Microwave dielectric properties of nanocrystalline TiO 2 prepared using spark plasma sintering

Abstract

TiO 2 bulk ceramics were fabricated by using both spark plasma sintering (SPS) and the conventional sintering method (CSM). Starting materials were ultra fine rutile powders (<50 nm) prepared via the sol–gel process. CSM achieved the relative sintering density of 99.2% at 1300 °C. The grain size of 1300 °C sintered specimen was 6.5 μm. However, the sintering temperature of SPS for the density of 99.1% was as low as 760 °C, where the grain size was only 300 nm. In order to re-oxidize the Ti 3+ ions due to the reducing atmosphere of the SPS process and the high temperature of the CSM process, the prepared TiO 2 specimens were annealed in an oxygen atmosphere. The dielectric constant ( ɛ r) and quality factor ( Q × f) of SPS-TiO 2 re-oxidized specimens in a microwave regime were 112.6 and 26,000, respectively. These properties were comparable to those of 1300 °C sintered CSM specimens ( ɛ r ∼ 101.3, Q × f ∼ 41,600). These microwave dielectric properties of nanocrystalline TiO 2 specimens prepared using SPS were discussed in terms of grain size variation and Ti 4+ reduction.