Diamond anvil cell

A diamond anvil cell (DAC) is a high-pressure device used in scientific experiments. It enables the compression of a small (sub-millimeter-sized) piece of material to extreme pressures, typically up to around 100–200 gigapascals, although it is possible to achieve pressures up to 770 gigapascals (7,700,000 bars / 7.7 million atmospheres).[1][2]

The device has been used to recreate the pressure existing deep inside planets to synthesise materials and phases not observed under normal ambient conditions. Notable examples include the non-molecular ice X,[3] polymeric nitrogen[4] and metallic phases of xenon[5] and potentially hydrogen.[6]

A DAC consists of two opposing diamonds with a sample compressed between the polished culets (tips). Pressure may be monitored using a reference material whose behavior under pressure is known. Common pressure standards include ruby[7] fluorescence, and various structurally simple metals, such as copper or platinum.[8] The uniaxial pressure supplied by the DAC may be transformed into uniform hydrostatic pressure using a pressure-transmitting medium, such as argon, xenon, hydrogen, helium, paraffin oil or a mixture of methanol and ethanol.[9] The pressure-transmitting medium is enclosed by a gasket and the two diamond anvils. The sample can be viewed through the diamonds and illuminated by X-rays and visible light. In this way, X-ray diffraction and fluorescence; optical absorption and photoluminescence; Mössbauer, Raman and Brillouin scattering; positron annihilation and other signals can be measured from materials under high pressure. Magnetic and microwave fields can be applied externally to the cell allowing nuclear magnetic resonance, electron paramagnetic resonance and other magnetic measurements.[10] Attaching electrodes to the sample allows electrical and magnetoelectrical measurements as well as heating up the sample to a few thousand degrees. Much higher temperatures (up to 7000 K)[11] can be achieved with laser-induced heating,[12] and cooling down to millikelvins has been demonstrated.[9]

Diamond Anvil Cell - Cross Section
Schematics of the core of a diamond anvil cell. The culets (tip) of the two diamond anvils are typically 100–250 microns across.


The operation of the diamond anvil cell relies on a simple principle:

where p is the pressure, F the applied force, and A the area. Typical culet sizes for diamond anvils are 100–250 micron, such that a very high pressure is achieved by applying a moderate force on a sample with a small area, rather than applying a large force on a large area. Diamond is a very hard and virtually incompressible material, thus minimising the deformation and failure of the anvils that apply the force.


First diamond anvil cell
The first diamond anvil cell in the NIST museum of Gaithersburg. Shown in the image above is the part which compresses the central assembly.

The study of materials at extreme conditions, high pressure and high temperature uses a wide array of techniques to achieve these conditions and probe the behavior of material while in the extreme environment. Percy Williams Bridgman, the great pioneer of high-pressure research during the first half of the 20th century, revolutionized the field of high pressures with his development of an opposed anvil device with small flat areas that were pressed one against the other with a lever-arm. The anvils were made of tungsten carbide (WC). This device could achieve pressure of a few gigapascals, and was used in electrical resistance and compressibility measurements. The principles of the DAC are similar to the Bridgman anvils but in order to achieve the highest possible pressures without breaking the anvils, they were made of the hardest known material: a single crystal diamond. The first prototypes were limited in their pressure range and there was not a reliable way to calibrate the pressure.

Following the Bridgman anvil, the diamond anvil cell became the most versatile pressure generating device that has a single characteristic that sets it apart from the other pressure devices. This provided the early high pressure pioneers with the capability to directly observe the properties of a material while under pressure. With just the use of an optical microscope, phase boundaries, color changes and recrystallization could be seen immediately, while x-ray diffraction or spectroscopy required time to expose and develop photographic film. The potential for the diamond anvil cell was realized by Alvin Van Valkenburg while he was preparing a sample for IR spectroscopy and was checking the alignment of the diamond faces.

The diamond cell was created at the National Bureau of Standards (NBS) by Charles E. Weir, Ellis R. Lippincott, and Elmer N. Bunting. Within the group each member focused on different applications of the diamond cell. Van focused on making visual observations, Charles on XRD, Ellis on IR Spectroscopy. The group was well established in each of their techniques before outside collaboration kicked off with university researchers like William A. Bassett and Taro Takahashi at the University of Rochester.

During the first experiments using diamond anvils, the sample was placed on the flat tip of the diamond, the culet, and pressed between the diamond faces. As the diamond faces were pushed closer together, the sample would be pressed and extrude out from the center. Using a microscope to view the sample, it could be seen that a smooth pressure gradient existed across the sample with the outer most portions of the sample acting as a kind of gasket. The sample was not evenly distributed across the diamond culet but localized in the center due to the "cupping" of the diamond at higher pressures. This cupping phenomenon is the elastic stretching of the edges of the diamond culet, commonly referred to as the "shoulder height". Many diamonds were broken during the first stages of producing a new cell or any time an experiment is pushed to higher pressure. The NBS group was in a unique position where almost endless supplies of diamonds were available to them. Custom officials occasionally confiscated diamonds from people attempting to smuggle them into the country. Disposing of such valuable confiscated materials could be problematic given rules and regulations. A solution was simply to make such materials available to people at other government agencies if they could make a convincing case for their use. This became an unrivaled resource as other teams at the University of Chicago, Harvard University and General Electric entered the high pressure field.

