Room temperature ferromagnetism and CH4 gas sensing of titanium oxynitride induced by milling and annealing

We report on the room temperature ferromagnetism and CH4 gas sensing of titanium oxynitride prepared by milling and annealing at 1100 °C in a nitrogen gas environment. Structural analyses revealed a metastable orthorhombic TiO2 phase after milling for 120 h. The 120 h milled TiO2 particles and subsequently annealed in nitrogen gas at 1100 °C showed the formation of titanium oxynitride (TiOxNy) with a tetragonal crystal structure. An FCC metastable TiOxNy phase was also observed with a lattice parameter a = 4.235 Å. The vibrating sample magnetometer and electron paramagnetic analyses showed that the milled and TiOxNy samples possess room temperature ferromagnetism. Gas sensing measurements were carried out toward CH4 and H2 gases. The TiOxNy nanostructures demonstrated higher sensing response and selectivity to CH4 gas at room temperature. The enhanced response of 1010 and sensitivity of 50.12 ppm−1 at a concentration of 20 ppm CH4 are associated with higher surface area, pore diameter and surface defects such as oxygen vacancies and Ti3+, as evidenced from the Brunauer–Emmet–Teller, photoluminescence, electron paramagnetic resonance and x-ray photoelectron analyses.