Related mechanism of transparency in MgAl₂O₄ nano-ceramics prepared by sintering under high pressure and low temperature

We fabricate transparent MgAl₂O₄ nano-ceramics, which are composed of 40 nm grains, by sintering under high pressure and low temperatures. Analysis of the grain size, differential strains, yield strength and porosity obtained from transmission electron microscopy and x-ray diffraction indicates that the pores at the grain boundary triple junctions can retard grain boundary migration and thus prevent grain growth. It is found that the relatively high density for MgAl₂O₄ nano-ceramics produced at low-temperature and high pressure is attributed mainly to the large energy in the grain exteriors. The decrease in the transparency with increasing temperature (>700 °C) is therefore a result of the light scattering at large pores. On the basis of these results, we propose a mechanism of transparency in MgAl₂O₄ nano-ceramics.