniques whose combination is a powerful tool of investigation of matter under extreme conditions (high pressure, high temperature). The standard setup at the ODE beamline (Soleil Synchrotron) has been modified in order to allow the performance of simultaneous XAS/XRD measurements on the same sample. These techniques, together with Raman spectroscopy measurements, were applied to the study of pressure-induced phase transitions of amorphous silicon-germanium alloy (a-Si x Ge1−x , with x=0.75) using a membrane diamond anvil cell as the pressure device.

Nanocrystals of ZnO formed by the hot isostatic pressure method

We present here a novel and simple physical method for obtaining ZnO nanocrystals, using the pressure cycle method and the membrane diamond anvil cell (MDAC) up to 13 GPa at 500 K. The recovered nanocrystals in the wurtzitic ZnO phase (w-ZnO) were characterized by the high-resolution Raman scattering and X-ray diffraction. A single crystal of w-ZnO was used in this work. The high-pressure cell was a MDAC specifically designed for high-temperature studies. The Raman spectra of the high-quality ZnO single crystal and nanocrystals were compared, and we observed both a softening and an asymmetric broadening of the Raman peaks, which are in good agreement with the effect of relaxation of the q-vector selection rule due to quantum size confinement effects. The experimental results confirm the existence of ZnO nanocrystals in the w-ZnO phase with an average diameter of 17 nm.

Crystal Structure of Nitromethane up to the Reaction Threshold Pressure

Angle dispersion X-ray diffraction (AXDX) experiments on nitromethane single crystals and powder were performed at room temperature as a function of pressure up to 19.0 and 27.3 GPa, respectively, in a membrane diamond anvil cell (MDAC). The atomic positions were refined at 1.1, 3.2, 7.6, 11.0, and 15.0 GPa using the single-crystal data, while the equation of state (EOS) was extended up to 27.3 GPa, which is close to the nitromethane decomposition threshold pressure at room temperature in static conditions. The crystal structure was found to be orthorhombic, space group P2(1)2(1)2(1), with four molecules per unit cell, up to the highest pressure. In contrast, the molecular geometry undergoes an important change consisting of a gradual blocking of the methyl group libration about the C-N bond axis, starting just above the melting pressure and completed only between 7.6 and 11.0 GPa. Above this pressure, the orientation of the methyl group is quasi-eclipsed with respect to the NO bonds. This conformation allows the buildup of networks of strong intermolecular O...H-C interactions mainly in the bc and ac planes, stabilizing the crystal structure. This structural evolution determines important modifications in the IR and Raman spectra, occurring around 10 GPa. Present measurements of the Raman and IR vibrational spectra as a function of pressure at different temperatures evidence the existence of a kinetic barrier for this internal rearrangement.

The high pressure reactivity of substituted acetylenes: a vibrational study on diphenylacetylene

This article is part of an extended study concerning the reactivity of acetylenic systems at high pressure and aims to the investigation of the high pressure synthesis and stabilization of polyacetylenic chains. The data for diphenylacetylene (DPA) are interpreted by establishing a comparison with the results obtained for acetylene, phenylacetylene, DPA and benzene. The room temperature high-pressure reaction of DPA was studied by means of Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy using a membrane diamond anvil cell (MDAC). The appearance of the sp3 C–H stretching absorption in the Infrared (IR) spectrum at about 9 GPa, indicates the formation of chemical bonds among the aromatic rings belonging to different DPA molecules. For higher pressures, the Raman data indicate the involvement of the internal C≡C moiety in the chemical transformation. Therefore, due to the steric hindrance of the phenyl rings, the pressure threshold for the reactivity of the two molecular fragments appears in this case to be reversed with respect to other molecular systems. The reaction smoothly occurs until the highest investigated pressure (26.6 GPa), and further proceeds on decompression. The recovered sample, deeply red coloured, was characterized by means of FTIR spectroscopy as an amorphous hydrogenated carbon containing locally ordered polymeric or oligomeric structures, where unreacted DPA molecules may be embedded.

