Oxygen defective cerium oxide CeO_2-delta exhibits a non-classical giant electromechanical response that is superior to that of lead-based electrostrictors. The main principle of such response is governed by the re-orientation of cerium-oxygen vacancy pairs in the host lattice. 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 a high coefficient (M₃₃), up to 10^-17 m²/v² , with strongly time-dependent effects. In contrast, we observe no time-dependent effects when the interaction becomes strong (0.6 eV).