During the following decades DACs have been successively refined, the most important innovations being the use of gaskets and the ruby pressure calibration. The DAC evolved to be the most powerful lab device for generating static high pressure.[13] The range of static pressure attainable today extends to 640 GPa, much higher than the estimated pressures at the Earth's center (~360 GPa).[14]


There are many different DAC designs but all have four main components:

Force-generating device

Relies on the operation of either a lever arm, tightening screws, or pneumatic or hydraulic pressure applied to a membrane. In all cases the force is uniaxial and is applied to the tables (bases) of the two anvils.

Two opposing diamond anvils

Made of high gem quality, flawless diamonds, usually with 16 facets, they typically weigh 1/8 to 1/3 carat (25 to 70 mg). The culet (tip) is ground and polished to a hexadecagonal surface parallel to the table. The culets of the two diamonds face one another, and must be perfectly parallel in order to produce uniform pressure and to prevent dangerous strains. Specially selected anvils are required for specific measurements—for example, low diamond absorption and luminescence is required in corresponding experiments.


A gasket used in a diamond anvil cell experiment is a thin metal foil, typically 0.3 mm in thickness, which is placed in between the diamonds. Desirable materials for gaskets are strong, stiff metals such as rhenium or tungsten. Steel is frequently used as a cheaper alternative for low pressure experiments. The above-mentioned materials cannot be used in radial geometries where the x-ray beam must pass through the gasket. Since they are not transparent to x-rays, if x-ray illumination through the gasket is required, lighter materials such as beryllium, boron nitride,[15] boron[16] or diamond[17] are used as a gasket. Gaskets are preindented by the diamonds and a hole is drilled in the center of the indentation to create the sample chamber.

Pressure-transmitting medium

The pressure transmitting medium is the compressible fluid that fills the sample chamber and transmits the applied force to the sample. Hydrostatic pressure is preferred for high-pressure experiments because variation in strain throughout the sample can lead to distorted observations of different behaviors. In some experiments stress and strain relationships are investigated and the effects of non-hydrostatic forces are desired. A good pressure medium will remain a soft, compressible fluid to high pressure.

  • Gases: He, Ne, Ar, N2
  • Liquids: 4:1 Methanol/Ethanol, Silicone Oil, Fluorinert, Daphne 7474 Cyclohexane
  • Solids: NaCl

The full range of techniques that are available has been summarized in a tree diagram by William Bassett. The ability to utilize any and all of these techniques hinges on being able to look through the diamonds which was first demonstrated by visual observations.

Measuring pressure

The two main pressure scales used in static high-pressure experiments are X-ray diffraction of a material with a known equation of state and measuring the shift in ruby fluorescence lines. The first began with NaCl, for which the compressibility has been determined by first principles in 1968. The major pitfall of this method of measuring pressure is that you need X-rays. Many experiments do not require X-rays and this presents a major inconvenience to conduct both the intended experiment and a diffraction experiment. In 1971, the NBS high pressure group was set in pursuit of a spectroscopic method for determining pressure. It was found that the wavelength of ruby fluorescence emissions change with pressure, this was easily calibrated against the NaCl scale.[18][19]

Once pressure could be generated and measured it quickly became a competition for which cells can go the highest. The need for a reliable pressure scale became more important during this race. Shock-wave data for the compressibilities of Cu, Mo, Pd and Ag were available at this time and could be used to define equations of states up to Mbar pressure. Using these scales these pressures were reported: 1.2 Mbar (120 GPa) in 1976, 1.5 Mbar (150 GPa) in 1979, 2.5 Mbar (250 GPa) in 1985, and 5.5 Mbar (550 GPa) in 1987.

Both methods are continually refined and in use today. However, the ruby method is less reliable at high temperature. Well defined equations of state are needed when adjusting temperature and pressure, two parameters that affect the lattice parameters of materials.


Prior to the invention of the diamond anvil cell, static high-pressure apparatus required large hydraulic presses which weighed several tons and required large specialized laboratories. The simplicity and compactness of the DAC meant that it could be accommodated in a wide variety of experiments. Some contemporary DACs can easily fit into a cryostat for low-temperature measurements, and for use with a superconducting electromagnet. In addition to being hard, diamonds have the advantage of being transparent to a wide range of the electromagnetic spectrum from infrared to gamma rays, with the exception of the far ultraviolet and soft X-rays. This makes the DAC a perfect device for spectroscopic experiments and for crystallographic studies using hard X-rays.

A variant of the diamond anvil, the hydrothermal diamond anvil cell (HDAC) is used in experimental petrology/geochemistry for the study of aqueous fluids, silicate melts, immiscible liquids, mineral solubility and aqueous fluid speciation at geologic pressures and temperatures. The HDAC is sometimes used to examine aqueous complexes in solution using the synchrotron light source techniques XANES and EXAFS. The design of HDAC is very similar to that of DAC, but it is optimized for studying liquids.[20]

Innovative uses

An innovative use of the diamond anvil cell is testing the sustainability and durability of life under high pressures, including the search for life on extrasolar planets. Testing portions of the theory of panspermia (a form of interstellar travel) is one application of DAC. When interstellar objects containing life-forms impact a planetary body, there is high pressure upon impact and the DAC can replicate this pressure to determine if the organisms could survive. Another reason the DAC is applicable for testing life on extrasolar planets is that planetary bodies that hold the potential for life may have incredibly high pressure on their surface.

