Effect of heat treatment on internal stress in barium titanate nanocube assemblies and their dielectric property

Heat treatment is a key process to determine the dielectric properties of nanocrystalline barium titanate (BaTiO3) ceramics, which are a prospective candidate to realize further miniaturization of dielectric components in electric devices. Here, we use Raman spectroscopy and scanning microwave impedance microscopy to investigate the dependence of the internal stress and the relative permittivity of BaTiO3 nanocube three-dimensional assemblies on heat treatment temperature. We show that heat treatment in the temperature range from 700 °C to 1000 °C causes internal compressive stress in the nanocube assemblies without grain growth. The internal compressive stress is caused by formation of tight attachments between neighboring BaTiO3 nanocubes and of Ti-rich phases in the nanocube assemblies in the lower and higher temperature ranges, respectively. We also show that the relative permittivity of the nanocube assemblies at 3 GHz shows a positive correlation with the internal compressive stress. The result indicates that the internal compressive stress enhances the relative permittivity of BaTiO3 nanocubes.