New form of synthetic metastable germanium

Materials World magazine
1 Jan 2007

A synthetic metastable form of germanium has recently been developed that has rare properties with technological potential, say scientists at the University of Houston (UH), USA. Led by Arnold Guloy, Professor of Chemistry, the team from UH and the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany, has revealed that the new element has a crystal habit with a clathrate (open framework) structure decorated with cavities. The material is less dense than its natural analogue and has the unusual property of ice - it floats in its own liquid.

‘It is always scientifically important to find a new form of an element that is not made naturally,' Guloy says. ‘Since the material has never been made before, there is no design or direct application for it yet. The synthesis of this unusual material and the predicted properties open many possibilities.'

According to Guloy, there is much interest in clathrate semiconductors as, due to their porous structures, they have lower densities and larger band gaps than the usual semiconductors. Germanium already has many applications that range from use in fibre optic communication networks to infrared night vision systems. All computerised devices and those that use radio waves exploit its properties. But classical silicon and germanium semiconductors exhibit small and indirect band gaps that are unsuitable for many optoelectronic applications that combine light and electronics technology.‘This new form of germanium should allow for new avenues of research,' says Jon Bear, Dean of UH's College of Natural Sciences and Mathematics.

‘Until our [study], there was no scalable and high yield preparative technique for silicon- and germanium-based clathrate semiconductors,' he explains.‘The breakthrough has resulted in a porous clathrate material that has the potential to emit light, [be] formed at 300°C and, being a solution technique, it can easily be scaled to prepare thin films,' says Guloy. ‘All previously known compounds with a clathrate structure have something in the cages to keep them from collapsing.

This development will provide scientists with information to design high-efficiency thermoelectrics and gain a better understanding of superconductivity in this genre of materials.