Electric Field‐Assisted Sintering and Hot Pressing of Semiconductive Zinc Oxide: A Comparative Study

This study aims at comparing hot pressing (HP) and the electric field‐assisted sintering (FAST, also known as spark plasma sintering, SPS) of zinc oxide. Two semiconductive nano‐ and submicrometer powders were investigated, with a particle size of 20–30 and 90–200 nm, respectively. Processing parameters were kept as identical as possible for both sintering methods: sample geometry, heating schedule (however affected by the temperature measurement method), applied pressure, and atmosphere. FAST and HP samples densify by grain‐boundary diffusion. Zinc oxide is nevertheless very sensitive to transient overheating occurring in FAST with pyrometer temperature control, leading to different densification curves. The sintering trajectory reveals that grain size also depends on the temperature history. The electrical conductivity of ZnO dramatically increases at the sintering temperature, but not enough to affect significantly the densification behavior. Ex situ conductivity measurements do not reveal any difference between FAST and HP samples.