Abstract :
A recently developed model of grain
boundary (GB) segregation, in terms of the five
macroscopic parameters of GB orientation, has been
exercised to explore the anisotropy of GB segregation.
The five macroscopic GB orientation parameters
are defined by means of the orientations of the two
crystallographic planes that terminate the crystals on
either side of the GB, and a twist angle. Some
important conclusions include the following: (a) the
composition of a boundary depends on all five
parameters of GB orientation, (b) the segregation
profile across a GB depends on the two planes which
terminate the adjacent crystals, (c) the composition
profile across GB’s terminated by identical crystallographic
planes is symmetric, but is asymmetric when
GB’s are terminated by different planes, and (d) the
strength of the segregation on one side of a GB
influences the extent of segregation on the other.
Some experimental results on Nb-doped TiO2 are
presented in order to verify above predicted trends. In
addition, it is shown that the model predicts the
possibility of anisotropic GB wetting transitions as
two-phase coexistence is approached