In 2002, scientists at the Carnegie Institution of Washington examined the pressure limits of life processes. Suspensions of bacteria, specifically Escherichia coli and Shewanella oneidensis, were placed in the DAC, and the pressure was raised to 1.6 GPa, which is more than 16,000 times Earth's surface pressure (985 hPa). After 30 hours, only about 1% of the bacteria survived. The experimenters then added a dye to the solution. If the cells survived the squeezing and were capable of carrying out life processes, specifically breaking down formate, the dye would turn clear. 1.6 GPa is such great pressure that during the experiment the DAC turned the solution into ice-IV, a room-temperature ice. When the bacteria broke down the formate in the ice, liquid pockets would form because of the chemical reaction. The bacteria were also able to cling to the surface of the DAC with their tails.[21]

Skeptics debated whether breaking down formate is enough to consider the bacteria living. Art Yayanos, an oceanographer at the Scripps Institute of Oceanography in La Jolla, California, believes an organism should only be considered living if it can reproduce. Subsequent results from independent research groups[22] have shown the validity of the 2002 work. This is a significant step that reiterates the need for a new approach to the old problem of studying environmental extremes through experiments. There is practically no debate whether microbial life can survive pressures up to 600 MPa, which has been shown over the last decade or so to be valid through a number of scattered publications.[23]

Similar tests were performed with a low-pressure (0.1–600 MPa) diamond anvil cell, which has better imaging quality and signal collection. The studied microbes, Saccharomyces cerevisiae (baker's yeast), withstood pressures of 15–50 MPa, and died at 200 MPa.[24]

Single crystal X-ray diffraction

Good single crystal diffraction experiments in diamond anvil cells require sample stage to rotate on the vertical axis, omega. Most diamond anvil cells do not feature a large opening that would allow the cell to be rotated to high angles, a 60 degrees opening is considered sufficient for most crystals but larger angles are possible. The first cell to be used for single crystal experiments was designed by a graduate student at the University of Rochester, Leo Merrill. The cell was triangular with beryllium seats that the diamonds were mounted on; the cell was pressurized with screws and guide pins holding everything in place.

High-temperature techniques

High-pressure experiments
Conditions achievable using different methods of static pressure generation.

Heating in diamond-anvil cells is typically done by two means, external or internal heating. External heating is defined as heating the anvils and would include a number of resistive heaters that are placed around the diamonds or around the cell body. The complementary method does not change the temperature of the anvils and includes fine resistive heaters placed within the sample chamber and laser heating. The main advantage to resistive heating is the precise measurement of temperature with thermocouples, but the temperature range is limited by the properties of the diamond which will oxidize in air at 700 °C [25] The use of an inert atmosphere can extend this range above 1000 °C. With laser heating the sample can reach temperature above 5000 °C, but the minimum temperature that can be measured when using a laser-heating system is ~1200 °C and the measurement is much less precise. Advances in resistive heating are closing the gap between the two techniques so that systems can be studied from room temperature to beyond 5700 °C with the combination of the two.

Gas loading


The pressure transmitting medium is an important component in any high-pressure experiment. The medium fills the space within the sample 'chamber' and applies the pressure being transmitted to the medium onto the sample. In a good high-pressure experiment, the medium should maintain a homogeneous distribution of pressure on the sample. In other words, the medium must stay hydrostatic to ensure uniform compressibility of the sample. Once a pressure transmitting medium has lost its hydrostaticity, a pressure gradient forms in the chamber that increases with increasing pressure. This gradient can greatly affect the sample, compromising results. The medium must also be inert, as to not interact with the sample, and stable under high pressures. For experiments with laser heating, the medium should have low thermal conductivity. If an optical technique is being employed, the medium should be optically transparent and for x-ray diffraction, the medium should be a poor x-ray scatterer – as to not contribute to the signal.

Some of the most commonly used pressure transmitting media have been sodium chloride, silicone oil, and a 4:1 methanol-ethanol mixture. Sodium chloride is easy to load and is used for high-temperature experiments because it acts as a good thermal insulator. The methanol-ethanol mixture displays good hydrostaticity to about 10 GPa and with the addition of a small amount of water can be extended to about 15 GPa.[25]

For pressure experiments that exceed 10 GPa, noble gases are preferred. The extended hydrostaticity greatly reduces the pressure gradient in samples at high pressure. Noble gases, such as helium, neon, and argon are optically transparent, thermally insulating, have small X-ray scattering factors and have good hydrostaticity at high pressures. Even after solidification, noble gases provide quasihydrostatic environments.

