Viscosity measurements in the diamond anvil pressure cell

The viscosity of liquids can be measured in the diamond-anvil pressure cell utilizing a falling-solid sphere method and the ruby technique for pressure measurement. The pressure dependence of the viscosity of a 4:1 mixture (by volume) of methanol-ethanol was determined to 70 kilobars. The accuracy of the method is estimated from measurements made on a fluid of known viscosity.     

An induction heating diamond anvil cell for high pressure and temperature micro-Raman spectroscopic measurements

A new external heating configuration is presented for high-temperature diamond anvil cell instruments. The supporting rockers are thermally excited by induction from an externally mounted copper coil passing a 30 kHz alternating current. The inductive heating configuration therefore avoids the use of breakable wires, yet is capable of cell temperatures of 1100 K or higher. The diamond anvil cell has no resistive heaters, but uses a single-turn induction coil for elevating the temperature. The induction coil is placed near the diamonds and directly heats the tungsten carbide rockers that support the diamond. The temperature in the cell is determined from a temperature-power curve calibrated by the ratio between the intensities of the Stokes and anti-Stokes Raman lines of silicon. The high-pressure transformation of quartz to coesite is successfully observed by micro-Raman spectroscopy using this apparatus. The induction heating diamond anvil cell is thus a useful alternative to resistively heated diamond anvil cells.     

In situ Hall effect measurement on diamond anvil cell under high pressure

A method for in situ Hall effect measurement under high pressure was developed on a diamond anvil cell. The electrode was accurately integrated on one diamond anvil with regular shape. A uniform and strong magnetic field was introduced into the sample zone. The voltage errors brought by some negative effects during the measurement were well eliminated. The correction factor of the Hall coefficient, brought by the nonpoint contact between the electrode and the sample, was 4.51%. The measurement error of the magnetic field did not exceed 1%. The carrier character of ZnTe powders was studied up to 23 GPa. The evolution of conductivity with pressure was explained based on the variation of the carrier behavior.     

Preparation of W-Ta thin-film thermocouple on diamond anvil cell for in-situ temperature measurement under high pressure

In this paper, a W-Ta thin-film thermocouple has been integrated on a diamond anvil cell by thin-film deposition and photolithography methods. The thermocouple was calibrated and its thermal electromotive force was studied under high pressure. The results indicate that the thermal electromotive force of the thermocouple exhibits a linear relationship with temperature and is not associated with pressure. The resistivity measurement of ZnS powders under high pressure at different temperatures shows that the phase transition pressure decreases as the temperature increases.     

Uniform stress conditions in the diamond anvil cell at 200 kilobars

Pressure gradients in a diamond anvil cell have been measured with a 4:1 methanol:ethanol mixture as a pressure medium up to 350 kilobars. When pressure is applied rapidly, stress gradients are shown to be negligible up to 200 kilobars and probably above. With this procedure it is possible to significantly increase the precision of pressure measurements above 100 kilobars.     

Versatile type miniature diamond anvil high-pressure cell

A miniature diamond anvil high-pressure cell 42 mm in diameter, 18 mm thick, and 150 g in weight has been constructed. The cell is loaded into a piston-cylinder type pressing device with an alignment mechanism and compressed to a desired pressure. After the pressure is clamped by three screws, the cell part is taken out. Thereby, in spite of the small and simple cell, pressure can be generated easily and steadily up to 200 kbar. Because the cell is small and light enough to be mounted on a usual goniometer head, and has large openings towards both the top and bottom, it can widely be used as a versatile apparatus for research at high pressure.     

Thickness measurement of sample in diamond anvil cell

We report on an original method that measures sample thickness in a diamond anvil cell under high pressures. The method is based on two hypotheses: completely plastic deformation on the gasket and completely elastic deformation of the diamonds. This method can further eliminate the effect of diamond deformation on the thickness measurement of a sample, which permits us to measure the thickness of alumina up to 41.4 GPa.     

Cryogenic gas loading in a Mao-Bell-type diamond anvil cell for high pressure-high temperature investigations

A simple system for loading argon fluid at cryogenic temperatures in a Mao-Bell-type diamond anvil cell (DAC) has been developed. It is done in a two step process in which the piston-cylinder assembly alone is submerged in the cryogenic chamber for trapping the liquefied inert gas. Liquid nitrogen is used for condensing the argon gas. This system is now being efficiently used for loading liquid argon in the DAC for high pressure-high temperature experiments. The success rate of trapping liquefied argon in the sample chamber is about 75%. The performance of the gas loading system is successfully tested by carrying out direct conversion of pyrolitic graphite to diamond under high pressure-high temperature using laser heated DAC facility.     

