32
T. B. Asafa et al.
position in degree. Further, the dislocation density S, a measure of number of defects
and vacancies in the crystal, and micro-strain (ε) are determined from Eqs. 8 and 9.
S =
1
D 2
(8)
ε =
βcosθ
4
(9)
For more analysis, the volume of the nanoparticles V, volume of hexagonal unit
cell v, and number of unit cells present in a particle (ratio V
v) are calculated from
the relations:
V =
4
3
π
D
2
3
(10)
v =
3a
2 c
2
(11)
n = 1.621
D
3
a 2 c
(12)
The XRD pattern for ZnO nanopowder shown in Fig. 11a agreed well with the
reported reference patterns of wurtzite ZnO (hexagonal phase, JCPDS file 75-0576).
The mean crystallite size was evaluated for the highest diffraction peak along the
<101> plane to be 34.2 nm (Adedokun et al. 2018). For the TiO 2 powder, the XRD
pattern (Fig. 11b) matched with TiO 2 anatase tetragonal phase (JCPDS file 71-1168).
The mean crystallite size was 39.10 nm (Adedokun et al. 2017a, b).
Fig. 11 XRD pattern of a ZnO nanopowder (Adedokun et al. 2018), b TiO 2 powder (Adedokun
et al. 2017a, b)