Argon is used for experiments involving laser heating because it is chemically insulating. Since it condenses at a temperature above that of liquid nitrogen, it can be loaded cryogenically. Helium and neon have low X-ray scattering factors and are thus used for collecting X-ray diffraction data. Helium and neon also have low shear moduli; minimizing strain on the sample.[26] These two noble gases do not condense above that of liquid nitrogen and cannot be loaded cryogenically. Instead, a high-pressure gas loading system has been developed that employs a gas compression method.[27]


In order to load a gas as a sample of pressure transmitting medium, the gas must be in a dense state, as to not shrink the sample chamber once pressure is induced. To achieve a dense state, gases can be liquefied at low temperatures or compressed. Cryogenic loading is a technique that uses liquefied gas as a means of filling the sample chamber. The DAC is directly immersed into the cryogenic fluid that fills the sample chamber. However, there are disadvantages to cryogenic loading. With the low temperatures indicative of cryogenic loading, the sample is subjected to temperatures that could irreversibly change it. Also, the boiling liquid could displace the sample or trap an air bubble in the chamber. It is not possible to load gas mixtures using the cryogenic method due to the different boiling points of most gases. Gas compression technique densifies the gases at room temperature. With this method, most of the problems seen with cryogenic loading are fixed. Also, loading gas mixtures becomes a possibility. The technique uses a vessel or chamber in which the DAC is placed and is filled with gas. Gases are pressurized and pumped into the vessel with a compressor. Once the vessel is filled and the desired pressure is reached the DAC is closed with a clamp system run by motor driven screws.


  • High-pressure vessel: Vessel in which the diamond anvil cell is loaded.
  • Clamp device seals the DAC; which is tightened by closure mechanism with motor driven screws.
  • PLC (programmable logic controller): Controls air flow to the compressor and all valves. The PLC ensures that valves are opened and closed in the correct sequence for accurate loading and safety.
  • Compressor: Responsible for compression of the gas. The compressor employs a dual-stage air-driven diaphragm design that creates pressure and avoids contamination. Able to achieve 207MPa of pressure.
  • Valves: Valves open and close via the PLC to regulate which gases enter the high-pressure vessel.
  • Burst disks: Two burst disks in the system – one for the high-pressure system and one for the low-pressure system. These disks act as a pressure relief system that protects the system from over-pressurization
  • Pressure transducers: A pressure sensor for the low- and high-pressure systems. Produces a 0–5V output over their pressure range.
  • Pressure meters: Digital displays connected to each pressure transducer and the PLC system.
  • Vacuum pump and gauges: Cleans the system (by evacuation) before loading.
  • Optical system: Used visual observation; allowing in situ observations of gasket deformation.
  • Ruby fluorescence system: Pressure in the sample chamber can be measured during loading using an online ruby fluorescence system. Not all systems have an online ruby fluorescence system for in situ measuring. However, being able to monitor the pressure within the chamber while the DAC is being sealed is advantageous – ensuring the desired pressure is reached (or not over-shot). Pressure is measured by the shift in the laser induced luminescence of rubies in the sample chamber.

Laser heating


The development of laser heating began only 8 years after Charles Weir, of the National Bureau of Standards (NBS), made the first diamond anvil cell and Alvin Van Valkenburg, NBS, realized the potential of being able to see the sample while under pressure. William Bassett and his colleague Taro Takahashi focused a laser beam on the sample while under pressure. The first laser heating system used a single 7 joule pulsed ruby laser that heated the sample to 3000 °C while at 260 kilobars. This was sufficient to convert graphite to diamond.[28] The major flaws within the first system related to control and temperature measurement.

Temperature measurement was initially done by Basset using an optical pyrometer to measure the intensity of the incandescent light from the sample. Colleagues at UC Berkeley were better able to utilize the black body radiation and more accurately measure the temperature.[29] The hot spot produced by the laser also created large thermal gradients in between the portions of sample that were hit by the focused laser and those that were not. The solution to this problem is ongoing but advances have been made with the introduction of a double-sided approach.

Double-sided heating

The use of two lasers to heat the sample reduces the axial temperature gradient, this which allows for thicker samples to be heated more evenly. In order for a double-sided heating system to be successful it is essential that the two lasers are aligned so that they are both focused on the sample position. For in situ heating in diffraction experiments, the lasers need to be focused to the same point in space where the X-ray beam is focused.

Laser heating systems at synchrotron facilities

The European Synchrotron Radiation Facility (ESRF) as well as many other synchrotron facilities as the three major synchrotron user facilities in the United States all have beamlines equipped with laser heating systems. The respective beamlines with laser heating systems are at the ESRF ID27[30] and ID24;[31] at the Advanced Photon Source (APS), 13-ID-D GSECARS and 16-ID-B HP-CAT; at the National Synchrotron Light Source, X17B3; and at the Advanced Light Source, 12.2.2. Laser heating has become a routine technique in high-pressure science but the reliability of temperature measurement is still controversial.