IR pyrometry in diamond anvil cell above 400 K

Temperature measurements in a laser heated diamond anvil cell (DAC) are currently limited to temperatures above 1000 K using optics and detectors in the visible range. We have built a pyrometer in the IR range and expanded the lower limit of temperature detection to 400 K. The pyrometer is designed for very low thermal radiation intensities, measured sequentially through a set of bandpass filters in the range of 1.2-3.4 microm using very efficient IR photodetectors. The thermal radiation from the center of the cw Nd:YAG laser heated spot is least square fitted to a Planck curve, using a gray body approximation. Melting is detected by changes in the light scattering picture of an auxiliary He-Ne laser from the surface of the hot spot, and by a change in slope in the plot of hot spot temperature versus laser power. In this work we demonstrate measurement of the melting curve of zinc up to 25 GPa. The melting curve is in very good agreement with previous results which were taken up to 6 GPa in a large volume press.     

X-ray diffraction in the pulsed laser heated diamond anvil cell

We have developed in situ x-ray synchrotron diffraction measurements of samples heated by a pulsed laser in the diamond anvil cell at pressure up to 60 GPa. We used an electronically modulated 2-10 kHz repetition rate, 1064-1075 nm fiber laser with 1-100 μs pulse width synchronized with a gated x-ray detector (Pilatus) and time-resolved radiometric temperature measurements. This enables the time domain measurements as a function of temperature in a microsecond time scale (averaged over many events, typically more than 10,000). X-ray diffraction data, temperature measurements, and finite element calculations with realistic geometric and thermochemical parameters show that in the present experimental configuration, samples 4 μm thick can be continuously temperature monitored (up to 3000 K in our experiments) with the same level of axial and radial temperature uniformities as with continuous heating. We find that this novel technique offers a new and convenient way of fine tuning the maximum sample temperature by changing the pulse width of the laser. This delicate control, which may also prevent chemical reactivity and diffusion, enables accurate measurement of melting curves, phase changes, and thermal equations of state.     

Dynamic diamond anvil cell (dDAC): a novel device for studying the dynamic-pressure properties of materials

We have developed a unique device, a dynamic diamond anvil cell (dDAC), which repetitively applies a time-dependent load/pressure profile to a sample. This capability allows studies of the kinetics of phase transitions and metastable phases at compression (strain) rates of up to 500 GPa/s (approximately 0.16 s(-1) for a metal). Our approach adapts electromechanical piezoelectric actuators to a conventional diamond anvil cell design, which enables precise specification and control of a time-dependent applied load/pressure. Existing DAC instrumentation and experimental techniques are easily adapted to the dDAC to measure the properties of a sample under the varying load/pressure conditions. This capability addresses the sparsely studied regime of dynamic phenomena between static research (diamond anvil cells and large volume presses) and dynamic shock-driven experiments (gas guns, explosive, and laser shock). We present an overview of a variety of experimental measurements that can be made with this device.     

Energy dissipation of materials at high pressure and high temperature

We report an experimental method to study the anelastic properties of materials at high pressure and high temperature. The multianvil high pressure deformation device, used to apply a cyclic loading force onto the sample, can reach 15 GPa and 2000 K. A synchrotron x-ray radiation source provides time resolved images of the sample and reference material. The images yield stress and strain as a function of time; stresses are derived from the reference material, and strains from the sample. This method has been tested by applying a sinusoidal stress at megahertz to hertz frequency on a San Carlos olivine specimen at 5 GPa and up to 2000 K. Strain as small as 10(-5) can be resolved. We have obtained experimental results which exhibit resolvable attenuation factor (Q(-1)) and shear modulus (M) at deep Earth conditions. These results are in quantitative agreement with previously reported lower pressure data and suggest that temperature and grain size have dominating effect on these properties.     

High pressure ellipsometry: a novel method for measuring the optical properties and electronic structure of materials in diamond anvil cells

High pressure ellipsometry (HPE) method was developed for determining the index of refraction of opaque materials in a diamond anvil cell (DAC). A main difficulty in DAC-based HPE, namely, the pressure-induced birefringence developed in the diamond, was overcome enabling the extraction of the ellipsometric parameters of the sample. The method used was based on the fact that an unpolarized light is unaffected by a retarding optical element and thus reduces the number of unknown parameters in the problem. Because of technical difficulties in using unpolarized light, a linear combination of orthogonal polarizations was applied. In the experimental procedure, multiangle measurements of the ellipsometric parameter ψ are collected at each pressure and the data is fitted together with a measurement of the near normal reflectivity, in order to extract the complex index of refraction. As a test case, this procedure was used to measure the high pressure index of refraction of iron up to 30 GPa for light with wavelengths of 532 and 633 nm. From the index of refraction as a function of pressure the diamond-iron interface emissivity for different pressures was derived and from which the phase transition α → ε could be identified and characterized. The emissivity increases with pressure both at the α (0-9 GPa) and the ε phase (21-30 GPa) however decreases at the mixed α - ε (9-21 GPa) range. From the imaginary part of the index of refraction the pressure dependence of the energy skin depth of iron was extracted. It was found that the energy skin depth increases by an order of magnitude at 30 GPa relative to ambient conditions.     

