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

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 degrees C has been confirmed for the first time by TEM, XRD, FT-IR and measurement of magnetic susceptibility. Above 900 degrees 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.