Temperature measurement

In the first experiments with laser heating, temperature came from a calibration of laser power made with known melting points of various materials. When using the pulsed ruby laser this was unreliable due to the short pulse. YAG lasers quickly become the standard, heating for relatively long duration, and allowing observation of the sample throughout the heating process. It was with the first use of YAG lasers that Bassett used an optical pyrometer to measure temperatures in the range of 1000 °C to 1600 °C.[28] The first temperature measurements had a standard deviation of 30 °C from the brightness temperature, but due to the small sample size was estimated to be 50 °C with the possibility that the true temperature of the sample being was 200 °C higher than that of the brightness measurement. Spectrometry of the incandescent light became the next method of temperature measurement used in Bassett's group. The energy of the emitted radiation could be compared to known black body radiation spectra to derive a temperature. Calibration of these systems is done with published melting points or melting points as measured by resistive heating.

Application of laser heating

Laser heating is used to heat micrograms of sample in diamond-anvil cells when studying matter under extreme conditions. This typically means one of four things:

  • Thermal equation of states
    • Measuring the pressure-volume-temperature state of a material. In DAC work, this is done by applying pressure with the diamond anvils, applying temperature with lasers/resistive heaters, and measuring the volume response with X-ray diffraction. The thermal expansion and compressibility can then be defined in an equation of state with the independent variable of volume.
  • High-pressure/temperature synthesis
    • Using a diamond-anvil cell and laser heating to reach high pressures and temperatures achieve novel synthesis routes not accessible at ambient pressure that can produce unique high-pressure phases.
  • Phase transition studies
    • Providing excess kinetic energy to a sample in order to observe a kinetically unfavorable transition. Developing phase diagrams over the high-pressure range.
  • High-pressure melting
    • Measuring the dependence of the melting point on pressure. Pressure commonly elevates the melting point of solids.

See also


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External links

Aggregated diamond nanorod

Aggregated diamond nanorods, or ADNRs, are a nanocrystalline form of diamond, also known as nanodiamond or hyperdiamond.

Amorphous carbonia

Amorphous carbonia, also called a-carbonia or a-CO2, is an exotic amorphous solid form of carbon dioxide that is analogous to amorphous silica glass. It was first made in the laboratory in 2006 by subjecting dry ice to high pressures (40-48 gigapascal, or 400,000 to 480,000 atmospheres), in a diamond anvil cell. Amorphous carbonia is not stable at ordinary pressures—it quickly reverts to normal CO2.While normally carbon dioxide forms molecular crystals, where individual molecules are bound by Van der Waals forces, in amorphous carbonia a covalently bound three-dimensional network of atoms is formed, in a structure analogous to silicon dioxide or germanium dioxide glass.

Mixtures of a-carbonia and a-silica may be a prospective very hard and stiff glass material stable at room temperature. Such glass may serve as protective coatings, e.g. in microelectronics.

The discovery has implications for astrophysics, as interiors of massive planets may contain amorphous solid carbon dioxide.

Disodium helide

Disodium helide (Na2He) is a compound of helium and sodium that is stable at high pressures above 113 gigapascals (1,130,000 bar). It was first predicted using USPEX code and then synthesised in 2016.Na2He was predicted to be thermodynamically stable over 160 GPa and dynamically stable over 100 GPa. This means it should be possible to form at the higher pressure and then decompress to 100 GPa, but below that it would decompose. Compared with other binary compounds of other elements and helium, it was predicted to be stable at the lowest pressure of any such combination. So that for example a helium-potassium compound is predicted to require much higher pressures of the order of terapascals.

Disodium helide has a cubic crystal structure, resembling fluorite. At 300 GPa the edge of a unit cell of the crystal has a = 3.95 Å. Each unit cell contains four helium atoms on the centre of the cube faces and corners, and eight sodium atoms at coordinates a quarter cell in from each face. Double electrons (2e−) are positioned on each edge and the centre of the unit cell. Each pair of electrons is spin paired. The presence of these isolated electrons makes this an electride. The helium atoms do not participate in any bonding. However the electron pairs can be considered as an eight-centre two-electron bond.

The material was synthesised in a diamond anvil cell at 130 GPa heated to 1,500 K with a laser. Disodium helide is predicted to be an insulator and transparent. The sodium atoms have a Bader charge of +0.6, the helium charge is -0.15 and the two-electron spots are -1.1. So this phase could be called disodium helium electride. The solid is an electrical insulator and is predicted to be transparent. Disodium helide melts at a high temperature near 1,500 K, much higher than the melting point of sodium. When decompressed, it can keep its form as low as 113 GPa.

Ellis R. Lippincott Award

The Ellis R. Lippincott Award is awarded annually to recognize "an individual who has made significant contributions to vibrational spectroscopy as judged by his or her influence on other scientists."

It was jointly established in 1975 by The Optical Society, The Coblentz Society, and The Society for Applied Spectroscopy. The award honors Ellis R. Lippincott, a vibrational spectroscopist who worked at the University of Maryland. Lippincott was one of the developers of the Diamond anvil cell, which is used in high pressure research.


