  Recent discovery of giant electrostriction in rare earth (RE (III))
substituted ceria (CeO2) thin films driven by electroactive defect complexes
and their coordinated elastic response, expands the material spectrum for
electrostrain applications beyond the conventional piezoelectric materials.
Especially Gd substituted CeO2, with Gd concentration >10% seems to be an ideal
material to obtain such large electrostrain response. However, there are not
many experimental studies that systematically investigate the effect of RE
(III) ion-defect interaction and RE concentration on electrostriction. Here we
perform structure-property correlation studies in bulk ceramics of RE3+
substituted ceria doped with RE=Y, La and Gd at various concentrations upto a
maximum of 20%, to understand the features responsible for giant
electrostriction. Our results show that Y substituted ceria, with atleast 20% Y
substitution, is clearly both a giant M and a Q electrostrictor at low
frequencies (<20 Hz), and this correlates with the unique attractive
defect-dopant interaction of Y with oxygen vacancies. La has a repulsive
interaction with oxygen vacancies, and La doped ceria at all the studied
compositions (upto 20%) does not show giant electrostiction. Gd has a neutral
interaction, and only 20% Gd doped ceria at best falls at the border of
classification between giant and non-giant electrostrictors at frequencies
<0.05 Hz. Our work takes a step back from thin-films and assesses the
fundamental defect features required in the design of giant electrostrictors.
