Tougher than diamond

Using a combination of barium titanate and tin, University of Wisconsin-Madison researchers have made the first known material that's stiffer than diamond.

Aside from its value as a gemstone, diamond has the highest thermal conductivity and is the stiffest, hardest material on Earth. Yet despite its benefits, diamond is too expensive to consider in such structural applications as bridges, buildings or airplanes.

While diamond achieves its stability via dense, directional, extremely tight atomic bonds, the UW-Madison researchers created their stiff composite from ordinary materials held together in an extraordinary way, said Roderic Lakes, a professor of engineering physics. ‘We're using a material now that's chosen for having the ability to change volume during phase transformation,’ he said. ‘The material we chose-barium titanate-goes from one solid to another solid.’

Barium titanate is a well researched crystalline material previously used in such applications as microphones or cell phone speakers. Embed bits of it in a tin matrix, and the phase transformation, or shift in the arrangement of atoms, is held back, creating stored energy. ‘Imagine water getting into cracks in the road and freezing,’ said Lakes. ‘It can't expand because it's held in place.’