Ferropericlase or magnesiowüstite is a magnesium/iron oxide ((Mg,Fe)O) that is interpreted to be one of the main constituents of the Earth's lower mantle together with silicate perovskite, a magnesium/iron silicate with a perovskite structure. Ferropericlase has been found as inclusions in a few natural diamonds. An unusually high iron content in one suite of diamonds has been associated with an origin from the lowermost mantle. Discrete ultralow-velocity zones in the deepest parts of the mantle, near the Earth's core, are thought to be blobs of ferropericlase, as seismic waves are significantly slowed down as they pass through them, and ferropericlase is known to have this effect at the high pressures and temperatures found deep within the Earth's mantle. In May 2018, ferropericlase was shown to be anisotropic in specific ways in the high pressures of the lower mantle, and these anisotropies may help seismologists and geologists to confirm whether those ultrslow-velocity zones are indeed ferropericlase, by passing seismic waves through them from various different directions and observing the exact amount of change in the velocity of those waves.

High pressure

In science and engineering the study of high pressure examines its effects on materials and the design and construction of devices, such as a diamond anvil cell, which can create high pressure. By high pressure is usually meant pressures of thousands (kilobars) or millions (megabars) of times atmospheric pressure (about 1 bar or 100,000 Pa).

Iron pentahydride

Iron pentahydride FeH5 is a superhydride compound of iron and hydrogen, stable under high pressures. It is important because it contains atomic hydrogen atoms that are not bonded into smaller molecular clusters, and may be a superconductor. Pairs of hydrogen atoms are not bonded together into molecules. FeH5 has been made by compressing a flake of iron with hydrogen in a diamond anvil cell to a pressure of 130 GPa and heating to below 1500K. When decompressed to 66 GPa it decomposes to solid FeH3.

The unit cell is tetragonal with symmetry I4/mmm.

Isotopically pure diamond

An isotopical pure diamond is a type of diamond that is composed entirely of one isotope of carbon. Isotopically pure diamonds have been manufactured from either the more common carbon isotope with mass number 12 (abbreviated as 12C) or the less common 13C isotope. Compared to natural diamonds that are composed of a mixture of 12C and 13C isotopes, isotopically pure diamonds possess improved characteristics such as increased thermal conductivity. Thermal conductivity of diamonds is at a minimum when 12C and 13C are in a ratio of 1:1 and reaches a maximum when the composition is 100% 12C or 100% 13C.

Metallic hydrogen

Metallic hydrogen is a phase of hydrogen in which it behaves like an electrical conductor. This phase was predicted in 1935 on theoretical grounds by Eugene Wigner and Hillard Bell Huntington.At high pressure and temperatures, metallic hydrogen can exist as a liquid rather than a solid, and researchers think it might be present in large quantities in the hot and gravitationally compressed interiors of Jupiter, Saturn, and in some exoplanets.

Mineral physics

Mineral physics is the science of materials that compose the interior of planets, particularly the Earth. It overlaps with petrophysics, which focuses on whole-rock properties. It provides information that allows interpretation of surface measurements of seismic waves, gravity anomalies, geomagnetic fields and electromagnetic fields in terms of properties in the deep interior of the Earth. This information can be used to provide insights into plate tectonics, mantle convection, the geodynamo and related phenomena.

Laboratory work in mineral physics require high pressure measurements. The most common tool is a diamond anvil cell, which uses diamonds to put a small sample under pressure that can approach the conditions in the Earth's interior.

National Geophysical Research Institute

The National Geophysical Research Institute (NGRI) is a geoscientific research organization established in 1961 under the Council of Scientific and Industrial Research (CSIR), India's largest Research and Development organization. It is supported by more than 200 scientists and other technical staff whose research activities are published in several journals of national and international interest.

Research areas covered by this institute include hydrocarbon and coal exploration, mineral exploration, deep seismic sounding studies, exploration and management of groundwater resources, earthquake hazard assessment, structure of earth's interior and its evolution (theoretical studies), geophysical instrument development and geothermal exploration.

The major facilities available at NGRI include:

Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometer (LA-MC-ICPMS) with clean chemistry laboratory facility.

Mineral Physics Laboratory with high-pressure Diamond Anvil Cell (DAC), ultra high resolution (0.02/cm) double monochorometer, and micro-Raman spectrometer.

High-pressure laboratory consisting of Keithly electrometer, strain-measuring sensors, universal testing machine (100 tons), and Bridgeman-Birch high-pressure apparatus.

In-situ stress measurement facility consisting of hydraulic equipment.

Rock magnetism laboratory consisting of astatic magnetometer, digital spinner magnetometer, alternating magnetic field and thermal demagnetizers, high-field and low-field hysteresis and susceptibility meter.

Geochemical laboratory consisting of fully automated X-ray Fluorescence Spectrometer (XRF), Atomic Absorption Spectrometer, Inductively Coupled Plasma Mass Spectrometer (ICPMS), and Electron Probe Micro Analyzer (EPMA).

Geochronology and isotope geochemistry laboratory with facilities for Rb-Sr, Sm-Nd, and Pb-Pb analyses.

EM, Resistivity, and IP Model Laboratories.

Continuous Flow Isotope Ratio Mass Spectrometer Laboratory (CFIRMS).

Helium Emanometry, Heatflow and Radiometry Laboratory.

Tritium and carbon dating laboratory for groundwater.

Centralized computing facilities: PC-LAN and an array of Sun Workstations.

