Bimodal Grain Sized Barium Titanate Dielectrics Enabled Under the Cold Sintering Process

In barium titanate (BaTiO3) the relative permittivity varies as a function of grain size due to the influence of various sizes and scaling effects. The cold sintering process (CSP) has been applied to sinter nanocrystalline BaTiO3 (< 200 nm), however in conventionally sintered BaTiO3 a maximum relative permittivity is achieved at average grain sizes around 0.8 μm. In this work the feasibility of cold sintering 1 μm BaTiO3 inclusions in ratios of fine-grained BaTiO3 matrixes from 50 - 200 nm is investigated. Occurrences of both conformal sintering of inclusions into the matrix and constrained sintering with residual porosity are observed. Subsequently, electrical resistivities increased from 1 × 108 Ω·cm to approximately 1 × 1012 Ω·cm by a post CSP heat treatment of 500°C. Relative permittivity of annealed samples increases systematically following a logarithmic mixing law as a function of matrix grain size and increasing the ratio of inclusions to matrix.