Classical electrostriction, describing a second‐order electromechanical response of insulating solids, scales with elastic compliance, S, and inversely with dielectric susceptibility, ε. This behavior, first noted 20 years ago by Robert Newnham, is shown to apply to a wide range of electrostrictors including polymers, glasses, crystalline linear dielectrics, and relaxor ferroelectrics. Electrostriction in fluorite ceramics of (Y, Nb)‐stabilized δ‐Bi2O3 is examined with 16%–23% vacant oxygen sites. Given the values of compliance and dielectric susceptibility, the electrostriction coefficients are orders of magnitude larger than those expected from Newnham's scaling law. In ambient temperature nanoindentation measurements, (Y, Nb)‐stabilized δ‐Bi2O3 displays primary creep. These findings, which are strikingly similar to those reported for Gd‐doped ceria, support the suggestion that ion conducting ceramics with the fluorite structure, a large concentration of anion vacancies and anelastic behavior, may constitute a previously unknown class of electrostrictors.
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.
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