Two breakthroughs in material science, both related to manipulating the arrangement of atoms in a material, were reported recently.
The first is the discovery of a new way of changing the phase of a material, from crystalline to amorphous, using an electrical pulse, which has the potential to revolutionise data storage in gadgets, mainly computer RAM. This new method consumes “a billion times less electricity” than the traditional melt-quench process, according to a paper published in Nature by researchers of IISc-Bengaluru, University of Pennsylvania School of Engineering and Applied Science, and Massachusetts Institute of Technology (MIT).
Electronic storage devices use a type of glass called chalcogenide, which can change its phase from crystalline to amorphous (and back, when needed). In a solid, the atoms are in an ordered state. In an amorphous phase, the atoms are disordered, as in a liquid, but frozen into solid state — sort of a ‘liquid in solid form’. These two phases of a material are used to attribute the values ‘0’ and ‘1’ for storing data. The phase change from crystalline to amorphous is achieved by highly localised application of laser pulses, which consumes a lot of electricity. The crystals must be heated beyond 800 degrees C and then rapidly cooled. If there is a way to convert crystal directly to glass without the intermediate liquid phase, then the power required for memory storage can be greatly reduced.
A group of 12 researchers have demonstrated amorphisation of indium selenide using pulsed electric current. The localised electric pulse causes the weakly bonded layers of the material to slide over each other, like tectonic plates — and, like the plates, they too generate a shock wave, explains one of the researchers, Dr Pavan Nukala of the Centre for Nanoscience and Engineering, IISc, Bengaluru. The wave propagates through the material and causes amorphisation.
This new process has immediate application in microelectronics, but is really a breakthrough in material science as it shows a new way of thinking about amorphisation, he tells Quantum.
Desired misfit
The second discovery — by a team led by Prof Kanishka Biswas, New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru — has led to the synthesis of a new material with high potential for conversion of waste heat into electricity. The group researched into ferecrystals, a class of ‘misfit layered compounds’ (MLC) — so called because their atomic layers are misaligned, like an uneven stack of cards.
MLCs have an interesting property — they do not allow the smooth conduction of heat and thereby block heat transfers. This ultra-low thermal conductivity creates a heat gradient across the material. According to the ‘Seebeck effect’, discovered in 1821, wherever there is a heat gradient, the material can also generate electricity.
The ferecrystal material shows a ‘thermoelectric figure of merit’ of 2.3, a high number that means the material can convert a lot of heat into electricity.
“The material is already generating electricity in the lab. However, it needs to be scaled up for practical use,” Biswas says.
