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

Abstract

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 3wt.% CeO2 and short dwelling times demonstrated higher electrical conductivity, exceeding by about 6 orders of magnitude the electrical conductivity of those obtained by GPS.