Barium Titanium Oxynitride From Ammonia-Free Nitridation Of Reduced Batio3

We investigated the nitridation of reduced BaTiO3, BaTiO2.60H0.08, corresponding to an oxyhydride with a large concentration of O defects (>10%). The material is readily nitrided under flowing N-2 gas at temperatures between 400 and 450 degrees C to yield oxynitrides BaTiO2.6Nx (x = 0.2-0.22) with a slightly tetragonally distorted perovskite structure, a approximate to 4.01 and c approximate to 4.02 angstrom, and Ti partially remaining in the oxidation state III. The tetragonal structure was confirmed from Raman spectroscopy. N-14 MAS NMR spectroscopy shows a single resonance at 270 ppm, which is typical for perovskite transition metal oxynitrides. However, largely different signal intensity for materials with very similar N content suggests N/O/vacancy ordering when prolonging nitridation times to hours. Diffuse reflectance UV-VIS spectroscopy shows a reduction of the intrinsic band gap to 2.4-2.45 eV compared to BaTiO3 (similar to 3.2 eV). Mott-Schottky measurements confirm n-type conductivity and reveal a slight negative shift of the conduction band edge from -0.59 V (BaTiO3) to similar to-0.65 eV.