1. DST/NRF Centre of Excellence in Strong Materials, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, Private Bag 3, Johannesburg 2050, South Africa
2. DST/NRF Centre of Excellence in Strong Materials and School of Physics, University of the Witwatersrand, Johannesburg, Private Bag 3, Johannesburg 2050, South Africa
3. Fraunhofer Institute for Ceramic Technologies and Systems, Winterbergstra_e 28, 01277 Dresden, Germany