The ferroelectricity of Bi0.9Pb0.1FeO3 films grown on atomic flat SrRuO3/SrTiO3 substrates

Bi0.9Pb0.1FeO3 (BPFO) films were grown on SrRuO3 (SRO)/SrTiO3 (STO) substrates. The surface morphology of BPFO films is highly dependent on that of the SRO layer. Though the step height of STO (100) substrate is equal to one unit cell of STO crystal, the height and width of steps on the surface of SRO and BPFO are larger, which supports a step bunching growth mode on both the SRO layer and BPFO films. At zero bias voltage, the BPFO film exhibits a natural dipole polarization toward the SRO layer, which is believed to be due to the negative charge accumulation at the BPFO/SRO interface, and manifests of 71° and 109° but 180° domain walls. Doping of Pb distorted the BPFO crystal lattice to near cubic that weakens the electric anisotropy and forms a two-step flipping process. To complete a 180° dipole flipping procedure, the dipole moment first rotates 71° to adjacent states followed by a 109° rotation to the final 180° state.