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Pressure Turns Nitrogen Gas into Solid Semiconductors

A new kind of nitrogen is what researchers at the Carnegie Institution of Washington have created by applying immense pressure to ordinary nitrogen gas. Their findings are published in this week's issue of Nature.

Nitrogen gas (N2) is abundant on earth, making up about 75 percent of the planet's atmosphere. The triple bond between the two nitrogen atoms makes the gas a very stable compound. At low pressure and temperature, nitrogen forms molecular crystals and becomes an electric insulator. But scientists predicted that by raising the pressure on these crystals to 50 to 94 gigapascals, the nitrogen molecules could be transformed into monoatomic metallic solids. (One gigapascal is roughly 10,000 times the atmospheric pressure experienced at sea level.)

The researchers not only managed to create such solid nitrogen but also found that, unlike its molecular crystal predecessor, the nitrogen becomes a semiconductor in this state. Moreover, they managed to keep the nitrogen in solid form after lowering the pressure back down to normal levels (at temperatures below 100K). "The fact that the major portion of the air has been turned into a semiconducting solid and brought back to be stable at ambient pressure is an important breakthrough for us," team leader Russell Hemley says.

The results of this study confirmed theories that were used to predict new properties, such as high-temperature superconductivity in metallic hydrogen. The researchers initially wanted to convert hydrogen in this manner and they hope to eventually do so.

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