Atomic Resolution Transmission Electron Microscopy of the Intergranular Structure of a Y₂O₃‐Containing Silicon Nitride Ceramic

Abstract

High‐resolution transmission electron microscopy (HRTEM) employing focus‐variation phase‐reconstruction methods is used to image the atomic structure of grain boundaries in a silicon nitride ceramic at subangstrom resolution. Complementary energy‐dispersive X‐ray emission spectroscopy experiments revealed the presence of yttrium ions segregated to the 0.5–0.7‐nm thin amorphous boundary layers that separate individual grains. Our objective here is probing if yttrium ions attach to the prismatic planes of the Si3N4 at the interface toward the amorphous layer, using Scherzer and phase‐reconstruction imaging, as well as image simulation. Crystal structure images of grain boundaries in thin sample (<100 Å) areas do not reveal the attachment of yttrium at these positions, although lattice images from thicker areas do suggest the presence of yttrium at these sites. It is concluded that most of the yttrium atoms are located in the amorphous phase and only a few atoms may attach to the terminating prism plane. In this case, the line concentrations of such yttrium in the latter location are estimated to be at most one yttrium atom every 17 Å.

Dynamic behavior of nanometer-scale amorphous intergranular film in silicon nitride by in situ high-resolution transmission electron microscopy

“…The appearance of additional crystal planes in the interface region is probably due to partial crystallization of the IGF during the time spent at high temperature. However, in contrast to previous observations 7, 8 the crystallization of the IGF occurred at a relatively low annealing temperature. We also observe that the thickness of the IGF changes remarkably during in situ heating.…”

“…Note that one additional plane in the interface region has formed during the cooling, which is also found in quenching and annealing investigations. 8,14 Another noticeable feature is that the IGF has reappeared with a thickness of about 0.6 nm when the sample is observed at room temperature again.…”

“…With the advent of aberration-corrected STEM it seems now to become possible to characterize the detailed atomic structure in such localized IGF volumes using a fine electron probe with a diameter of less than 1Å. [7][8][9] First results show that rare-earth dopants preferentially segregate to the (amorphous) film/(crystalline) grain interface.…”

Three-dimensional organization of rare-earth atoms at grain boundaries in silicon nitride

“…The terminating crystal plane is described by a series of half-hexagons consisting of three Si columns each, as observed by others. 9 Viewed parallel to ͓100͔, the grains appear as an array of spots, each indicating the position of two nearby ͑0.038 nm͒, though unresolved, Si columns. The crystals terminate on a row of Si columns in a manner consistent with the row of halfhexagons observed parallel to ͓001͔.…”

Projected Potential Profiles across Intergranular Glassy Films

“…12 -14 High frequency components of the phase across the IGF of yttria doped Si 3 N 4 were mapped with atomic resolution using high resolution images at different foci. 15 Off-axis electron holography has been used to determine the local electrostatic potential and associated space charge across an IGF 16 while electron diffraction experiments were able to provide IGF potential profiles averaged over large distances along the boundary.…”