NNR IN RAPIDLY ROTATED METALS By - Nottingham eTheses ...

- 29 -
where En are the Zeeman energy levels (-yM n). This leads to
the expression
with
11a
1
f (I)
40
f (I) (eQ)2cT*2E(T*) JE1(co) + 4E2(o) I
21 +3
I2(2I - 1)
Such an equation is not specific to zinc blende crystal lattices
because all the structure parameters are included in the terms
cEn_m(()0). From Mieher's calculated values of E+1(co) and E+2(oo)
an isotropic relaxation time is predicted, which is given by
where
T=
A
1r
Af (I)
e2 YQ ZT*2E (T*)
3305c 1983
40
71d2v 3 a2
The term (e2yQ/r5) is a measure of the strength of the electric
quadrupole interaction between nuclei, r being the nearest-neighbour
separation and ya scalar.
The weakness of the above expression is that any indirect
contributions to the nulcear quadrupole coupling are included only
through the multiplying factor y. In ionic crystals the electron
charge cloud surrounding each nucleus is distorted from spherical
symmetry by the electric field gradient arising from the other ions.
This leads to an additional contribution to the nuclear quadrupole
coupling, the magnitude of which can be estimated from the value
of the Sternheimer anti-shielding factor
(3,24)
for the particular
ion. However, compounds with a zinc blende type lattice structure
(2.29)