Electroconductive silicon nitride-titanium nitride ceramic substrates for CVD diamond electrode deposition

The present investigation was carried out to develop dense ceramics of silicon nitride-titanium nitride (Si3N4–TiN) with low electrical resistivity and excellent mechanical properties. The objective was to employ these ceramics as substrates of conductive diamond electrodes produced by chemical vapor deposition (CVD) for electrochemical applications. TiN powder was added to a Si3N4 matrix powder composition at varying volume fractions (21–30%). Disc-shaped samples were fabricated by mixing and pressing the powders, followed by pressureless sintering. The crystalline phase composition and microstructure were analyzed using X-ray diffraction and scanning electron microscopy, while the electrical resistivity was measured with a four-point probe configuration. The composites transitioned from insulating to conductive behavior between 23 and 27%vol TiN. The developed compositions displayed superior hardness, fracture toughness, elastic modulus, and thermal conductivity compared to the Si3N4 matrix. Notably, the composition containing 30%vol TiN displayed noteworthy properties, including a hardness value of 16.1 GPa, fracture toughness of 7.0 MPa m1/2, and electrical resistivity of 8.9 × 10−1 Ω cm. Finally, the proof-of-concept experiment demonstrated the potential of Si3N4–TiN composites as robust and electroconductive substrates for depositing conductive diamond electrodes. This was achieved by successfully depositing conductive diamond films on Si3N4–TiN substrates using the Hot Filament Chemical Vapor Deposition (HFCVD) technique.