9 Mössbauer Spectroscopic Studies on Atomic Diffusion in Materials
457
1
τ
=
1
τ 0
exp
−
E m
k B T
.
(9.19)
We consider two jump models on an empty bcc lattice: (A) the jump vectors
from the body centre to the eight corner sites, as in Fig. 9.10(a), and (B) those
from the body centre to the six octahedral sites, as in Fig. 9.10(b). We present the
line broadening normalized by the natural linewidth as functions of the angle and
temperature in Figs. 9.11(a) and 9.12(a), respectively, for the jump models of (A) and
(B). The line broadenings depend strongly on the jump models. Also, the Mössbauer
spectra in Figs. 9.11(b) and 9.12(b) show that the linewidths increase so quickly
that the spectra disappear apparently within the temperature width of 100 K above
300 K. When we measure an angular dependence of the linewidth of the Mössbauer
spectrum experimentally, we will be able to obtain the jump vectors in a crystal
lattice.
(a)
(b)
Fig. 9.10 (a) Jump vectors, R j (j = 1, 8) from body centre to eight corner sites in bcc lattice and
(b) those from body centre to octahedral sites, R j (j = 1, 6). θ is the angle between [100] and wave
vector k when the wave vector changed on x–y plain. The lattice constant of a is 0.2855 nm for
α-Fe
Fig. 9.11 (a) Line broadenings for different direction of wave vector k as function of temperature,
and (b) Mössbauer spectra for [100] direction as function of temperature, which are simulated based
on the jump model Fig. 9.10 (a)