Charge distribution and lattice ordering in nano-scale granular magnesium aluminate spinel: The role of composition, grain size and applied electric

Seminars
29.11.2018
14:30
David Wang Auditorium, 3rd floor Dalia Maydan Bldg
Mr. Mahdi Halabi, Invited Speaker

Mr. Mahdi Halabi, Invited Speaker

Department of Materials Engineering, Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University

The development of many technologies such as fuel cells, sensors, nuclear reactors, electronic devices and armor windows require ionic oxides whose specific properties were achieved by a nanoscale granular structure. The properties of these materials are predicted to be influenced strongly by both lattice ordering and the formation of a space charge region. It was suggested to study these two interrelated mechanisms using a test-case system of nonstoichiometric nanoscale granular magnesium aluminate spinel (MgO·nAl2O3, MAS). For this aim, the effects of composition (synthesis), grain size (thermal annealing), and applied electric field on the distribution of structural defects and the consequent formation of a space charge region was investigated in detail. 
Thus, we applied a combination of electron energy loss spectroscopy and off-axis electron holography to determine the role of cations and charged defects on the space charge potential in nano-scale MAS grains and particles. 
The experimental results confirm excess Al+3 or Mg+2 cations near interfaces and surfaces of Al-rich or Mg-rich MAS nano-scale grains, respectively. Additionally, the grain core is electrically charged when the grain size is reduced towards the Debye length.  Furthermore, applying an electric field during the annealing of these grains reduces the width of the space charge region and increases lattice order. 
The origin of charge redistribution in nonstoichiometric nanoscale granular MAS and its discharge following the application of an electric field is discussed.

 

Professor Michael S. Silverstein