Stable self-polarization in lead-free Bi(Fe0.93Mn0.05Ti0.02)O-3 thick films

The BiFeO3-based film is one of the most promising candidates for lead-free piezoelectric film devices. In this work, the 1 mu m-thick Bi(Fe0.93Mn0.05Ti0.02)O-3 (BFMT) films are grown on the ITO/glass substrate using a sol-gel method combined with spin-coating and layer-by-layer annealing technique. These films display a large saturated polarization of 95 mu C/cm(2), and a remanent polarization of 70 mu C/cm(2). Especially, the films are self-poled caused by an internal bias field, giving rise to asymmetric polarization-electric field (P - E) loops with a positive shift along the x-axis. A stable self-polarization state is maintained during the applied electric field increasing to 1500 kV/cm and then decreasing back. The weak dependence of P - E loops on frequency (1-50 kHz) and temperature (25-125?) indicate that the internal bias field can be stable within a certain frequency and temperature range. These results demonstrate that the self-polarized BFMT thick films can be integrated into devices without any poling process, with promising applications in micro-electro-mechanical systems.