Dielectric properties of BaTiO3 thin films derived from clear emulsion of well-dispersed nanosized BaTiO3 particles

The dielectric properties of thin films with microemulsion (ME)-routed nanocrystalline BaTiO3 particles were investigated in terms of the films' crystallinity and grain size. The ME method provided a clear emulsion of well-dispersed nanocrystalline BaTiO3 particles. BaTiO3 thin films were prepared by direct spin-coating of the clear emulsion on Si/SiO2/Al2O3/Pt substrates. By varying the postannealing temperature from 600degreesC to 1000degreesC, BaTiO3 thin films of different grain sizes were prepared. A fine BaTiO3 powder was removed from the clear emulsion by adding ammonia solution to cause flocculation, followed by centrifugation and washing. A transmission electron microscope (TEM) observation revealed that the powder generated many inner voids, but the thin films did not contain inner voids, thus resulting in high crystallinity. The dielectric properties of these films were measured as functions of temperature. Polarization as a function of voltage was measured, and a ferroelectric D-E hysteresis curve was observed in the sample with a mean grain size of 18 nm. The measurement of piezoelectric hysteresis using a scanning probe microscope (SPM) also revealed ferroelectricity in a small area just below the SPM probe. Direct use of the clear emulsion of well-dispersed nanocrystalline BaTiO3 particles in the ME method enables the fabrication of BaTiO3 thin films that consist of nanocrystalline BaTiO3 grains without inner voids, and the films exhibit great dielectric performance.