Determination of the thickness of a gasket in a diamond anvil high-pressure cell

A method for determining the thickness of a gasket in a diamond anvil high-pressure cell is described. This method is based on measuring the relative position of the anvils. The gasket thickness is determined by measuring the distance between two marks, viz., virtual points “locked” to side surfaces of the anvils. The distance between the marks is determined by digital processing of microphotographs. The error of measuring the gasket thickness disregarding the deformations of the anvils is ∼1 μm. The results of measuring the gasket thickness, the aperture area, and the optical length between the working planes of the anvils for a helium-filled cell are presented. The pressure dependences of the refractive index and the volume of helium, which is compressed to a pressure of 16 GPa, that are calculated using these data are in good agreement with the published data.     

New method for measuring electrical conductivities of solids in a diamond anvil cell

A new method of measuring electrical conductivities of solids in a diamond anvil cell (DAC) has been developed. The dc method involves a four-point probe measurement. The method is suitable for measuring the electrical conductance of bulk (polycrystalline) solids or single crystals, as a function of temperature and/or pressure.     

Patterned anvils for high pressure measurements at low temperature

Multiprobe high pressure measurements require electrical leads in the sample chamber. Compared to conventional wire-based techniques, metallic tracks patterned onto the anvil surface improve reliability and ease of use, and enable novel and more demanding measurements under high pressure. We have developed new anvil designs based on sputter-deposited tracks on alumina and moissanite anvils. These anvils allow convenient and reliable measurements of electrical transport properties or of the magnetic susceptibility under hydrostatic conditions, as demonstrated by test measurements on Pb and Ca(3)Ru(2)O(7).     

Adaptation of the Bridgman anvil cell to liquid pressure mediums

The advantage of Bridgman anvil pressure cells is their wide pressure range and the large number of wires which can be introduced into the pressure chamber. In these pressure cells, soft solid pressure mediums such as steatite are used. We have succeeded in adapting the Bridgman cell to liquid pressure mediums. With this breakthrough, it is now possible to measure in very good hydrostatic pressure conditions up to 7 GPa, which is about twice the pressure attainable in piston-cylinder cells. The pressure gradient in the cell, estimated from the superconducting transition width of lead, is reduced by a factor of 5 in the liquid medium with respect to steatite. By using nonmagnetic materials for the anvils and the clamp and due to the small dimensions of the latter, our device is specially suitable for magnetotransport measurements in dilution fridges. This pressure cell has been developed to measure very fragile and brittle samples such as organic conductors. Resistivity measurements of (TMTTF)(2)BF(4) performed in a solid and a liquid pressure medium demonstrate the necessity of hydrostatic pressure conditions for the study of organic conductors at high pressures.     

A miniature cubic anvil apparatus for optical measurement under high pressure

A miniature cubic anvil apparatus was developed for optical measurement on materials in a high-pressure space of 8-10 mm(3) under high pressure, and preliminary experiments were conducted to 3.6 GPa at room temperature with optical visual observation and ruby fluorescence measurement. In the apparatus, a cubic pressure medium was squeezed with six tungsten carbide anvils, which are driven with a pair of guide blocks by tightening four loading screws. Optical access on the sample was made through holes in axial anvils and the guide blocks as well as optical windows made of Al(2)O(3) single crystals embedded in the pressure medium. The apparatus is compact and light, ~53 mm in diameter and height and ~530 g in weight, and the features of the apparatus benefit easy application of the apparatus to various types of standard optical measurement systems. The optical measurement on the sample in the high-pressure space of 8-10 mm(3) should greatly contribute to advancements of studies relevant to high-pressure behaviors of materials.     

Adaption of a diamond anvil cell to an automatic four-circle diffractometer for x-ray diffraction

A diamond anvil high-pressure device for x-ray diffraction on single crystals under hydrostatic pressures up to about 100 kilobars has been adapted to the automatic four-circle x-ray diffractometer Philips PW 1100. The mechanical adaption, the centering procedure, and quick pressure calibration on the diffractometer are described. Hints to improve the peak-to-background ratio of the intensity measurements are given.     

In situ laser heating and radial synchrotron x-ray diffraction in a diamond anvil cell

We report a first combination of diamond anvil cell radial x-ray diffraction with in situ laser heating. The laser-heating setup of ALS beamline 12.2.2 was modified to allow one-sided heating of a sample in a diamond anvil cell with an 80 W yttrium lithium fluoride laser while probing the sample with radial x-ray diffraction. The diamond anvil cell is placed with its compressional axis vertical, and perpendicular to the beam. The laser beam is focused onto the sample from the top while the sample is probed with hard x-rays through an x-ray transparent boron-epoxy gasket. The temperature response of preferred orientation of (Fe,Mg)O is probed as a test experiment. Recrystallization was observed above 1500 K, accompanied by a decrease in stress.