Particle Structure Analysis of Highly-dispersed Barium Titanate Nanoparticles Obtained from Barium Titanyl Oxalate Nanoparticles and Their Dielectric Properties

摘要

Barium titanate (BaTiO_3) nanoparticles were prepared by two-step thermal decomposition method of barium titanyl oxalate nanoparticles with a size of 30 run. The BaTiO_3 particle sizes were changed from 12.3 to 142 nm by control of temperature at 2nd step. The X-ray diffraction (XRD) measurement revealed that a clear splitting of 002 and 200 planes was observed over 40 nm, and the da ratio of 1.0089 was obtained for the BaTiO_3nanoparticles with a size of 62.3 nm. This high da ratio in the BaTiO_3 nanoparticles suggested that its mesoscopic particle structure was composed of very thin surface cubic layer below 5 nm. Thus, synchrotron XRD data were analyzed using a "two layers" model and a "three layers" model. The Rietveld analysis using the three layers model resulted in the particle structure with a cubic layer thickness of 2.5 nm and structure gradient layer thickness of 7.5 nm. Finally, the dielectric constant of these BaTiO_3 nanoparticles with thin surface cubic layer was measured at room temperature, and the maximum dielectric constant over 30,000 was obtained at the nanoparticles with a size of 83.6 nm.