  Oxygen defective cerium oxides exhibits a non classical giant
electromechanical response that is superior to lead based electrostrictors. In
this work, we report the key role of acceptor dopants, with different size and
valence Mg2+, Sc3+, Gd3+, and La3+, on polycrystalline bulk ceria. Different
dopants tune the electrostrictive properties by changing the electrosteric
dopant defect interactions. We find two distinct electromechanical behaviors
when the interaction is weak dopant vacancy binding energy 0.3 eV,
electrostriction displays high coefficient, up to 10-17 m2V-2, with strongly
time dependent effects. In contrast, we observe no time dependent effects when
the interaction becomes strong 0.6 eV.
