Enhancing micro-electromechanical and tuning optical properties in Nd-doped BIT thin film

Bi₄Ti₃O12 (BIT) and Bi3.25Nd0.75Ti₃O12 (BNT) thin films were deposited on Pt/Ti/SiO₂/Si (100) substrates using pulsed laser deposition. The surface morphologies, ferroelectric domain structures and polarization switching were investigated by atomic force microscopy (AFM) and piezoelectric force microscopy (PFM). The phase and amplitude images of PFM show that the BIT and BNT thin films have clear domain structures. Comparison of the surface morphologies and domain structures indicates that the grain boundaries limit the shape of domain and affect the domain structure. The micro-electromechanical performance was characterized by the effective piezoelectric coefficient d33,f of the thin films. The result shows that the maximum effective d33,f value (100 pm/V) of BNT thin film is larger than that of BIT thin film (30 pm/V). This can be ascribed to BNT thin film with a preferred growth direction of a-axis, resulting in effective enhancement of d33,f. Besides, all the thin films exhibit good optical transmittance in the range of 500-800 nm and the optical band gaps increase from 3.43 eV to 3.52 eV due to Nd doping.