22-September-2022
Boron Nitride: Structure and Electrical Properties
Boron nitride (BN) is a covalent crystal composed of nitrogen and boron atoms. It exhibits polymorphism, with two primary structural forms: one resembling diamond (cubic BN) and another mimicking graphite (hexagonal BN). The diamond-like phase ranks among the hardest known materials, while the graphite-like form serves as an excellent lubricant. Hexagonal boron nitride (h-BN), despite structural similarities to graphite, demonstrates distinct electrical behavior due to differences in electron configuration.
Why Hexagonal Boron Nitride Lacks Conductivity?
Electrical conduction mechanisms can be categorized as:
Electronic conduction: Electron-mediated (e.g., metals like Cu, Ag; graphite)
Ionic conduction: Ion-mediated (e.g., molten NaCl, NaOH)
Mixed conduction: Combined electron and ion carriers
Dielectric behavior: Polarization effects rather than charge carrier movement
h-BN's non-conductive nature stems from its atomic structure:
As a covalent compound, it contains no mobile ions for ionic conduction
Unlike graphite's sp² hybridization with delocalized π-electrons in conjugated layers, h-BN adopts sp³ hybridization
This hybridization creates a fully occupied valence band without free electrons, preventing electronic conduction
Key Structural Comparisons
Property Graphite Hexagonal BN
Hybridization sp² sp³
Bond Character Metallic/π-conjugated Strong covalent
Electron Mobility High (delocalized π) None
Conductivity Semi-metallic Insulator
The absence of free charge carriers in h-BN's strongly covalent network renders it electrically insulating, contrasting with graphite's semi-metallic behavior from its π-conjugated electron system.
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