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Diamond capsules keep contents under pressure

Glassy carbon’s transformation lets researchers study materials under extreme pressure

by Bethany Halford
August 18, 2022


A beam penetrates a capsule with embedded argon.
Credit: Qiaoshi Zeng/Center for High Pressure Science and Technology Advanced Research

An illustration of ultraviolet light striking high-pressure argon embedded in a diamond capsule.

Inspired by exotic materials in diamonds coughed up by volcanoes, scientists have found a new way to study materials under extreme pressure. Researchers trap materials within the pores of glassy carbon at high pressure, then use extreme temperatures to transform the glassy carbon into diamond. These tiny capsules maintain their contents at high pressure even when the diamonds are brought to ambient pressure. The capsules’ contents can then be studied using electron microscopy and vacuum ultraviolet spectroscopy—techniques that are incompatible with high pressure equipment.

High pressure can profoundly change a material’s properties, says Stanford University’s Wendy L. Mao, who led the research team along with Ho-kwang Mao and Qiaoshi Zeng of China’s Center for High Pressure Science and Technology Advanced Research. “This is an important first step to demonstrate now we can actually preserve high pressure in a capsule,” she says.

The team was inspired by nature. Diamonds forming deep within the Earth’s mantle can sometimes trap minerals or fluids. These inclusions remain preserved under high pressure even when the diamond travels via volcano to the Earth’s surface. “Our process is kind of similar,” Wendy Mao says. The scientists demonstrate the capsules’ ability to preserve argon in a crystalline state at 22 GPa (Nature 2022, DOI: 10.1038/s41586-022-04955-z).

Choong-Shik Yoo, a professor at Washington State University who studies materials under extreme pressures, is impressed that the researchers accomplished this feat. In an email, he says that the study suggests the potential of high-pressure materials research to “move beyond a fundamental discovery science to a more practically viable synthesis of materials in highly metastable states far from the equilibrium at ambient conditions.”

The next step, Wendy Mao says, is to scale up the method to make larger diamond capsules and to make high-pressure phases of materials that could have practical use.



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