  Lead free, silicon compatible materials showing large electromechanical
responses comparable to, or better than conventional relaxor ferroelectrics,
are desirable for various nanoelectromechanical devices and applications.
Defect-engineered electrostriction has recently been gaining popularity to
obtain enhanced electromechanical responses at sub 100 Hz frequencies. Here, we
report record values of electrostrictive strain coefficients (M31) at
frequencies as large as 5 kHz (1.04 x 10-14 m2 per V2 at 1 kHz, and 3.87 x
10-15 m2 per V2 at 5 kHz) using A-site and oxygen-deficient barium titanate
thin-films, epitaxially integrated onto Si. The effect is robust and retained
even after cycling the devices >5000 times. Our perovskite films are
non-ferroelectric, exhibit a different symmetry compared to stoichiometric
BaTiO3 and are characterized by twin boundaries and nano polar-like regions. We
show that the dielectric relaxation arising from the defect-induced features
correlates very well with the observed giant electrostrictive response. These
films show large coefficient of thermal expansion (2.36 x 10-5/K), which along
with the giant M31 implies a considerable increase in the lattice anharmonicity
induced by the defects. Our work provides a crucial step forward towards
formulating guidelines to engineer large electromechanical responses even at
higher frequencies in lead-free thin films.
