Newly discovered compound is utilized in superconducting wires and thin films

Less than six months after the metallic compound magnesium diboride was found to be a superconductor (April p11), scientists in the US have developed a practical technique for making wires from it. Other researchers have also produced thin films of the compound and have markedly increased the amount of electrical current that it can carry.

In January, researchers in Japan announced their discovery that magnesium diboride can act as a superconductor (a material in which electricity flows with virtually no resistance) at temperatures of less than -234 °C (39K). Magnesium diboride has been a known substance since the 1950s, but it had never been tested for superconductivity.

To make the wires, scientists at Agere Systems in Murray Hill, New Jersey, filled iron tubes with magnesium diboride powder before stretching and flattening the tubes into ribbons approximately 1 cm wide and 1 m long. The wires were then baked at 870 °C, which fused the magnesium diboride powder into a solid.

The technique is similar to that used to make wires out of high-temperature superconductors. Superconducting wires could find uses in power transmission cables, efficient electric motors and magnets for magnetic resonance imaging machines.

Meanwhile, other scientists have looked into ways of improving the compound's remarkable magnetic properties. Specialists at Imperial College in London blasted magnesium diboride with protons, knocking some of the superconductor's atoms out of place. Researchers at the universities of Wisconsin and Princeton diffused oxygen into thin films of magnesium diboride. The oxygen atoms, they believe, displaced some of the boron atoms in magnesium diboride.

Such defects pin down the magnetic fields penetrating a superconductor. Otherwise, forces generated by the electric current push the magnetic fields into the superconductor's atoms. This jostling dissipates energy, just as electrons bumping into atoms in ordinary metals produce electrical resistance.

To produce their thin films, the Wisconsin and Princeton researchers used ultraviolet lasers to vaporize magnesium diboride, which then settled in a layer a fraction of a micron thick. The oxygen-tainted magnesium diboride films were able to work in magnetic fields almost twice as strong as those lacking the oxygen impurities. Thin superconducting films could be used for electronic components and sensitive magnetic sensors. Nature