Boosting memory capacity with Prussian blue

BOOSTING MEMORY CAPACITY WITH PRUSSIAN BLUE

Prussian blue – composed of iron and cyanide – has been prized by artists since the 18th century. Today, scientists are taking a keen interest in this pigment by studying what happens when some of its iron atoms are replaced by cobalt atoms. 
And for good reason, this new compound is able to change colour by switching from one state to another in a stable manner. The two colours and states make it possible to memorize binary information and store computerised data in binary form using the digits “0” and “1”. 
 
Anne Bleuzen, lecturer and chemist (Paris 11 University - CNRS): 
There are two very closely related energy states in these compounds, and it is possible to cause the compound to switch from one state to another by applying an external stimulus, such as light, temperature or pressure. Here, for example, the violet ground state is the “0” state; if we subject it to an external stimulus such as light, for example, we can cause it to switch to the “1” state and the colour changes to brown. 
 
With the help of these Prussian Blue derivatives, chemists hope to be able to store information on the scale of a few atoms and thus substantially reduce the size of hard drives. 
The downside, however, is that the change of state occurs at very low temperatures with Prussian blue: at around -200°C. But in order to use this compound to make miniature hard drives someday, the switching must be operative at room temperature. 
To try to solve this problem, Anne Bleuzen’s team is performing measurements on SOLEIL synchrotron’s AILES beamline, an infrared radiation beamline that can reveal the structure of Prussian blue. 
 
Pascale Roy, manager of the AILES beamline (Synchrotron): 
We have two components and the position of the atoms, and we also have the restoring force between the various atoms. The far-infrared will not only provide information on the position of the atoms, but also on the force that binds the different atoms together. 

Prussian blue derivatives are composed of iron, cobalt and cyanide. They also contain cations – Sodium, in this case – that make the overall structure more or less rigid and switching more or less easy. 
 
Anne Bleuzen: 
The cobalt iron cyanide linkages comprise strong chemical bonds and the alkali cations disrupt these chemical bonds. 
We are interested in the interaction of this cation with the structure and the cobalt iron cyanide linkages. 
 
This knowledge at the atomic scale is an essential step towards finding the right mix of cations so that someday memory drives weighing just a few grams can be manufactured for laptops, mobile phones and MP3 players. It will take a few more years, however, to find manufacturing processes for these extremely small structures.