Investigation of Mn site configuration in wurtzite and rock-salt Zn1−xMnxO by means of XAS experiments under pressure

In this paper we report on XANES and EXAFS experiments under pressure on the diluted magnetic semiconductor alloy Zn1-x MnxO [1-4]. Zn1-x MnxO powder was prepared from relatively thick films grown by pulsed laser deposition (PLD) on mica monocrystalline substrates. For XAS measurements under pressure at the K-edge of Mn were carried out at the m-XAS LUCIA beam line (SLS), using a membrane diamond anvil cell with partially perforated diamonds anvils. Silicone oil was used as pressure transmitting medium. XAS was measured in the transmission configuration for samples with high Mn content (x=0.25) and in the fluorescence configuration for samples with low Mn content (x=0.05). In the last case, the sample was excited through a partially perforated diamond and the Mn Kα fluorescence was detected in direction perpendicular to the exciting beam, after crossing a Be gasket. EXAFS analysis reveals that the Mn-O bond distance is practically independent on the Mn concentration. On the other side, slight changes are observed in the XANES spectrum when increasing the Mn content, probably related with the increasing proportion of Mn atoms among the 12 second neighbors. In the wurtzite phase, the Mn-O distance is found to be slightly higher and less compressible than the Zn-O distance in pure ZnO. The wurtzite-to-rock-salt transition is observed in both types of samples with very similar features. On the one side, a dramatic change is observed in the XANES spectrum including a drastic decrease of the pre-peak intensity and a complete restructuring of the above edge oscillations. On the other side, the EXAFS analysis shows the expected increase of the Mn-O distance associated to the first neighbor coordination change from tetrahedral to octahedral. A metastable rock-salt phase is retrieved at ambient pressure for samples with 25% Mn Content.

IR Study of the Pressure Induced Solid State DI- and Polymerization in 1,3-butadiene

The pressure induced chemical reaction of butadiene was studied in the crystal phase by means of FTIR spectroscopy using a Membrane Diamond Anvil Cell (DAC). Two different reaction products, vinylcyclohexene (dimerization) and trans-polybutadiene (polymerization), were obtained. The phase diagram of butadiene was investigated and the existence of an orientationally disordered phase, between the liquid and the ordered solid phase, was identified. The analysis of the time evolution of the integrated absorption of the product bands provides information on the reaction mechanisms. Distinct models are necessary to explain the polymer and the dimer formation.

Optical absorption of zinc selenide doped with cobalt (Zn1−xCoxSe) under hydrostatic pressure

The optical absorption of the diluted magnetic semiconductor Zn1−xCOxSe (x = 0.02) has been measured at room temperature under hydrostatic pressure up to 14GPa in a membrane diamond-anvil cell. We found two absorption features: (i) an absorption structure in the energy range 1.6−1.8eV, with a negligible pressure shift (i.e., 0.45 ± 0.05 meV/GPa) which we have identified as the Co2+(3d7) internal transition 4A2(F)→+4T1(P) and (ii) an onset in the energy range 2−2.7eV which redshifts with pressure (−8.1±0.6meV/GPa). We have attributed such absorption edge to charge transfer between the ZnSe valence band and the Co2+(3d7) levels.

Optical Absorption of Zinc Selenide Doped with Cobalt (Zn1-xCoxSe) under Hydrostatic Pressure

Optical absorption of the diluted magnetic semiconductor Zn1—xCoxSe (x = 0.02) has been measured at room temperature under hydrostatic pressure up to 14 GPa in a membrane diamond-anvil cell. We found two absorption features: (i) an absorption structure in the energy range 1.5 to 1.8 eV, with a negligible pressure shift (i.e. (0.45 ± 0.05) meV/GPa) which we have identified as the Co2+(3d7) internal transition 4A2(F) →4T1(P) and (ii) an onset in the energy range 2 to 2.7 eV which redshifts with pressure (dE/dP = (—8.1 ± 0.6) meV/GPa). We have attributed such absorption edge to charge transfer between the ZnSe valence band and the Co2+(3d7) levels. On the assumption that those levels are absolute energy references, a valence band deformation potential of (—0.8 ± 0.07) eV has been derived.