Thermoluminescence (TR) Optically Stimulated Luminescence (OSL) dating facility.

Absolute Gravity Lab.

Airborne magnetic and electromagnetic surveys.


Polycarbonyl, (also known as polymeric-CO, p-CO or poly-CO) is a solid metastable and explosive polymer of carbon monoxide. The polymer is produced by exposing carbon monoxide to high pressures. The structure of the solid appears amorphous, but may include a zig zag of equally spaced CO groups.

Pressure-induced hydration

Pressure-induced hydration (PIH), also known as “super-hydration”, is a special case of pressure-induced insertion whereby water molecules are injected into the pores of microporous materials. In PIH, a microporous material is placed under pressure in the presence of water in the pressure-transmitting fluid of a diamond anvil cell.Early physical characterization and initial diffraction experiments in zeolites were followed by the first unequivocal structural characterization of PIH in the small-pore zeolite natrolite (Na16Al16Si24O80 x 16H2O), which in its fully super-hydrated form, Na16Al16Si24O80 x 32H2O, doubles the amount of water it contains in its pores.

PIH has now been demonstrated in natrolites containing Li, K, Rb and Ag as monovalent cations as well as in large-pore zeolites, pyrochlores, clays and graphite oxide.Using the noble gases Ar, Kr, and Xe as well as CO2 as pressure-transmitting fluids, researchers have prepared and structurally characterized the products of reversible, pressure-induced insertion of Ar Kr, and CO2 as well as the irreversible insertion of Xe and water.

Pressure experiment

Pressure experiments are experiments performed at pressures lower or higher than atmospheric pressure, called low-pressure experiments and high-pressure experiments, respectively. Pressure experiment are necessary because substances behave differently at different pressures. For example, water boils at a lower temperature at lower pressures. The equipment used for pressure experiments depends on whether the pressure is to be increased or decreased and by how much. A vacuum pump is used to remove the air out of a vacuum vessel for low-pressure experiments. High-pressures can be created with a piston-cylinder apparatus, up to 5 GPa (50 000 bar) and ~2000 °C. The piston is shifted with hydraulics, decreasing the volume inside the confining cylinder and increasing the pressure. For higher pressures, up to 25 GPa, a multi-anvil cell is used and for even higher pressures the diamond anvil cell. The diamond anvil cell is used to create extremely high pressures, as much as a million atmospheres (101 GPa), though only over a small area. The current record is 560 GPa, but the sample size is confined to the order of tens of micrometres (10−5 m).

Ranga Dias (scientist)

Ranga Dias is a Sri Lankan born scientist, physicist, researcher currently working in the Lyman Laboratory of Physics at Harvard University.He was graduated from Department of Physics, Colombo University Sri Lanka and moved to Washington, USA for Ph.D. work at Washington State University in the field of extreme condensed matter physics. During his Ph.D. research at Washington State University he discovered a new class of highly conducting metallic and superconducting polymers; his CV lists 7 papers published since 2011 in the fields of solid state physics and extreme high pressure, while 16 are listed at ORCID.In January 2017, scientist Dias and Isaac F. Silvera (Thomas D. Cabot Professor of the Natural Sciences) at Harvard University reported the creation of metallic hydrogen in a laboratory. They claimed to have gathered experimental evidence that solid metallic hydrogen had been synthesised, using a diamond anvil cell.According to the reports in Science and the Harvard Gazette, the two physicists claimed to have crushed hydrogen under immense pressures, whereupon the gas became a shiny metal, a feat that physicists have been trying to accomplish for more than 80 years. Despite the claim, an article in Nature names five physicists who are not convinced that hydrogen has been squeezed to a metallic form inside a diamond-tipped anvil in this work.

Russell J. Hemley

Russell Julian Hemley (26 October 1954, Berkeley, California) is an American geophysicist, solid-state physicist, and physical chemist.

Hemley grew up in California, Colorado and Utah. He studied chemistry and philosophy at Wesleyan University with bachelor's degree in 1977 and then physical chemistry at Harvard University with master's degree in 1980 and Ph.D. in 1983. As a postdoc he was at Harvard University and was from 1984 to 1987 a Carnegie fellow at the Geophysical Laboratory of the Carnegie Institution in Washington D.C. From 1987 to 2016 he was a staff member of the Geophysical Laboratory, where he was from 2007 to 2013 the director.In the academic year 1991–1992 he was a visiting scientist at the Johns Hopkins University and in 1996 and again in 1999 at the École normale supérieure de Lyon.

