Abstract
Electromechanically active ceramic materials, piezoelectrics and electrostrictors, provide the backbone of a variety of consumer technologies. Gd- and Sm-doped ceria are ion conducting ceramics, finding application in fuel cells, oxygen sensors, and, potentially, as memristor materials. While optimal design of ceria-based devices requires a thorough understanding of their mechanical and electromechanical properties, reports of systematic study of the effect of dopant concentration on the electromechanical behavior of ceria-based ceramics are lacking. Here we report the longitudinal electrostriction strain coefficient (M33) of dense RExCe1–xO2–x/2 (x ≤ 0.25) ceramic pellets, where RE = Gd or Sm, measured under ambient conditions as a function of dopant concentration within the frequency range f = 0.15–350 Hz and electric field amplitude E ≤ 0.5 MV/m. For >100 Hz, all ceramic pellets tested, independent of dopant concentration, exhibit longitudinal electrostriction strain coefficient with magnitude on the order of 10–18 m2/V2. The quasi-static (f < 1 Hz) electrostriction strain coefficient for undoped ceria is comparable in magnitude, while introducing 5 mol % Gd or 5 mol % Sm produces an increase in M33 by up to 2 orders of magnitude. For x ≤ 0.1 (Gd)–0.15 (Sm), the Debye-type relaxation time constant (τ) is in the range 60–300 ms. The inverse relationship between dopant concentration and quasi-static electrostrictive strain parallels the anelasticity and ionic conductivity of Gd- and Sm-doped ceria ceramics, indicating that electrostriction is partially governed by ordering of vacancies and changes in local symmetry.
Highlights
Gd- and Sm-doped ceria are among the most extensively studied examples of solid-state ionic conductors,[1] finding application in fuel cells, sensors,[2] and, potentially, as memristor materials.[3]
Gd-doped ceria (GdDC, a.k.a. cerium gadolinium oxide, CGO) ceramics and thin films, equilibrium solids, exhibit time-dependent elastic moduli; that is, they are anelastic under anisotropic applied stress.[4−7] Gd- and Smdoped ceria (SmDC, a.k.a. cerium samarium oxide, CSO) ceramics and thin films exhibit room temperature, recoverable, mechanical creep under nanoindenter load hold.[8−10] The dependence of Poisson’s ratio on strain magnitude,[11,12] spontaneous volume expansion over time, and hysteresis of the cubic lattice parameter during thermal cycling[5,13] have been reported. These mechanical anomalies have tentatively been ascribed to symmetry-lowering lattice distortions, that is, elastic dipoles created in the vicinity of charge-compensating oxygen vacancies, which, depending on the dopant concentration, can occupy a few percent of the anion sublattice sites.[14−17] We have recently shown[9] that the dominant anelastic behavior of Sm-doped ceria ceramics decreases with dopant concentration (x = 0.05−0.25)
Mechanical properties of Sm- and Gd-doped ceria ceramics have been reported, how the electromechanical behavior, in particular, nonclassical electrostriction, observed to date in Gd-doped ceria,[14,18−21] (Y,Nb)-stabilized δ-Bi2O3,22 and La2Mo2O923 depends on dopant concentration has not been systematically studied
Summary
Gd- and Sm-doped ceria are among the most extensively studied examples of solid-state ionic conductors,[1] finding application in fuel cells, sensors,[2] and, potentially, as memristor materials.[3]. Gd-doped ceria (GdDC, a.k.a. cerium gadolinium oxide, CGO) ceramics and thin films, equilibrium solids, exhibit time-dependent elastic moduli; that is, they are anelastic under anisotropic applied stress.[4−7] Gd- and Smdoped ceria (SmDC, a.k.a. cerium samarium oxide, CSO) ceramics and thin films exhibit room temperature, recoverable, mechanical creep under nanoindenter load hold.[8−10] The dependence of Poisson’s ratio on strain magnitude,[11,12] spontaneous volume expansion over time, and hysteresis of the cubic lattice parameter during thermal cycling[5,13] have been reported These mechanical anomalies have tentatively been ascribed to symmetry-lowering lattice distortions, that is, elastic dipoles created in the vicinity of charge-compensating oxygen vacancies, which, depending on the dopant concentration, can occupy a few percent of the anion sublattice sites.[14−17] We have recently shown[9] that the dominant anelastic behavior of Sm-doped ceria ceramics decreases with dopant concentration (x = 0.05−0.25).
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