Electronics - Micro-/Nanotechnology

How Impurities Can Enhance the Properties of Ceramics

Materials scientists at TU Darmstadt are aiming for nothing less than to reinvent ceramic. To this end, they are delving into its atomic structure.

Photo credit: Claus Völker

“The challenge in research is the question, not the answer.” This is the credo of Jürgen Rödel, professor at TU Darmstadt, who seeks to understand the mechanical properties of ceramics. In his opinion, much more can be done with this hard and brittle material beyond the already impressive list of applications, which includes sensors, and capacitors, among many others.

At first glance, Rödel’s approach seems paradoxical: His aim is to improve ceramics by “destroying” the atomic structure, which includes the mechanical deformation of ceramics under controlled pressure and temperature. His team is focusing on dislocations, a type of crystal defect in which atoms in a crystal lattice are out of position in the crystal structure. Dislocations are generated when stress is applied and lends materials with plsatic-like deformation. These defects have been well known in metals, however, their application in hard ceramics has was considered virtually unthinkable until recently.

Crystal defects, such as the absence of an atom in a regularly formed crystal lattice (also referred to as point defects), have been well researched and lend beneficial properties to materials, such as increasing the conductivity of semiconductors. In some cases, the defect can take the form of a straight line through the crystal lattice. While a promising means of tuning materials properties, controlled, one-dimensional defects in ceramics have remained relatively untouched, Prof. Rödel says.

What makes dislocations in ceramics interesting is their ability to serve as channels for transmitting charge and increasing conductivity. Rödel and his team hope to use their innovative design to increase the efficiency of fuel cells as “at the end of the dislocations, namely on the surface of the crystal, oxygen can be incorporated or removed.”

As ceramics retard the propagation of heat, they are well-suited for use as thermoelectric elements—materials that convert waste heat into electricity. Furthermore, dislocations remain stable up to 500°C, whereas point defects fall apart at around 100°C.

One of the current challenges the team is facing is to find the optimum temperature, electrical potential, and other parameters for the mechanical deformation. But Rödel and his group are already making progress and the first partners in his network are working on dislocation-based photovoltaic systems in England and on high-resolution electron microscopy in Japan.

All in all, it appears that Rödel has found the right question and is getting ever closer to the answer.

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