Biomedical Engineering Reference
In-Depth Information
15.4
Arrhenius plots of LiI and 0.6 LiI:0.4 Al
2
O
3
composite.
dielectric phase. In these nanocomposites, the dopant also remains insoluble
in the host matrix and exists as a physically distinct phase of the bulk
structure even after processing (sintering) at high temperatures. It was Liang
who first demonstrated, in 1973, that the intrinsic conductivity of lithium
iodide doped with 35-45mol% Al
2
O
3
was enhanced by orders of magnitude
as compared to the conductivity of LiI (Liang, 1973). The enhancement in
conductivity has been explained on the basis of space charge formation at
the LiI-Al
2
O
3
interface (Maier, 1995). Since the pioneering work of Liang
(1973) almost four decades ago, the phenomenon has been demonstrated in
several other systems ranging from lithium to oxygen ion conducting
heterogeneous solids (Kumar, 2007; Kumar and Thokchom, 2008).
Figure 15.4 shows Arrhenius plots of conductivity of LiI and
0.6 LiI:0.4 Al
2
O
3
nanocomposites in the 27 to 77
C temperature range
(Kumar, 2007). The conductivity of the nanocomposite specimen increases
by nearly two orders of magnitude by doping LiI with 40 mol% Al
2
O
3
. The
activation energies associated with the transport of ions in LiI and
0.6 LiI:0.4Al
2
O
3
specimens are 0.51 and 0.57 eV, respectively. An increase
in the activation energy by over 10% reflects a deviation in the transport
mechanism of the nanocomposites that may be attributed to the space
charge mediation. The conductivity of the nanocomposite is reproducible
and stable within the temperature range of 27 to 77
8
C (Kumar, 2007).
The space charge mediated transport mechanism was elucidated by
Kumar and Thokchom (2007) using a glass-ceramic material,
8
lithium
