Fabrication of nitrogen-doped titanium oxide/silica core–shell particles and their electrical conductivity

The present work proposes a method for fabricating partially nitrided titanium oxide (TiON) particles coated with silica shells (TiON/SiO2) using a sol–gel process and describes their electronic insulation properties. Commercially available TiON particles with an average size of 90.3 ± 29.9 nm were used as the core particles. The silica coating of the TiON particles was performed using a sol–gel method with 15 M tetraethylorthosilicate (TEOS) in H2O and 1.2 × 10−3 M NaOH in an ethanol solution containing 1.0 × 10−2 M TiON particles at 35 °C. Successful silica coating was confirmed using transmittance electron microscopy, dynamic light scattering, electrophoretic light scattering, X-ray photoelectron spectroscopy and optical spectroscopy. The silica shell thickness increased in the range of 3.6–11.4 nm with increasing TEOS concentrations from 2.0 × 10−3 to 9.0 × 10−3 M. The volume resistivity of a powder of the TiON/SiO2 particles was larger than 2.8 × 106 Ω cm, even under pressure, i.e., it did not decrease remarkably with an increase in pressure applied to the powder from 10 to 200 kg-f/cm2. The silica shells were hypothesized to prevent the TiON particles from contacting other TiON particles.