Perovskite is a structure type that consists of three different components: alkaline earth metals such as calcium, transition metals such as iron and negative ions, which are often oxygen. Perovskites are usually described as inorganic chameleons as they are very flexible and can exhibit different properties depending on their environment. They are easy to manufacture, and by varying the structure, new interesting functions can be created in the material.
In her recently published PhD thesis at Chalmers Annika Eriksson has studied the link between these new functions and the structure of perovskites. She has, among other things, examined a group of perovskites which have good conductive properties for both oxygen ions and electrons. These properties are sought after as cathode material in fuel cells.
Present-day fuel cells have a working temperature of 800-1,000°C. They therefore have limited areas of use and require a great deal of energy to heat up.
“One aim is to be able to reduce the working temperature to a more manageable level in the range 300-600°C,” says Professor Sten Eriksson, who was the supervisor for the thesis. “We also hope that new perovskites can offer a longer lifespan and better conductive capacity for ions and electrons in fuel cells.”
A supercell structure of an oxygen-deficient perovskite. The supercell structure contains voids, or holes, which make it possible for oxygen ions and/or electrons to move. In doing so, the perovskite can function as a conductor for both ions and electrons.
The fact that perovskites conduct oxygen effectively also means that they can be used in membranes for the separation of oxygen from other gases. An interesting application could be carbon dioxide storage in bedrock, a potentially very important form of technology to slow down climate changes. Before the carbon dioxide is pumped into the bedrock, other gases, including oxygen, must be removed from the gas mixture.
Annika Eriksson has also examined a group of perovskites which are multiferroic materials, also known as multifunctional materials. This means that they are spontaneously polarisable in an electric field and at the same time they have magnetic properties. Materials of this kind are important in nanoelectronics research as they can combine polarised and magnetic effects in one circuit.
The thesis “Interplay between structure and properties in perovskite related materials” was defended on March 6, 2009.