Ferroelectric properties of randomly oriented Bi1 − xPrxTi3O12 thin films fabricated by a sol-gel method

Praseodymium-substituted bismuth titanate, Bi3.4Pr0.6Ti3O12 (BPT), thin films were successfully fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by a sol-gel method. Fabricated BPT thin films were found to be random orientations, which were confirmed by X-ray diffraction experiment and scanning electron microscope analysis. The remanent polarization (2Pr) and the coercive field of the BPT thin film annealed at 650 °C were 62 μC/cm2 and 205 kV/cm, respectively, at an applied electric field of 320 kV/cm. The measured 2Pr of the randomly oriented BPT thin film is larger than those of Bi4 − xLaxTi3O12 (x=0.75) and Bi4Ti3O12 thin films, and comparable with those of other lanthanide-substituted Bi4Ti3O12 thin films. The BPT thin film exhibits a good fatigue resistance up to 1.5×1010 switching cycles at a frequency of 1 MHz with applied electric field of 120-240 kV/cm. These results indicate that the randomly oriented BPT thin film is a promising candidate among ferroelectric materials useful in lead-free nonvolatile ferroelectric random access memory applications.