The formula for turning cement into a semiconductor

Scientists from the US, Japan, Finland and Germany have developed a formula for turning liquid cement into liquid metal. This makes cement a semiconductor and opens up its use in the consumer electronics marketplace for thin films, protective coatings and computer chips.

“This new material has lots of applications, including as thin-film resistors used in liquid-crystal displays, basically the flat panel computer monitor that you are probably reading this from at the moment,” said Chris Benmore, a physicist from the US Department of Energy’s (DOE) Argonne National Laboratory.

This change demonstrates a unique way to make metallic-glass material, which has positive attributes including better resistance to corrosion than traditional metal, less brittleness than traditional glass, conductivity, low energy loss in magnetic fields, and fluidity for ease of processing and moulding.

Previously, only metals have been able to transition to a metallic-glass form. Cement does this by a process called electron trapping, a phenomena only previously seen in ammonia solutions.

“This phenomenon of trapping electrons and turning liquid cement into liquid metal was found recently, but not explained in detail until now,” Benmore said.

“Now that we know the conditions needed to create trapped electrons in materials we can develop and test other materials to find out if we can make them conduct electricity in this way.”

The scientists studied mayenite and melted it at temperatures of 2000°C and then processed the material in different atmospheres to control the way that oxygen bonds in the resulting glass. This let the liquid cool into a glassy state that can trap electrons in the way needed for electronic conduction. The scientists discovered that the conductivity was created when the free electrons were ‘trapped’ in the cage-like structures that form in the glass. The trapped electrons provided a mechanism for conductivity similar to the mechanism that occurs in metals.

To uncover the details of this process, scientists combined several experimental techniques and analysed them using a supercomputer. They confirmed the ideas in experiments using different X-ray techniques at Spring 8 in Japan combined with earlier measurements at the Intense Pulsed Neutron Source and the Advanced Photon Source.