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.     

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.     

Density measurements of noncrystalline materials at high pressure with diamond anvil cell

We describe an x-ray absorption method for in situ density measurement of non-crystalline materials in the diamond anvil cell using a monochromatic synchrotron x-ray microbeam. Sample thickness, which is indispensable in the absorption method, can be determined precisely by extrapolating the thickness profile of the gasket obtained by x-ray absorption and diffraction measurements. Diamond deformation across the sample chamber becomes noticeable at high pressures above 10 GPa, which can be monitored with a precision better than 1%, as demonstrated by measurements on crystalline Ag. We have applied the developed method to measure densities of the classic network-forming GeO(2) glass in octahedral form at pressures up to 56 GPa. The fit to the pressure-volume data with the Birch-Murnaghan equation from 13 to 56 GPa gives parameters of V(0)=23.2+/-0.4 cm(3)mol and K=35.8+/-3.0 GPa, assuming that K(')=4. This method could be applicable for in situ determination of the density of liquids and other noncrystalline materials using a diamond anvil cell up to ultrahigh pressures.     

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.     

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.     

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.     

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.     

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.     

Cryogenic implementation of charging diamond anvil cells with H2 and D2

A cryogenic loading system for introducing H(2) and D(2) into the diamond anvil cell has been designed and constructed. The integration of pressure loading mechanism, ruby fluorescence spectrometer, and microscope camera allows for in situ tuning and calibrating the pressure. The performance of the system has been demonstrated by successful synthesis of hydride and deuteride of transition metal and rare earth metal. Our cryogenic methodology features facile start-over of loading and in situ electrical resistance measurement of as-synthesized sample.     

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.     

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.     

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.     

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.     

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.     

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.     

An in situ approach to study trace element partitioning in the laser heated diamond anvil cell

Data on partitioning behavior of elements between different phases at in situ conditions are crucial for the understanding of element mobility especially for geochemical studies. Here, we present results of in situ partitioning of trace elements (Zr, Pd, and Ru) between silicate and iron melts, up to 50 GPa and 4200 K, using a modified laser heated diamond anvil cell (DAC). This new experimental set up allows simultaneous collection of x-ray fluorescence (XRF) and x-ray diffraction (XRD) data as a function of time using the high pressure beamline ID27 (ESRF, France). The technique enables the simultaneous detection of sample melting based to the appearance of diffuse scattering in the XRD pattern, characteristic of the structure factor of liquids, and measurements of elemental partitioning of the sample using XRF, before, during and after laser heating in the DAC. We were able to detect elements concentrations as low as a few ppm level (2-5 ppm) on standard solutions. In situ measurements are complimented by mapping of the chemical partitions of the trace elements after laser heating on the quenched samples to constrain the partitioning data. Our first results indicate a strong partitioning of Pd and Ru into the metallic phase, while Zr remains clearly incompatible with iron. This novel approach extends the pressure and temperature range of partitioning experiments derived from quenched samples from the large volume presses and could bring new insight to the early history of Earth.     

A virtual experiment control and data acquisition system for in situ laser heated diamond anvil cell Raman spectroscopy

Doubled-sided laser heated diamond anvil cell methods allow simultaneous in situ confocal Raman measurements of materials up to megabar pressures and high temperatures. This paper describes a virtual control and data acquisition system developed to automate setups for simultaneous Raman/laser heating experiments. The system enables reduction of experiment time by ～90% in comparison to manual operations, allowing measurements of high quality Raman spectra of even highly reactive or diffusive samples, such as hydrogen at extreme conditions using continuous wave laser heating. These types of measurements are very difficult and often impossible to obtain in a manual operation mode. Complete data archiving and accurate control of various experimental parameters (e.g., on-the-fly temperature determination and self-adjusting data collection time to avoid signal saturation) can be done, and open up possibilities of other types of experiments involving extreme conditions.     

Creating a high temperature environment at high pressure in a gas piston cylinder apparatus

An internal heater capable of 1400 K has been developed for use with a gas piston cylinder apparatus capable of achieving in excess of 3 GPa with an argon pressure medium. The heated gas piston cylinder produces a truly hydrostatic environment for samples up to 3 mm in diameter and 8 mm in length. The apparatus can be used to study systems that are sensitive to stress or samples that cannot withstand shear tractions. The gas piston cylinder apparatus was developed in an effort to reduce experimental uncertainty in the pressure scale and has been used to improve understanding of the Bi I-II transition at 298 K. We estimate that the pressure during a high temperature soak in the gas piston cylinder can be known to within ±0.01 GPa.     

Spectrographic temperature measurement of a high power breakdown arc in a high pressure gas switch

A procedure for obtaining an approximate temperature value of conducting plasma generated during self-break closure of a RIMFIRE gas switch is described. The plasma is in the form of a breakdown arc which conducts approximately 12 kJ of energy in 1 μs. A spectrographic analysis of the trigger-section of the 6-MV RIMFIRE laser triggered gas switch used in Sandia National Laboratory's "Z-Machine" has been made. It is assumed that the breakdown plasma has sufficiently approached local thermodynamic equilibrium allowing a black-body temperature model to be applied. This model allows the plasma temperature and radiated power to be approximated. The gas dielectric used in these tests was pressurized SF(6). The electrode gap is set at 4.59 cm for each test. The electrode material is stainless steel and insulator material is poly(methyl methacrylate). A spectrum range from 220 to 550 nanometers has been observed and calibrated using two spectral irradiance lamps and three spectrograph gratings. The approximate plasma temperature is reported.