Reductive-defect-suppressed titanium oxynitrides via Ca3N2-assisted topochemical nitridation

Abstract

Transition-metal oxynitrides are promising for photocatalysis and dielectric applications owing to their visible-light absorption and tunable band structures. Conventional ammonolysis, however, proceeds under reducing conditions that cause electron doping and limited compositional control. Here, we present a one-step, ammonia-free topochemical nitridation using Ca₃N₂ as a solid nitrogen source. BaTiO₃ reacts with Ca₃N₂ at 550 °C via a stoichiometric 3O²⁻/2N³⁻ anion-exchange process to yield orange BaTiO_3−3x/2N_x with Ti³⁺-related reductive defects suppressed below detectable levels. The resultant oxynitrides exhibit tunable bandgaps, high crystallinity, and visible-light photoactivity, while the CaO byproduct can be readily removed by washing. This method establishes Ca₃N₂ as a safe and effective reagent for controlled, ammonia-free oxynitride synthesis.