Influence of the sintering methods on the electrical properties of cerium-doped aluminium nitride ceramics

This article investigates the densification of AlN ceramics through both Gas Pressure Sintering (GPS) and Spark Plasma Sintering (SPS) methods, employing cerium aluminates (CeAlO₃) as sintering aids and comparing their influence to that of the usual cerium oxide (CeO₂). While sintering aids like CeO₂ promote densification, CeAlO₃ exhibited lower reactivity during both SPS and GPS sintering. Chemical reactions between cerium oxide and aluminium oxide primarily involved the reduced phase as cerium sesquioxide (Ce₂O₃). On the basis on the Ce₂O₃–Al₂O₃ pseudo-binary system, the formation of secondary phases, such as CeAlO₃ and CeAl₁₁O₁₈, during sintering was explained and confirmed by XRD. From complementary characterizations, it has been shown that sintering significantly impacted secondary phase composition and distribution. By employing specific densification cycles, SPS yielded smaller grains and thicker secondary phase cordons which led to enhanced electrical conductivity. Conversely, GPS produced coarser microstructures including larger grains and a network of secondary phases and some agglomerations at the triple points. These modifications influenced the overall conductivity. SPSed samples with 3 wt.% CeO₂ and short dwelling times demonstrated higher electrical conductivity, exceeding by about 6 orders of magnitude the electrical conductivity of those obtained by GPS.