Preparation of Freestanding Films Using Barium Titanate Nanoparticles and Their Electrical and Optical Properties

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BaTiO3 ferroelectric perovskites have been applied to a variety of applications, including multilayer ceramic capacitors (MLCC), piezoelectric transducers, actuators, thermistors with positive temperature coefficient, and ultrasonic devices. In the development of MLCC manufacturing processes, understanding the relationship between the particle size and structure of barium titanate material particles, the phase transition temperature to the ferroelectric phase, and dielectric properties is very important for understanding the design and transformation of the material particles. We have studied the evaluation of phase transition temperatures using X-ray diffraction and SHG analysis.In this study, barium titanate nanoparticles with a diameter of approximately 50 nm were used to formulate a paste by mixing with solvents and resins. The production method was modeled on the already commercialized Ag paste method. After screen printing, the paste was heat-treated at 110°C to solidify to form a freestanding film. The creation of freestanding films allows for easy control of film thickness without the influence of the substrate, which is expected to expand the range of applications. After further heat treatment at over 1000°C, Pt electrodes were formed on both sides of the film by sputtering, and the dielectric constant and its temperature change were evaluated as a parallel plate capacitor. Typical film thickness is 200 μm. As a result, it was found that the dielectric constant was higher than that of the bulk material, with a maximum value around 120°C. The loss was found to be very small, less than 0.05. These results indicate that the material is highly practical. XRD results also confirmed the existence of a phase transition temperature around 120°C. Furthermore, SHG results also corroborate the XRD results. Details of the paste preparation method, freestanding films, evaluation by cross-sectional SEM after heat treatment, temperature dependence of dielectric properties, and evaluated nanoparticle properties will be discussed.