Never-before-seen "black nitrogen" plugs puzzle in periodic table
Researchers at the University of Bayreuth have created a form of nitrogen that’s never been seen before. Nicknamed “black nitrogen,” the new substance is crystalline, occurs in two-dimensional sheets, and could one day be useful in advanced electronics.
Strangely enough, the idea that black nitrogen didn’t exist has long been considered a mystery. The periodic table is arranged in recurring “periods” where each column is made up of elements with similar properties. Those at the top have the fewest protons and the lowest weight, and each successive element in the group gains protons and weight.
Under high pressure, elements on the top of a column usually take on structures similar to elements further down the group. These different forms are known as allotropes. Ozone is an allotrope of oxygen, for example, while graphite and diamond are both allotropes of carbon.
But nitrogen only has one allotrope – dinitrogen – and doesn’t have any that resemble heavier elements in its group. This was always considered a bit weird, but now a new study has found a previously-unknown allotrope that shows that nitrogen isn’t an exception to the rule, as has long been believed.
To create the new form, the team exposed nitrogen to extreme heat and pressure. It was pressed together between two diamonds to 1.4 million atmospheres of pressure, and over 4,000 °C (7,232 °F). Under those extreme conditions, the nitrogen took on a structure that had never been seen before – but which still looked familiar.
When imaged using X-rays, the nitrogen atoms formed crystalline two-dimensional layers, cross-linked in a zigzag pattern. It appears to have good conductivity, much like that of graphene, which could make it useful in future electronic devices.
Because of its similarities to black phosphorus – an allotrope of the related element phosphorus – the team has taken to calling the new material “black nitrogen.”
"We were surprised and intrigued by the measurement data suddenly providing us with a structure characteristic of black phosphorus,” says Dominique Laniel, lead author of the study. “Further experiments and calculations have since confirmed this finding. This means there is no doubt about it: nitrogen is, in fact, not an exceptional element, but follows the same golden rule of the periodic table as carbon and oxygen do.”
As much potential as black nitrogen might have for electronics, don’t expect to find it in your smartphone anytime soon. Not only is it difficult to produce due to those aforementioned extreme conditions, but the material itself remains unstable and it quickly dissolves when the heat and pressure are relaxed.
"Because of this instability, industrial applications are currently not feasible," says Laniel. “Nevertheless, nitrogen remains a highly interesting element in materials research. Our study shows by way of example that high pressures and temperatures can produce material structures and properties that researchers previously did not know existed.”
The research was published in the journal Physical Review Letters.
Source: University of Bayreuth
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