Mechanical and electromechanical properties of acceptor doped BaZrO3

Electrostriction is the second order (quadratic) electromechanical response and describes electric-field induced strain that is proportional to the square of the electric field. Commercial electrostrictors have high dielectric... [ view full abstract ]

Electrostriction is the second order (quadratic) electromechanical response and describes electric-field induced strain that is proportional to the square of the electric field. Commercial electrostrictors have high dielectric constants (>3000) and electrostriction coefficients of M₃₃ > 10^-16 m²/V². Recently, we have reported electrostriction coefficients of ~0.5∙10^-17 to ~2∙10^-16 m²/V² for two groups of fluorite-structured ceramics with high concentration of oxygen vacancies and low dielectric constant: (Y,Nb)-stabilized δ-Bi₂O₃  and Gd doped CeO₂. These coefficients do not follow the well-known empirical Newnham relationship, hence are considered non-classical. Further studies on Gd doped CeO₂ showed that the strain can be attributed to a field-induced rearrangement of local lattice distortions associated with oxygen vacancies.

The acceptor-doped perovskite Ba(Zr,Y)O₃ has a large concentration of oxygen vacancies in dry state, and may absorb water forming mobile protonic interstitials. We have measured the electrostriction of partially hydrated Ba(Zr,Y)O₃ and found an exceptionally high coefficient of (1-9)∙10^-16 m²/V². The electromechanical response shows relaxation with a characteristic frequency of ~100 Hz. The relaxation frequency increases upon hydration. DFT studies show that vacancies and protonic interstitials cause local lattice distortions and form local dipole moments that could interact with the electric field causing the abnormal strains. The elastic moduli decrease with increasing dopant concentration in both, dry and hydrated state. Hydration decreases the elastic moduli, even though it fills the oxygen vacancies.

With these findings, the previously reported class of non-classical electrostrictors can be expanded to include perovskite acceptor doped Ba(Zr,Y)O₃.