Nanotomography of transparent alumina ceramics.

Researchers at the Powder Technology Laboratory (http://ltp.epfl.ch/, P. Bowen and M. Stuer) and the Center for Electron Microscopy (http://cime.epfl.ch/, M. Cantoni, Prof. C. Hebert) have made a significant breakthrough in the optical modelling of transparent polycrystalline alumina (PCA) using nanoscale 3D FIB tomography. Production of transparent ceramics, to replace single crystal sapphire, has become a topic of great interest in recent years. Transparent ceramics with the use of near-net shaping lends itself to applications ranging from biomedicine to solar energy.
However, the mechanisms governing ceramic transparency, translucency, and opaqueness were found to be inadequate. Previously used models of both grain boundary and pore scattering have been used without sufficient experimental corroboration. An extensive experimental analysis of transparent alumina samples produced by Spark Plasma Sintering (Z. Zhao, Stockholm University, Sweden). A first direct link between the observed transparency, defect size and porosity, was established using unprecedented experimental full 3D pore reconstruction from the FIB tomography.
The new theoretical model developed in collaboration with C. Pecharroman (Instituto de Ciencia de Materiales de Madrid, CSIC) showed how the previous model was erroneous by an order of magnitude. These exciting experimental and new theoretical results correctly identifies for the first time the relative contributions of different scattering mechanisms. This now paves the way forward for microstructural tuning of transparent polycrystalline alumina for a multitude of applications.

M. Stuer et al. Adv. Func.Mater. DOI: 10.1002/adfm.201200123 (2012)