Charge distribution in magnesium aluminate spinel (MAS) results in the formation of a space-charge region that plays a critical role in assigning functional properties. Explanation of this phenomenon are reported though quantitative experimental evidence for nano-scale granular MAS is indirect[1,2]. In this talk, the effect of composition, grain size and applied electric field on the space-charge potential in nanoscale MAS is presented.
The electrostatic potential distribution in nonstoichiometric grains was measured by off-axis electron holography and compared to the distribution of cations and defects as measured by electron energy loss spectroscopy.
We demonstrated quantitatively that regardless of grain size, excess Mg+2 or Al+3 cations resides in the vicinity of grain-boundaries of Mg- and Al-rich MAS, respectively. Such variations in cation and defect distribution should enable to calculate the space-charge-potential (SCP). However, the wide range of reported values for defect formation energies (0.82-8.78eV) prevents estimating the SCP. Consequently, we applied electron holography to measure directly the SCP. Furthermore, by applying a moderate electric field (~150 V/cm) during thermal annealing, structural ordering was observed.
[1] Halabi, M., Ezersky, V., Kohn, A. and Hayun, S. (2016), Charge Distribution in Nano-Scale Grains of Magnesium Aluminate Spinel. J. Am. Ceram. Soc. doi:10.1111/jace.14610.
[2] Rubat du Merac, H. Kleebe, M. M. Müller and I. E. Reimanis, `Fifty Years of Research and Development Coming to Fruition; Unraveling the Complex Interactions during Processing of Transparent Magnesium Aluminate (MgAl2O4) Spinel,` J Am Ceram Soc, 96[11] 3341-3365 (2013).
