Melting and thermal expansion of iron in uniformly laser-heated diamond anvil cells

Abstract

A technique is described to laser heat samples uniformly under hydrostatic pressure conditions to over 2500 K and 400 kbar with very high accuracy in P and T. I re-measured the melting curve of iron by this technique and obtained excellent agreement with my earlier work using resistive wire heating (Boehler 1986). P-V-T measurements on γ-iron to 200 kbar and 2000 K using synchrotron radiation leads to a strong decrease of the thermal expansion coefficient with pressure, (?lnα/?lnV)_T = 6.5. The zero pressure bulk modulus K₀ decreases with temperature by 0.33 kbar deg^?1. This Yields densities of iron at conditions in the Earth's core which are consistent with shock compression measurements. The potiential of studying mineralogical phase transitions by this method is described.     

High Pressure Instrumentation: Low and Negative Pressures

Much work on semiconductors, soft solids and biological materials does not require the megabar capability of the diamond anvil cell; a few accurate kbar being all that may be required. Work in this range poses its own challenges, to make the experiments routine, safe and reliable, and well-calibrated. We contrast diamond anvil cells working at what for them is very low pressure, with traditional bombs working at what for them is dangerously high pressure. We describe our preferred solution, a single-diamond cell, and demonstrate its use with Raman data from ethanol under low pressure. Negative hydrostatic pressure cannot be obtained by traditional methods. However, we present data showing the Raman spectrum of ethanol apparently at the negative pressure of m 3 kbar.     

Pressure stability of insulin: A fourier transform infrared spectroscopy study

High hydrostatic pressure can induce partially unfolded protein conformations that are highly aggregation prone under conditions that normally favour the native state. We investigated the pressure stability of insulin at pH 2 with Fourier transform infrared spectroscopy. We do not observe any cooperative change up to 13 kbar. All spectral changes in the amide I area are fully reversible and are assumed to arise from the elastic effect of pressure, which causes no conformational changes. Moreover, insulin has no higher temperature-induced aggregation tendency when pressure pre-treated.     

Raman study of rutile (TiO2) at high pressures

The Raman spectra and polymorphism of rutile have been investigated under hydrostatic pressures up to 90 kbar at room temperature. A transition previously observed in rutile at 30 kbar in a Drickamer-type cell under nonhydrostatic conditions was observed to begin at approximately 70 kbar in a 4:1 mixture of methanol and ethanol. The small amount (10–20%) of the high-pressure phase synthesized from rutile, however, did not increase even though the sample was left under pressure for a period of 1 month at ambient temperature. On the basis of factor group analysis, in situ powder x-ray diffraction data, and comparison of the Raman spectrum of the high-pressure modification with that of TiO₂-II (α-PbO₂-type structure synthesized from anatase powder at 40 kbar and 400°C), it is evident that a high pressures rutile transforms irreversibly to TiO₂-II.     

DLTS investigation of GaP under hydrostatic pressure

Abstract

Deep Level Transient Spectroscopy (DLTS) was applied to nitrogen related deep electron trap 0.4 eV in green emitting diodes of GaP under hydrostatic pressure. The pressure coefficient of the level energy is determinated as equal -31 meV/kbar with respect to the valence band edge.     

The SrB4O7:Sm2+ optical sensor and the pressure homogeneization through thermal cycles in diamond anvil cells

Abstract

Preliminary results, up to 550 kbar, on a thermal-cycling relaxation process of the 4.Methanol-1.Ethanol pressure-transmitting medium, are presented. The homogeneization is monitored by linewidth measurements of the ⁵D₀-⁷F₀ emission line of SrB₄O₇:Sm²⁺, recently proposed as an “almost ideal” high pressure calibrant. Above 100 kbar at 20°C, the line broadens linearly with increaisng pressure. Upon heating, at a fixed pressure, the linewidth is reduced to a minimum (“hydrostatic”) value provided a sufficient temperature is reached and this narrowing is irreversible upon cooling. For T=300°C this relaxation is observed for P (250 kbar, incomplete at 340 kbar and not observed at 550 kbar.     

High-pressure spectroscopic studies of free and self-trapped excitons in alkali halides at low temperatures

Abstract

A brief survey of our studies of free and self-trapped excitons (FE and STE) in alkali halide crystals under hydrostatic pressure up to 12.5 kbar at 4.2–140 K is presented. Main attention is paid to the following effects observed: (1) the strong coupling of three energy levels of FE in CsI revealing itself as an exciton analog of pressure-scanned Fermi resonance; (2) emergence of a new emission band of STE in CsI under pressure; (3) a large pressure shift of the thermal quenching curve for STE emission in NaCl.     

Hydrostatic pressure investigations of resonant tunnelling through X-minimum-related states in a single barrier GaAs/AlAs/GaAs heterostructure

Abstract

We have investigated the resonant tunnelling of electrons through X-valley related states in a single AlAs barrier with Si donor & doping. Under high hydrostatic pressure all the peaks observed in the differential conductance-voltage (σ-V) characteristics shift with a pressure rate of -lSmeV/kbar, which is expected for X-minima related electronic states.     

