Ferroelectric thin films are of interest because they have the potential to be used in a variety of devices, such as nonvolatile memories, room temperature pyroelectric devices, electro-optical devices, and microelectromechanical systems, and ferroelectrics are an important part of a variety of applications. Ferroelectrics and a broader spectrum of polar materials have been used in RF devices and non-volatile memory in thin film form for some years now. Ferroelectric thin film components for sensor and actuator applications, as well as adjustable microwave circuits, are also being developed. Because the dielectric constant changes rapidly at the phase transition temperature, the phase transition temperature of ferroelectric materials may be measured by measuring the change in dielectric constant with increasing temperature. Based on the temperature change of dielectric monitoring, we present the measurement of the phase transition temperature of ferroelectric composite oxides BLT (Bi3.25La0.75Ti3O12) as well as Co and Fe doped BLT bulk ceramics for optoelectronic devices. With varied doping concentrations, we created lanthanum-modified bismuth titanate-based ceramics BLCT(Bi3.25La0.75Co1Ti2O12)and BLCFT(Bi3.25La0.75Fe0.25Co0.75Ti2O12). We discovered that all of the compounds crystallized in an orthorhombic form using X-ray diffraction research. We evaluated their size distribution and morphology using scanning electron microscope data. The ultraviolet-visible (UV-Vis) absorption spectra of the produced powders were used to determine the band gap. The link between the dielectric response and the temperature of the target in a tube furnace was determined using an LCR instrument. These observations allowed us to see a progressive increase in the dielectric constant as temperature increased up to the transition temperature (Tc) and then a reduction, allowing us to establish their phase transition temperature. As a result, we can say with certainty that all doped bismuth titanates have a high enough phase transition temperature to sustain ferroelectric characteristics above room temperature.For the rapid development of wearable electronic devices, flexible, large-scale, fatigue-free, and non-volatile memories are emerging technology targets in various fields, including wearable devices, electronic skins, and other flexible electronics. We found that under different conditions, halide films deposited on rigid substrates such as SrTiO3 by high temperature can only be used in the electronics industry and have a low application rate in flexible electronics. Here, we prepared BLT (Bi3.25La0.75Ti3O12), BLCT (Bi3.25La0.75Co1Ti2O12) and BLCFT(Bi3.25La0.75Fe0.25Co0.75Ti2O12) films of ferroelectric materials by rf sputtering on 100um glass substrates, which showed processability and flexibility. We obtained ferroelectric films with a film thickness of 200 nm by rf sputtering. The crystallinity was well analyzed by XRD data and the surface morphology was observed by SEM and AFM. From our bending tests, the ferroelectricity can be maintained at a bending radius of 4 mm, and after bending cycles up to 100 times we found fatigue-free properties of the ferroelectric film after remeasuring the capacitance comparing the data when bending and flat. In addition, the BLT ferroelectric films we made use of 100um glass as the substrate, which has a significant advantage over other flexible substrates in terms of high-temperature resistance and stiffness. Therefore, we believe that these flexible ferroelectric film memories will be used in a wider range of flexible electronic products.Driven by the growing demand for renewable energy and cleanliness, various solar cells and solar materials have been investigated to convert light energy into electricity through the photovoltaic effect. We fabricated BLT (Bi3.25La0.75Ti3O12) and BLCT (Bi3.25La0.75Co1Ti2O12) films by RF sputtering, and then modified BLCFT(Bi3.25La0.75Fe0.25Co0.75Ti2O12) films by RF sputtering to improve the photovoltaic power generation performance of BLT through the composition of dual ferroelectric semiconductors. The photovoltaic tests showed that the photovoltaic performance of BLT and BLCT films was superior after plating with BLFCT. We modified the BLT and BLCT films by FBLFCT films to narrow the band gap value so that the films can absorb more visible light range and thus improve the efficiency of the photovoltaic reaction. The current density with light is significantly increased by the modification of BLT films doped with Fe and Co. Therefore, this study is significantly helpful to improve the efficiency of the photovoltaic reaction of ferroelectric thin films.For decades, a variety of ferroelectric oxides have been used to study the ferroelectric-photovoltaic (FE-PV) system, which employs a homogeneous ferroelectric material as a light-absorbing layer. It is possible to increase the photovoltaic activity of materials by changing the bandgap in ferroelectric complex oxides. This phenomenon has been shown in epitaxial thin films of the ferroelectric complex oxide Bi3.25La0.75Ti3O12 (BLT) doped with Fe and Co. In comparison to undoped BLT, Co (BLCT) doping and combined Fe, Co (BLFCT) doping result in a lowering of the bandgap, as well as a notably more efficient visible light absorption. The BLFCT film has a photocurrent density that is 32.2 times that of BLT films, which is connected to its bandgap decrease. This simple doping technique may be used to tune the bandgap of additional wide-bandgap complex oxides, allowing them to be used in solar energy conversion or optoelectronic applications.