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Calculation of Grain‐Boundary Bonding in Rare‐Earth‐Doped β‐Si 3 N 4
Author(s) -
Nakayasu Tetsuo,
Yamada Tetsuo,
Tanaka Isao,
Adachi Hirohiko,
Goto Seishi
Publication year - 1998
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1998.tb02375.x
Subject(s) - ionic radius , materials science , grain boundary , doping , cluster (spacecraft) , ion , intergranular corrosion , rare earth , ionic bonding , grain growth , crystallography , mineralogy , condensed matter physics , chemical physics , grain size , metallurgy , chemistry , physics , microstructure , optoelectronics , organic chemistry , computer science , programming language
First‐principles molecular orbital calculations are performed by the discrete variational Xalpha method using model clusters of rare‐earth‐doped β‐Si 3 N 4 and the interface between prismatic planes of β‐Si 3 N 4 and intergranular glassy films. On the basis of the total overlap population of each cluster, the rare‐earth ions are implied to be stable in the grain‐boundary model, while they are not stable in the bulk model. These results are consistent with experimental observations showing significant segregation of Ln 3+ ions at the grain boundary and no solubility of Ln 3+ into bulk β‐Si 3 N 4 . Grain‐boundary bonding is weakened with an increase of the ionic radius of the rare‐earth ions, which provides a reasonable explanation for the ionic size dependence of the crack propagation behaviors as well as the growth rate of the prismatic plane in the rare‐earth‐doped β‐Si 3 N 4 during liquid‐phase sintering.