Chiara Ricca^1,2, Tristan Blandenier¹, Valérie Werner³, Xing Wang¹, Simone Pokrant³, Ulrich Aschauer^1,2,3*

1 Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland

2 National Centre for Computational Design and Discovery of Novel Materials (MARVEL), 1015 Lausanne, Switzerland

3 Department of Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Str. 2A, A-5020 Salzburg, Austria

* Corresponding authors emails: ulrich.aschauer@unibe.ch

DOI10.24435/materialscloud:ee-v0 [version v1]

Publication date: Apr 25, 2023

How to cite this record

Chiara Ricca, Tristan Blandenier, Valérie Werner, Xing Wang, Simone Pokrant, Ulrich Aschauer, Conversion of La₂Ti₂O₇ to LaTiO₂N via ammonolysis: An ab-initio investigation, Materials Cloud Archive 2023.69 (2023), https://doi.org/10.24435/materialscloud:ee-v0

Description

Perovskite oxynitrides are, due to their reduced band gap compared to oxides, promising materials for photocatalytic applications. They are most commonly synthesized from {110} layered Carpy-Galy (A₂B₂O₇) perovskites via thermal ammonolysis, i.e. the exposure to a flow of ammonia at elevated temperature. The conversion of the layered oxide to the non-layered oxynitride must involve a complex combination of nitrogen incorporation, oxygen removal and ultimately structural transition by elimination of the interlayer shear plane. Despite the process being commonly used, little is known about the microscopic mechanisms and hence factors that could ease the conversion. Here we aim to derive such insights via density functional theory calculations of the defect chemistry of the oxide and the oxynitride as well as the oxide's surface chemistry. Our results point to the crucial role of surface oxygen vacancies in forming clusters of NH₃ decomposition products and in incorporating N, most favorably substitutionally at the anion site. N then spontaneously diffuses away from the surface, more easily parallel to the surface and in interlayer regions, while diffusion perpendicular to the interlayer plane is somewhat slower. Once incorporation and diffusion lead to a local N concentration of about 70 % of the stoichiometric oxynitride composition, the nitridated oxide spontaneously transforms to a nitrogen-deficient oxynitride.

Materials Cloud sections using this data

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Keywords

SNSF MARVEL Oxynitride Ammonolysis Defects