Ongoing Projects

• Philipp Gollé-Leidreiter, Bernhard Durschang, Ute Kolb, Hans-Joachim Kleebe

Glass ceramics are a widely spread class of materials, whose potential uses range from optical applications as carriers for lasers to construction materials and to the use as bioactive and biocompatible materials as bone substitutes or dental prostheses. Glass ceramics are defined as consisting of a glass phase and one or more crystalline phases, with the latter primarily determining the properties of glass ceramics. It is therefore of great importance to characterize these phases. In the case of nanocrystalline glass ceramics, the traditional methods of investigating these structures like X-ray powder diffraction can fail due to the small size of the nanocrystals. In this case, electron diffraction methods like 3D electron diffraction and scanning precession electron diffraction (SPED) are an alternative, since electrons interact much stronger with matter than X-rays and, therefore, information can be extracted from much smaller volumes.

The main focus of this project is the characterization of metastable phases in glass ceramics, using electron crystallographic methods, and the understanding processes leading to their stabilization. Special attention is given to glass ceramics from the MgO-Al₂O₃-SiO₂ system with good mechanical properties and potential applications as a dental glass ceramics. These glass ceramics contain spinel (MgAl₂O₄), zirconium titanate (ZrTiO₄) and an unknown metastable LaPO₄ polymorph, whose structure was solved using 3D ED. Potential explanations for the stability of this phase are stresses that occur during crystallization and surface effects due to the special microstructure of this glass ceramic.