Sm-doped ceria, Ce1-xSmxO2-x/2 (SmDC), is one of the most studied oxygen ion conductors, however, its elastic properties received relatively little attention. At x > 30% oxygen vacancies, SmDC undergoes ordering, leading to a... [ view full abstract ]
Sm-doped ceria, Ce1-xSmxO2-x/2 (SmDC), is one of the most studied oxygen ion conductors, however, its elastic properties received relatively little attention. At x > 30% oxygen vacancies, SmDC undergoes ordering, leading to a phase transition from a fluorite to a double fluorite phase. We have investigated electrostriction coefficient, unrelaxed and relaxed elastic moduli of SmxCe2-xO2 polycrystalline ceramics in both phases: 5% < x < 55%.
In the fluorite phase, SmDC exhibits a non-classical electrostriction effect, which gradually decreases from M33 » 1016 m2/V2 to M33 » 10-18 m2/V2 at x > 25%. These values are much larger than those expected from the Newham’s scaling law (classical electrostriction).
According to ultrasonic pulse-echo technique (which after correction for porosity, provides accuracy in the elastic moduli better than ±0.5%), the shear, Young’s and bulk moduli show linear decrease with the composition in both phases. However, the rate of the decrease within the fluorite phase is higher for Young’s and shear moduli, while the bulk modulus decrease rate remains the same in both phases.
The nanoindentation measurements show that SmDC exhibits room temperature mechanical creep, indicating that SmDC is anelastic, which is similar to Gd-doped ceria. The creep rate in the fluorite phase is much larger than in the double fluorite phase and within the fluorite phase, it decreases with Sm content.
Our findings indicate that elastic properties and electrostriction in SmDC are strongly affected by the vacancy concentration, in general, and by vacancy ordering in particular. The difference in the behavior of the fluorite and the double fluorite phases indicates that mobility of the vacancies in the fluorite phase is the factor affecting elastic, anelastic and electrostrictive properties.
