Crystalline–disordered–crystalline transition in nitrogen–carbon materials

Abstract

Nitrogen–carbon (N–C) materials range from graphitic carbon nitride (g-CN) to graphite with nitrogen defects. Between these two crystalline extremes lies a spectrum of semi-crystalline and disordered materials. The question is whether these structural transitions are related to material’s composition, and if yes, how? Here, we answer these questions based on experimental and computational investigations on the structural evolution in N–C systems and their correlation with the chemical and electronic properties. Crystalline g-CN is used as the starting material with a systematical reduction in its N-content through heat treatment. As the N-content reduces, crystalline g-CN transitions into N-containing disordered carbons followed by N-containing graphitic carbons. The experimentally deduced electronic properties of the N–C systems with decreasing N-content are validated by theoretical methods using Density Functional Theory (DFT) approach. A qualitative match between the experimentally deduced and theoretically computed electronic properties indicate crystalline to disordered to crystalline structures in such materials at two noticeable transition points around the N/C ratios of 0.35 and 0.17, respectively.