Guanidinium Carbonate as a Nitriding Agent for the Synthesis of Perovskite BaTaO₂N

An ammonia-free solid-state nitridation strategy employing guanidinium carbonate (GdmC) as a carbon-nitrogen precursor is demonstrated using BaTaO₂N as a model oxynitride perovskite. While BaTaO₂N is a well-established compound, the present study focuses on the reaction chemistry enabled by GdmC under flowing N₂. Systematic comparison with other nitrogen-containing reagents reveals that GdmC provides a unique balance between nitridation capability and reducing character, enabling phase-pure BaTaO₂N formation within a short dwell time of 0.5 h. Thermal and structural analyses suggest the transient formation of carbon-nitrogen intermediates, including BaNCN species, which facilitate nitrogen incorporation into the perovskite lattice under ammonia-free conditions. Furthermore, partial La-substitution suppresses anion nonstoichiometry-related defects, leading to optical absorption characteristics comparable to those of ammonolyzed samples. These results highlight carbon-nitrogen solid-state chemistry as an effective approach for controlled nitrogen incorporation in complex oxynitride compounds.