Resonant Raman scattering in polyacetylene under hydrostatic pressure

The results of resonant Raman scattering experiments on trans-poly-acetylene under hydrostatic pressure are reported. The measurements were performed in a diamond anvil cell. The spectra could be measured up to 44 kbar. The pressure dependence of the 1295 cm^-1 line was measured in a sapphire cell up to 17 kbar. The results show that the changes in the phonon frequencies are very small. By comparing the pressure dependence of the Raman bands with their dependence on the photon energy of the exciting laser line it is possible to determine the pressure variation of the electronic energy gap. The results are consistent with previous measurements of the absorption spectrum under hydrostatic pressure which were carried out up to 13.5 kbar. The gap is found to decrease rapidly with pressure but the decrease tends to saturate at high pressures. The results are consistent with a model in which chain-chain interaction plays a dominant role.     

A Theory of Non-Linear Elasticity Compatible With the Murnaghan Equation of State

We present an equation of state for a cubic non-linear elastic material in a general state of finite strain. For hydrostatic pressure, the predictions closely follow Murnaghan's well-known equation of state. At 170 kbar, our model differs from Murnaghan's equation by only 1.3%, which contrasts with the currently accepted non-linear elasticity theory that differs by 10% at this pressure. The theory is based on expressing the variation of the elastic constants as a linear function of stress rather than strain. We define a different set of third-order elastic constants, which involve a derivative with respect to stress, and relate these to the conventional third-order elastic constants. We apply the model to GaAs under hydrostatic pressure and we compare the predictions of the conventional non-linear theory with those of the model we present.     

用高压显微光谱系统研究(Zn0.85Cd0.15)S:Cu,Al磷光体在流体静压力下施主-受主对的发光

用金刚石对顶砧高压显微光谱系统在室温和1bar—66kbar的流体静压力范围内研究了(Zn_0.85Cd_0.15)S:Cu,Al磷光体的发光峰位置和相对发光强度随压力而变化的规律。随着压力的增加,发射峰值波长迅速移向短波方向,而发射峰值对应的光子能量随压力增加的速率为4.7meV/kbar(38cm^-1/kbar)。这个值比该材料的吸收边随压力增加的速率要小。随着压力的增加,该磷光体的发光峰值相对强度急骤下降,当压力从常压升到66kbar时,发光峰值相对强度下降到原值的6％。这些结果可以用Al³⁺-Cu⁺的施主-受主对模型来解释。本文还估计施主(Al³⁺)和受主(Cu⁺)的激活能之和随压力增加的速率为3.7meV/kbar(30cm^-1/kbar)。 关键词：     

Neutron Diffraction Study of the p - T Phase Diagram for Erbium

Electrical resistivity measurements performed on a single crystal of erbium as a function of temperature and hydrostatic pressure have provided a preliminary p - T phase diagram. The results have been interpreted in terms of a model for the magnetic structures of Er deduced from neutron diffraction studies at ambient pressure. This model predicted the existence of a magnetic structure with a wave vector of Q =2/7 c * at 4.2 K, when the applied pressure is larger than 3 kbar. This paper reports a neutron diffraction study of erbium made in the temperature range of 4 to 100 K, at pressures between 0.5 and 6 kbar. We have observed the predicted suppression of the low temperature conical ferromagnetic phase and the emergence of a new phase with Q =8/33 c *. The neutron diffraction measurements has enabled us to identify the various phases that develop from the cycloidal phases previously observed at atmospheric pressure.     

A new hydrostatic medium for diamond anvil cells to 300 kbar pressure

We have shown that the rare gas xenon provides a hydrostatic medium for gasketed samples in a diamond anvil cell to pressures of 300 kbar. Previously, hydrostatic conditions were limited to ～100 kbar in a methanol-ethanol mixture. Three spectroscopic tests were used to determine that pressure gradients were small in the solidified gas. Since xenon has a convenient melting temperature, easy cell loading is possible. The small volume in the gasket requires only a few cm³ of gas. By analogy the other rare gases may be expected to show similar hydrostatic properties. Helium, for example, would be useful for X-ray studies.     

EPR of 3d 5 and 3d 8 Ions in Crystals With Perchlorate Structure at High Pressure

EPR spectra for ions Ni 2+ (3d 5 ) and Mn 2+ (3d 5 ) substituting Zn 2+ in crystals Zn(BF 4 ) 2 ·6H 2 O are studied within a wide range under hydrostatic pressure in X and Q bands. It is shown that the pressure changes to a considerable extent the spectrum parameters of ion Mn 2+ , reducing axial parameter b_{2}^{0} and increasing cubic one b_{4}^{0} at 9 kbar pressure, there is no temperature dependency of parameter b_{2}^{0} . Hydrostatic pressure changes linearly the initial splitting of ion Ni 2+ and results to a change in D(b_{2}^{0}) sign, which means the spin levels inversion at 3.5 kbar.     

