Cation‐Aided Joining of Surfaces of β‐Silicon Nitride: Structural and Electronic Aspects

An atomic‐scale approach has been applied to the examination of both the physical and electronic structures of stable surfaces of β‐Si 3 N 4 . Sterical constraints prevent the (001) surface from effective chemical reaction with the interface. The theoretical surface‐to‐surface bonding is investigated by using a periodical tight‐binding approach. Based on the interpretation of the density of states, the balance of the number of states and electrons is performed for stoichiometric Si 3 N 4 , ideal N‐terminated (110) surfaces, oxygen‐overlayered (110) slabs, and the metal monolayer with which the slabs are brought into contact. The stable electronic configuration, which is attained when the cation binds to the interface, represents the electronic driving force behind the diffusion of the additive and/or impurity atoms toward grain boundaries. The different bonding propensities of the (001) and (110) surfaces imply that effective bonding of the planes parallel to the c ‐direction to the interphase restrains the crystal from growth in the lateral direction. Conversely, geometry‐constrained bonding of the (001) planes allows the crystal growth that produces the rod‐shaped β‐grains.