Broadband dielectric characterization of TiO2 ceramics sintered through microwave and conventional processes

In this work the microwave sintering (MW) of pure submicron rutile TiO2 powder has been conducted in complete electric field using a single mode cavity of 2.45 GHz and without any susceptor. The sintering conditions were varied and similar sintering cycles were also done using a conventional furnace (CV), in carefully measuring the temperature in both processes. The dielectric properties, from kHz to GHz were determined and a comparison analysis was made between microwaved and conventional sintered specimens. It is shown that microwave sintering allows to obtain dense material (>95%) in a very short time (10–15 min) at a sintering temperature ranging from 1000 °C to 1300 °C. Some samples are fully dense (>99% theoretical density) after being microwave heated for ∼10 min at ∼1300 °C. Using the microwave heating, the processing temperature to get high dense material (i.e. >94%) is lowered by ∼150–175 °C compared to conventionally sintered samples. It is also shown that an annealing in air at ∼800 °C for ∼4 h, leads to very low loss TiO2 ceramic in the entire frequency range investigated. Owing to the lowest sintering temperature provided by microwaves, the low frequency dielectric losses are smaller for MW samples than for CV sintered samples. Among the highest reported microwave Q factors (∼7350) have been measured on pure TiO2 samples exhibiting the largest grain size (∼1.5 μm) and density (>96%).