New, intermediate polymorph of CeAlO3 with hexagonal structure – formation and thermal stability

Abstract

This work presents the results of studies on solid state reaction in a highly dispersed CeO₂–Al₂O₃ system under a reducing atmosphere. The formation of a new metastable hexagonal form of CeAlO₃, isomorphous to hexagonal YAlO₃, at 850 °C has been confirmed for the first time by TEM, XRD, FT-IR and measurement of magnetic susceptibility. Above 900 °C, the hexagonal phase transformed into a common tetragonal polymorph. Magnetic susceptibility data indicates that both CeAlO₃ polymorphs contain Ce³⁺ ions, but the unit cell volume per formula unit is noticeably bigger (26%) for the hexagonal polymorph. This may suggest that the hexagonal CeAlO₃ polymorph is stabilized by the interaction with the Al₂O₃ support.