Thermodynamically stable polymorphs of nitrogen-rich carbon nitrides: a C3N5 study

Abstract

We have carried out an extensive search for stable polymorphs of carbon nitride with C₃N₅ stoichiometry using the minima hopping method. Contrary to the widely held opinion that stacked, planar, graphite-like structures are energetically the most stable carbon nitride polymorphs for various nitrogen contents, we find that this does not apply for nitrogen-rich materials owing to the high abundance of N–N bonds. In fact, our results disclose novel morphologies with moieties not previously considered for C₃N₅. We demonstrate that nitrogen-rich compounds crystallize in a large variety of different structures due to particular characteristics of their energy landscapes. The newly found low-energy structures of C₃N₅ have band gaps within good agreement with the values measured in experimental studies.