Transparent nanocrystalline MgO by rapid and low-temperature spark plasma sintering

We investigated superfast densification of nanocrystalline MgO powders by spark plasma sintering (SPS) between 700 degreesC and 825 degreesC under applied pressures of 100 and 150 MPa. Fully-dense transparent nanocrystalline MgO with a 52-nm average grain size was fabricated at 800 degreesC and 150 MPa for 5 min. In-line transmissions of 40% and 60% were measured compared to MgO single crystal, for the yellow and red wavelengths, respectively. Densification occurs by particles sliding over each other; the nanometric grain size and pores lead to the optical transparency. The light brownish color of the nanocrystalline MgO is due to the oxygen vacancy color centers, originating from the reducing atmosphere of the SPS process.