Enhanced Piezoelectric Response in Orientation-Controlled BiFe_1–xGa_xO₃ Thin Films with Polarization Rotation

The crystal structures and piezoelectric properties of gallium-substituted BiFeO3 (BiFe1–xGaxO3) thin films on (110) LaAlO3 substrates were investigated. The structure of BiFe1–xGaxO3 thin films was found to change from rhombohedral (x = 0) to a (101)-oriented monoclinic phase with a giant c/a ratio (x = 0.40) through two phase coexistence compositions (x = 0.10, 0.20) as the Ga content was increased. The piezoelectric response of the (101)-oriented monoclinic BiFe1–xGaxO3 thin film with x = 0.40 was 1.6 times that of a corresponding (001)-oriented one. Such behavior is unique to the monoclinic phase where polarization can rotate and can be attributed to the fact that the a- and b-axes are more sensitive to polarization rotation than the c-axis.