Hemley's research deals with the properties of matter under high pressure with applications in geophysics, geochemistry and planetology, as well as applications in solid-state physics, chemistry, and pressure effects on biomolecules and biological systems; the applications in physics include hydrogen under pressure in the megabar range, generation of novel superconductors, magnetic structures, glasses and superhard materials under high pressure; the applications in chemistry include new compounds under high pressure. Helmley's research has been experimental (e.g. high-pressure studies with spectroscopic methods and generating high pressures with laser-heated diamond anvil cell) and theoretical; he used theory to develop high-pressure experimental methods in conjunction with microscopic laser-optical and X-ray diffraction analysis in situ from synchrotron radiation sources. Hemley worked in the late 1980s with Ho-Kwang Mao, who became famous for his 1976 work with Peter M. Bell on extension of the laboratory pressure range up to pressures over 1 megabar. Hemley, Mao, and Bell investigated not only minerals under pressures corresponding to those in the Earth's interior but also gases and liquids under pressures believed to exist in the interiors of gas giants such as Jupiter and Saturn. In particular, they investigated the behavior of hydrogen at pressures in the megabar range.Hemley has published over 490 articles as an author or co-author and has been awarded several patents.Hemley received in 2005 the Balzan Prize jointly with Ho-Kwang Mao and in 2009 the Bridgman Award. He is a fellow of the American Academy of Arts and Sciences, the American Geophysical Union and the American Physical Society. In 2001 he was elected a member of the National Academy of Sciences. Since 2003 he has been a member of the JASON Defense Advisory Group.


Seifertite is a silicate mineral with the formula SiO2 and is one of the densest polymorphs of silica. It has only been found in Martian and lunar meteorites, where it is presumably formed from either tridymite or cristobalite – other polymorphs of quartz – as a result of heating during the atmospheric re-entry and impact to the Earth, at an estimated minimal pressure of 35 GPa. It can also be produced in the laboratory by compressing cristobalite in a diamond anvil cell to pressures above 40 GPa. The mineral is named after Friedrich Seifert (born 1941), the founder of the Bayerisches Geoinstitut at University of Bayreuth, Germany, and is officially recognized by the International Mineralogical Association.Seifertite forms micrometre-sized crystalline lamellae embedded into a glassy SiO2 matrix. The lamellae are rather difficult to analyze, as they vitrify within seconds under laser or electron beams used for standard Raman spectroscopy or electron-beam microanalysis, even at much reduced beam intensities. Nevertheless, it was possible to verify that it is mainly composed of SiO2 with minor inclusions of Na2O (0.40 wt.%) and Al2O3 (1.14 wt.%). X-ray diffraction reveals that the mineral has scrutinyite (α-PbO2) type structure with an orthorhombic symmetry and Pbcn or Pb2n space group. Its lattice constants a = 4.097, b = 5.0462, c = 4.4946, Z = 4 correspond to the density of 4.294 g/cm3, which is among the highest for any forms of silica (for example, density of quartz is 2.65 g/cm3). Only stishovite has a comparable density of about 4.3 g/cm3.

Voitenko compressor

The Voitenko compressor is a shaped charge adapted from its original purpose of piercing thick steel armour to the task of accelerating shock waves. It was proposed by Anatoly Emelyanovich Voitenko (Анатолий Емельянович Войтенко), a Ukrainian-Russian scientist, in 1964. It slightly resembles a wind tunnel.

The Voitenko compressor initially separates a test gas from a shaped charge with a malleable steel plate. When the shaped charge detonates, most of its energy is focused on the steel plate, driving it forward and pushing the test gas ahead of it. Ames Research Center translated this idea into a self-destroying shock tube. A 30-kilogram (66 lb) shaped charge accelerated the gas in a 3-cm glass-walled tube 2 meters in length. The velocity of the resulting shock wave was a phenomenal 67 km/s (220,000 ft/s). The apparatus exposed to the detonation was, of course, completely destroyed, but not before useful data were extracted. In a typical Voitenko compressor, a shaped charge accelerates hydrogen gas, which in turn accelerates a thin disk up to about 40 km/s. A slight modification to the Voitenko compressor concept is a super-compressed detonation, a device that uses a compressible liquid or solid fuel in the steel compression chamber instead of a traditional gas mixture. A further extension of this technology is the explosive diamond anvil cell, utilizing multiple opposed shaped-charge jets projected at a single steel-encapsulated fuel, such as hydrogen. The fuels used in these devices, along with the secondary combustion reactions and long blast impulse, produce similar conditions to those encountered in fuel-air and thermobaric explosives.This method of detonation produces energies over 100 keV (~109 K temperatures), suitable not only for nuclear fusion, but other higher-order quantum reactions as well. The UTIAS explosive-driven-implosion facility was used to produce stable, centered and focused hemispherical implosions to generate neutrons from D–D reactions. The simplest and most direct method proved to be in a predetonated stoichiometric mixture of deuterium and oxygen. The other successful method was using a miniature Voitenko-type compressor, where a plane diaphragm was driven by the implosion wave into a secondary small spherical cavity that contained pure deuterium gas at one atmosphere. In brief, PETN solid explosive is used to form a hemispherical shell (3–6 mm thick) in a 20-cm diameter hemispherical cavity milled in a massive steel chamber. The remaining volume is filled with a stoichiometric mixture of (H2 or D2 and O2). This mixture is detonated by a very short thin exploding wire located at the geometric center. The arrival of the detonation wave at the spherical surface instantly and simultaneously fires the explosive liner. The detonation wave in the explosive liner hits the metal cavity, reflects, and implodes on the preheated burnt gases, focuses at the center of the hemisphere (50 microseconds after the initiation of the exploding wire) and reflects, leaving behind a very small pocket (1 mm) of extremely high-temperature, high-pressure and high-density plasma.

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