A germanium crystal (top); metallic glasses are ideal for making golf clubs and tennis racquets

Legendary US golfer Tiger Woods may not know Srikanth Sastry. The same may be true of reigning tennis queen Maria Sharapova. But in future, the chances of such players winning big events might just depend on the number crunching Sastry does in the Jawaharlal Nehru Centre for Advanced Scientific Research in Jakkur near Bangalore.

Computer simulations that Sastry did together with Austen Angell at the Arizona State University in the US have led to the creation of the world’s first metallic glass from a single metal — germanium. The work, reported in Nature, shatters the myth that a pure metal cannot be “supercooled” to form glass.

The metallic glass that the scientists at Angell’s lab, including Indian researcher Harish Bhat, developed from liquid germanium may not have any significant direct applications, but the knowledge they gained would help tweak better a class of new materials — called bulk metallic glasses — that came into existence in the early 1990s.

Often regarded as the third revolution in materials after the inventions of steel and plastic, bulk metallic glasses are used in making premium golf clubs, tennis racquets and baseball bats. These high-quality engineering materials have critical applications in medical, defence and aerospace industries as well. The new finding will help produce materials of even better quality.

There are many reasons why metallic glass — prepared in bulk in 1993 by California Institute of Technology scientist Bill Johnson — is a darling of materials scientists. Concocted from a blend of several elements — the major ones being zirconium and titanium — metallic glasses are elastic, strong and corrosion-proof. Despite this strength, it is delicate, having the propensity to shatter like glass.

“There is, however, one problem. All bulk metallic glasses are perfected through trial-and-error methods with the scientists having no insight into what each component brings to the table,” says U. Ramamurty, a materials scientist at Indian Institute of Science, Bangalore. “This is because in glass, unlike metals, there is no structure to see,” he explains.

Glasses are made by cooling a liquid with the prerequisite that no crystallisation occurs during the process. This is true of the common glass we use to make windowpanes and bottles as well as of metallic glasses.

But the new metallic glass at Angell’s lab, being created from a single element, offers the possibility of studying its characteristics closely. “This would help us one day to produce better bulk metallic glasses,” says Ramamurty, who plans to collaborate with the team for furthering the work. “After all, good engineering requires good science,” he says.

Sastry and Angel hit upon the idea when they were studying a novel phase transition in silicon. Using simulations, they tested the strength of silicon crystal structures so that they could “supercool” the liquid silicon without crystallising it. Supercooling is a process by which molten metals are cooled below their melting point without losing their liquid structure.

However, their initial attempts failed in turning silicon and germanium into glasses. But, says Sastry, “we knew from our simulation studies that the good glass-former (liquid that can form glass) would fall between germanium and tin” — two metals that fall in the same group as silicon on the periodic table of elements. To make germanium acquire attributes of this “ideal glass-former” they thought of applying pressure.

“It really worked,” explains Sastry. Materials such as water, silicon and germanium have an unusual thermodynamic behaviour: they expand as they switch from the liquid state to a solid one. This gives rise to a unique property: when pressure is applied, the melting temperatures come down drastically.

The application of high pressure not only helped germanium to remain liquid while being rapidly cooled, but also broke down its signature tetrahedral (four-cornered) crystalline structure. Foregoing crystallisation, after all, is the major condition for glass formation.