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Low‐Frequency Measurements on the Grain‐Boundary Internal Friction Peak in Chlorine‐Doped Silicon Nitride
Author(s) -
Pezzotti Giuseppe
Publication year - 2001
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.1151-2916.2001.tb01016.x
Subject(s) - grain boundary , misorientation , materials science , crystallite , relaxation (psychology) , silicon nitride , activation energy , grain size , condensed matter physics , doping , grain boundary diffusion coefficient , mineralogy , silicon , composite material , microstructure , metallurgy , chemistry , physics , psychology , social psychology , optoelectronics , organic chemistry
A procedure is shown to quantitatively analyze the morphology of the internal friction peak resulting from grain‐boundary sliding. A Si 3 N 4 polycrystal containing chlorine‐doped SiO 2 at grain boundaries is selected as a model system for discussing chemical (e.g., anion) gradients at glassy grain boundaries. In this model material, grain boundaries lodging Cl − anions show nonuniform thickness characteristics, which suggests a non‐negligible dependence of the intergranular SiO 2 ‐network structure upon grain misorientation. Both chemical and microstructural inhomogeneities existing in a polycrystalline ceramic body can result in peak broadening. The key for separating broadening contributions of chemical gradients from grain‐size/morphology distributions resides in analyzing the peak‐width change upon damping frequency. Groups of grain boundaries with different chemical characteristics may produce broadening because different peak components are generated that obey a spectrum of activation energies. On the other hand, microstructural inhomogeneities obey a single activation energy, but they generate a distribution of relaxation times. As a result, when a chemical gradient is present at grain boundaries, the peak may shift upon changing damping frequency with obeying a true activation energy, but its width increases with decreasing damping frequency. When peak broadening results only from microstructural inhomogeneities, the peak width is independent of damping frequency.