Dopant Concentration Controls Quasi-Static Electrostrictive Strain Response of Ceria Ceramics

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 ( M 33 ) of dense RE x Ce 1– x O 2– 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 m 2 /V 2 . 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 M 33 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.

Electromechanical dopant–defect interaction in acceptor-doped ceria

“…These properties are also investigated in bulk ceria and other oxygen defective fluorites (Bi2O3−δ), illustrating similar outcomes. 9,10,11,12,13,14 The atomistic origin of this uncommon behavior is associated with the presence of charge compensating oxygen vacancies (V O •• ) in the ceria lattice. 15,16 The…”

Trivalent Dopant Size Influences Electrostrictive Strain in Ceria Solid Solutions

“…Within the frequency range examined (0.150 mHz to 130 Hz), the longitudinal electrostriction strain coefficient for all ceramic samples ( M 33 ) is consistently ≥10 2 -fold larger than the value estimated on the basis of the classical scaling law, that is, ≈10 –20 m 2 /V 2 . 9 , 20 , 28 , 30 All samples exhibit some reduction of electrostrictive strain with frequency: ceramics containing Er, Gd, Sm, and Nd display Debye-type strain relaxation above ∼1 Hz, while Lu and Yb are considerably less sensitive to the increase in electric field frequency. In fact, the dependence of the averaged low-frequency electrostriction coefficients, M 33 <1Hz , on the dopant crystal radius is opposite to that of the averaged high frequency electrostriction coefficients, M 33 >100Hz .…”

Non‐Classical Electrostriction in Hydrated Acceptor Doped BaZrO3: Proton Trapping and Dopant Size Effect

“…This is similar to the observations reported for Gd-and Sm-doped ceria. [6,11,30] Even though M | | is similar for the hydrated and the nominally dry samples except for the case of Al.…”

“…The relaxation frequencies of 0.3-2 Hz observed for dry samples (Figure 3b) are similar to that of oxygen vacancies in a fluorite structure. [6,11,30] The nominally dry samples have a very weak dependence of f r on ionic radii in the line Ga 3+ , Sc 3+ , In 3+ and Y 3+ , with less than a decade between the highest (Y 3+ ) and the lowest (Sc 3+ ) sample. In the hydrated samples, the f r increases by about three orders of magnitude in the line Ga 3+ , Sc 3+ , In 3+ and Y 3+ , which clearly indicates that the OH O .…”

“…[ 10 ] An external electric field causes these dipoles to reorient, leading to local and macroscopic strain. According to this “host‐guest” hypothesis of non‐classical electrostriction, [ 2–6,11 ] the dielectric (ε < 80) and the elastic ( S < 10 11 Pa −1 ) properties are largely defined by the host, whilst the electrostriction originates from the guest‐induced (defect‐induced) elastic dipoles. While this hypothesis is still under development, the fact that both doped ceria and (Y,Nb)‐stabilized bismuth oxide are strongly anelastic, clearly proves that these materials contain elastic dipoles.…”