X‐ray reflectivity measurements of liquid/solid interfaces under high hydrostatic pressure conditions

A high‐pressure cell for in situ X‐ray reflectivity measurements of liquid/solid interfaces at hydrostatic pressures up to 500 MPa (5 kbar), a pressure regime that is particularly important for the study of protein unfolding, is presented. The original set‐up of this hydrostatic high‐pressure cell is discussed and its unique properties are demonstrated by the investigation of pressure‐induced adsorption of the protein lysozyme onto hydrophobic silicon wafers. The presented results emphasize the enormous potential of X‐ray reflectivity studies under high hydrostatic pressure conditions for the in situ investigation of adsorption phenomena in biological systems.     

High pressure cell for neutron diffraction investigations

Abstract

The design of a titanium-zirconium clamped cylinder-piston type pressure cell for neutron diffraction investigations under hydrostatic pressure up to 10 kbars without supports is described. It is the first time that Freon-11 has been used as a hydrostatic pressure transmitting medium. The following results carried out at the room temperature are presented: the discovery of the transition from I to 111 phase in a LiKSO₄ single crystal and the results of the investigation on the influence of pressure upon the structure of the YBaCuO HTSC obtained by means of the powder diffraction method.     

Optical Spectroscopic Study of Al 2 O 3 : Ti 3+ Under Hydrostatic Pressure

This work investigates the effect of hydrostatic pressure on the excitation, emission and lifetime of Ti 3+ - doped Al 2 O 3 in the 0-110 kbar range. The application of pressure induces band shifts that are correlated with the corresponding local structural changes undergone by the TiO 6 complex. The increase of the Stokes-shift and the reduction of the Jahn-Teller (JT) splittings under pressure are analysed in terms of a simple model based on linear electron-phonon couplings to the a_{1_{\rm g}} and the JT e g vibrational modes.     

Hydrogen vibrations in γ-TiH and γ-ZrH under high pressure

Abstract

The effect of high hydrostatic pressure on the vibrational spectra of monohydrides γ-TiH and γ-ZrH was studied by inelastic neutron scattering, the maximum experimental pressure being, respectively, P=15 and 17·5 kbar. There was observed a uniform linear pressure-induced energy shift of each spectrum compared to that at ambient pressure with proportionality factors of 1·02 for y-TiH and 1·03 for γ-ZrH. The observed linear shift of the one-phonon hydrogen modes and the bound multiphonons (biphonons and triphonons) is indicative of a pressure-induced increase of the anharmonicity parameters in the model Hamiltonian representing the strength of two-phonon and three-phonon interactions.     

Compression behavior of NiO in a diamond cell

Abstract

The compressibility of synthetic polycrystalline NiO was studied in a diamond anvil cell at room temperature utilizing two different X-ray sources. A standard film with a conventional X-ray source and the energy dispersive X-ray diffraction (EDXRD) method with synchrotron radiation were used for data acquisition. In the film method, the sample was compressed in a 4:1 methanol to ethanol solution up to 7 GPa with ruby fluorescence as a pressure calibrant. In the energy dispersive method, NiO powder was mixed with gold and compressed in two different conditions: gasketed and ungasketed up to 30 GPa. In the gasketed run, water was used as the pressure transmitting medium while gold was used as pressure calibrant in both runs.

Hydrostatic compression of NiO in both diffraction methods yields a bulk modulus (K _o) of 187 ± 7 GPa assuming K′ = 4. The compression of gasketed NiO of the synchrotron experiment, however, showed an obvious break at pressure exceeding 4 GPa due to the loss of hydrostaticity. NiO in a nonhydrostatic condition behaves with less compressibility than the hydrostatic results with a nominal K _o of 238 ± 10 GPa. The lower compressibility of NiO in synchrotron runs is attributed to the uniaxial loading effect which was more easily detected by the EDXRD geometry. The discrepancy in the bulk modulus can be attributed to the contrast in the shear strength between the sample and pressure medium and the Poisson effect of the sample under uniaxial loading.     

1H NMR study of [N(CH3)4]2ZnCI4 at high pressures and low temperatures

Wide-line proton NMR studies on polycrystalline tetramethylammonium tetrachlorozincate have been carried out at high hydrostatic pressures up to 15 kbar in the temperature range 77-300 K and at ambient pressure down to 4.2 K. A second-moment transition is observed to occur starting around 161 K, the temperature for the V-VI phase transition. This transition temperature is seen to have a negative pressure coefficient up to 2 kbar, beyond which it changes sign. At 77 K the second moment decreases to 4 kbar and then increases again as a function of pressure. The results are explained in terms of the dynamics of the N(CH₃)₄ groups.