Defects, impurities and inclusion–host interfaces in diamond: an atomic-scale physico-chemical framework

The term “inclusion” is widely used in diamond research to describe internal features that differ fundamentally in their physical nature. In practice, atomic-scale lattice defects and chemically distinct foreign phases are frequently conflated, leading to ambiguity in the interpretation of microstructural observations. This paper presents a conceptual physico-chemical framework that distinguishes lattice-incorporated defects from true inclusions based on crystalline continuity and interface physics. Rather than treating defects and inclusions as a continuum, the framework defines them as categorically distinct entities separated by the presence or absence of lattice discontinuity. The analysis focuses on the response of the diamond host lattice to mechanically incompatible second phases. Microstructural features commonly observed at the optical scale are interpreted as elastic, defect-mediated, or brittle accommodation mechanisms within the host crystal. By clarifying the physical categories underlying these observations, the framework provides consistent interpretive boundary conditions for the analysis of defects and inclusions in crystalline solids.