Comparison of hot pressing and spark plasma sintering in the densification behavior of indium tin oxide‐borosilicate glass composites

Abstract The goal of this study was to fabricate borosilicate glass matrix composites with high optical transmittance and high conductivity by forming percolated segregated networks of indium tin oxide ( ITO ) in the microstructure. ITO nanoparticles and borosilicate glass microspheres were mechanically mixed with ITO concentrations varying from 0 to 2.99 vol%. The mixes were then consolidated using either hot pressing ( HP ) or spark plasma sintering ( SPS ). The effects of changing sintering methods, along with varying other processing parameters such as heating rate, maximum temperature, and applied pressure, had surprising and unanticipated effects. Ac impedance spectroscopy ( IS ), SEM , and EDS results indicated the successful formation of a grain‐like microstructure of the sintered glass using both HP and SPS processing, with the ITO particles segregated to the boundary regions in all samples. IS results indicated percolation threshold values between 0.154 and 0.307 vol% ITO in the HP samples and between 0.307 and 0.764 vol% ITO in the SPS samples, with resistivities as low as 29 (Ω·cm) at 2.99 vol% ITO . Optical properties were dominated by impurities and light scattering at defects such as pores. Contrary to conventional belief, it was found that samples made using SPS required far higher temperatures to fully densify, with all other processing conditions being the same, compared with HP . This behavior was confirmed through repeat tests using different SPS equipment and a wide range of processing conditions.