Atomistic Structure of Silicon Nitride/Silicate Glass Interfaces

The structure of interfaces formed by a Si₃N₄ grain and the silica-rich intergranular amorphous phase was investigated by quantitative high-resolution transmission electron microscopy (QHRTEM). It was found that the contrast and periodicity of the HRTEM image of β-Si₃N₄ strongly depend on the specimen thickness and objective lens focus value. The different thinning rate between Si₃N₄ and the glass phase during ion-milling results in gradients of the specimen thickness at the interfaces. The interface roughness can also lead to a thickness variation of Si₃N₄ near the interface parallel to the electron beam. As a result, the HRTEM micrographs, taken from the thin specimen regions near the interfaces at a certain defocus value, show the occurrence of an artifact of an ordered structure seemingly different from Si₃N₄. The present investigations, however, showed that no ordered phase actually different from that of Si₃N₄ at the interfacial region in Si₃N₄ could be identified so far. The interfacial structure is likely direct Si₃N₄/glass bonding, rather than an ordered transition phase between the Si₃N₄ and the glass phase.