Germanium Conducts Electricity Under Pressure

Researchers have discovered that germanium undergoes a structural change into a conductive metal at 66 GPa.

AsianScientist (Apr. 6, 2011) – Although its name may make many people think of the germanium flower, the element germanium is part of a frequently studied group of elements, called IVa, which could have applications for next-generation computer architecture as well as implications for fundamental condensed matter physics.

New research conducted by Xiao-Jia Chen, Viktor Struzhkin, and Ho-Kwang (Dave) Mao from Geophysical Laboratory at Carnegie Institution for Science, along with collaborators from the University of Hong Kong, reveals details of the element’s transitions under pressure. Their results show extraordinary agreement with the predictions of modern condensed matter theory.

Germanium (atomic number 32) is used in fiber-optic systems, specialized camera and microscope lenses, circuitry, and solar cells. Under ambient conditions it is brittle and semiconductive.

The team’s research, published in Physical Review Letters, discovered that under pressure of 66 GPa (about 650,000 atmospheres), germanium undergoes a structural change into a metallic state — meaning it conducts electricity.

Germanium then undergoes another structural change under pressure of 90 GPa (about 890,000 atmospheres). These findings matched theoretical predictions about the element’s behavior under extreme pressure.

“A series of phase transitions was observed on compression of germanium that creates structures with increased density,” Chen said. “We found extraordinary agreement between theory and experiment for the structures, energies, and compressional behavior. Though some of this behavior had been noted earlier, the agreement between the new highly accurate experimental results and theory really was quite remarkable.”

The team’s results show that superconductivity in this simple element is caused by phonons, or collective vibrations in the crystal structures that germanium assumes under pressure.

The article can be found at: Chen XJ et al. (2011) β-tin→Imma→sh Phase Transitions of Germanium.

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Source: Carnegie Institution.
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