Piezoelectric Properties of {100}-Oriented Epitaxial BiCoO3-BiFeO3 Films Measured Using Synchrotron X-ray Diffraction

Electric polarization and the strain of {100}-oriented epitaxial BiFeO₃ and BiFeO₃-BiCoO₃ films grown on (100)_cSrRuO₃ ∥ (100)SrTiO₃ substrates were simultaneously measured using synchrotron X-ray diffraction. The apparent piezoelectric coefficient d_33,obs values of BiFeO₃ and BiFeO₃-BiCoO₃ films were 28 and 63 pm/V, while the observed electrostrictive coefficient Q_11,obs values of the films calculated from electric polarization and strain were 1.4 ×10^-2 and 3.6 ×10^-2 m⁴/C², respectively. These results implied that the films become soft by the addition of BiCoO₃ into BiFeO₃.