Atomistic Structure of Calcium Silicate Intergranular Films Between Prism and Basal Planes in Silicon Nitride: A Molecular Dynamics Study

Abstract

Molecular dynamics simulations of approximately 15 Å thick intergranular films (IGFs) containing SiO 2 and CaO in contact with two surface terminations of the prism (1010) and basal planes (0001) of Si 3 N 4 were performed using a multibody interatomic potential. Samples with the same composition (1.5 mol% CaO) and number of atoms but different crystal planes (i.e., the prism and basal planes of Si 3 N 4 ) were studied. In both the prism and basal cases, the IGF in the final configuration is well-ordered in the interface region. A small number of N ions from the crystal moved into the IGF near the interface, and O ions moved into the N sites in the crystal, indicating the formation of a Si-O-N interface. In addition, Ca ions do not segregate to the IGF-crystal interface. The bonding characteristics of the O ions at the interface with neighbor Si ions are different in the prism and basal cases. Such difference may be explained by the difference in the two crystal Si 3 N 4 surfaces. The Si-O bond length of the IGF has a range from 1.62 Å to 1.64 Å, consistent with recent experimental findings.

Electronic structure and bonding of intergranular glassy films in polycrystallineSi3N4:Ab initiostudies and classical molecular dynamics simulations

“…The snapshot of atomistic structure uses only a thin slice of the actual system perpendicular to the plane of the figure to enable better visualization of the structure and bonding. Compared to previous studies of IGF's in contact with ideal ␤ -Si 3 N 4 crystal surfaces, 30,31 atoms in the IGF are less ordered in the interface region. This is shown with more detail in Fig.…”

“…Periodic boundary conditions were applied in the x, y, and z directions. Table III shows the previously discussed 31,32 heat and quench process used in the simulations. All atoms in the Si 3 N 4 crystal were immobilized from 10 000 K to 4000 K while the atoms in the IGF went through the melt-quench process to form the amorphous IGF.…”

“…[22][23][24][25] There have been several studies of IGF's using molecular dynamics ͑MD͒ simulations. [26][27][28][29][30][31][32][33] Results showed ordering into the amorphous IGF induced by contact with the crystal surfaces in both the oxide crystals ͑alumina͒ ͑Refs. 29 and 33͒ and the nitride crystals ͑silicon nitride͒ ͑Refs.…”

Final report

“…This should have significant implications in the kinetic behavior of these systems during sintering and local compositional changes or particle rearrangements. We also observed strained siloxane bonds at the IGF/crystal interfaces, with less strain farther from the interface 1,2 . Results of Si-O bond lengths are consistent with the newest pair distribution functions found experimentally for the 1nm IGFs between silicon nitride crystals 4 .…”

“…Interestingly, in the case of the IGF between β-Si 3 N 4 crystals, the MD simulations showed that growth of the basal plane in the <0001> direction is more likely than growth along the < 101 0 > direction 1,2 . Hence, the results of our simulations imply different types of crystal growth for the two systems studied: preferential growth along the prism plane normal in the alumina case, but preferential growth along the basal plane normal in the nitride case.…”