Experimental setup for Fourier transform infrared spectroscopy studies in condensed matter at high pressure and low temperatures

An experimental setup for Fourier transform infrared (FTIR) studies in condensed matter at high pressure and low temperatures is described. We have adapted a close-cycle cryostat (T=20–300 K) to the sample compartment, which is used as a cryo chamber, of a FTIR spectrometer (frequency range 10–15 000 cm−1). A Cassegrain-type beam condenser is assembled to measure infrared absorptions of samples contained in a membrane diamond anvil cell (P up to 100 GPa). The tuning of the pressure and the cell alignment is performed from outside the evacuated instrument. An additional light path allows visual observation and in situ pressure calibration. The advantages of this system, demonstrated by its application to CH4 and Ar–(H2)2 crystals, are high radiation throughput, long time stability, visual observation of the sample, remote measurement and variation of the local pressure, and remote alignment of the cell with the IR beam.

Anharmonic effects in light scattering due to optical phonons in CuGaS2.

The ternary compound CuGaS2 is a direct energy gap semiconductor ~Eg;2.50 eV at 300 K! that crystallizes in the tetragonal chalcopyrite (I 42d) structure and its isoelectronic cubic analog is ZnS. The temperature dependence ~10–300 K! of the Raman active phonons has been studied up to 18 GPa in a membrane diamond anvil cell, using helium gas as a pressure transmitting medium. These measurements allowed us to determine the temperature dependence of the mode Gruneisen parameters and to separate the isobaric temperature dependence of the optical modes into pure-volume and pure-temperature contributions. By this procedure, the cubic and quartic anharmonicities responsible for the pure-temperature contributions to the mode frequencies were determined. The mode Gruneisen parameters of the center-of-zone G5 1 mode ~which corresponds to the edge-of-zone TA in ZnS! is negative throughout the whole temperature range, reaching 21.12 at 77 K. At low temperatures, this provides a possible driving mechanism for the negative values of the thermal expansion coefficient in semiconductors. @S0163-1829~96!07428-0#

High pressure crystal phases of solid CH4 probed by Fourier transform infrared spectroscopy

High pressure infrared spectra of solid CH4 are reported in the range 0.8–30 GPa at room temperature, coupling a Fourier transform infrared spectrometer to a membrane diamond–anvil cell by means of a high efficiency beam condensing optical system. Two crystal phases, A and B, have been investigated. The phase transition is affected by hysteresis and occurs at 9±0.5 GPa during compression and at 7±0.5 GPa during expansion. Due to hysteresis, the transition has been studied as a function of time at higher pressures and found to undergo a first-order kinetics, with rate constant increasing with pressure. Since our experimental apparatus allows us to perform high pressure Raman measurements too, structural properties of both A and B phases have been proposed from the analysis of the infrared and Raman data. Within the framework of the widely used three-site model, the A phase structure is consistent with a D4h unit cell symmetry. On the contrary, the analysis of the ω1 infrared and Raman multiplets in phase B as a function of pressure suggests quite plausibly a single site, well-ordered crystal structure. By means of group-theoretical arguments it is concluded that CH4 molecules occupy sites of Cs symmetry, while the unit cell symmetry must be chosen among D4h, D6h, Th and Oh groups. Qualitative considerations point to D6h as the more favored unit cell symmetry for phase B.

Pressure and temperature dependences of the raman-active phonons in CuGaS 2

The ternary compound, CuGaS 2 is a direct energy gap semiconductor ( E g ~ 2.50 eV at 300 K) that crystallizes in the tetragonal chalcopyrite ( I 4 ̄ 2d ) structure and its isoelectronic cubic analog is ZnS. The temperature dependence (10–300 K) of the Raman active phonons has been studied up to 18 GPa in a membrane diamond anvil cell, using helium gas as the pressure transmitting medium. These measurements allowed us to determine the temperature dependence of the mode Grüneisen parameters and to separate the isobaric temperature dependence of the optical modes into pure-volume and pure-temperature contributions. By this procedure, the cubic and quartic anharmonicities responsible for the pure-temperature contributions to the mode frequencies were determined. The mode Grüneisen parameters of the center-of-the-zone Γ 5 1 mode (which corresponds to the edge-of-the-zone TA in ZnS) is negative throughout the whole temperature range, reaching − 0.64 at 77 K. At low temperatures, this provides a possible driving mechanism for the negative values of the thermal expansion coefficient in semiconductors.

A diamond anvil cell for IR microspectroscopy

A large optical-aperture membrane diamond anvil cell designed for infrared spectroscopy is described. The cell offers definite advantages compared to existing systems. Other possibilities concerning x-ray diffraction analyses with the cells are mentioned.