ELASTIC MODULI OF PURE AND GADOLINIUM-DOPED CERIA CERAMICS

Cerium oxide (CeO₂) ceramics currently find application in a variety of modern technologies, including: as automobile exhaust catalysts, as oxygen storage materials and as oxygen ion conductors in solid oxide fuel cells (SOFCs). Recently, reduced and gadolinium-doped ceria were also shown to exhibit a large non-classical electrostriction effect.

The bulk modulus of ceria has been studied experimentally and theoretically during the past four decades but the discrepancy among the results obtained by the various research groups is large. Most of the values measured for both pure and Gd⁺³-doped ceria, cluster around 210 GPa; however, they span from 171 to 357 GPa, independent of Gd⁺³-content. Since ceria is used so widely in industry and its bulk modulus is a State Function, improved accuracy is obviously required.

In the current study, pure cerium oxide and gadolinium doped ceria were synthesized as nanometric powders and sintered at low temperature (~1200 °C) by a two-step process yielding high-density (96-99%) samples. The shear and bulk moduli measured using an ultrasonic method and corrected for porosity demonstrate for the first time that there is a subtle but clear linear decrease with increasing Gd⁺³- content in the composition range CeO₂-Ce_0.8 Gd_0.2O_1.9.