Page 157 - Polymer-based Nanocomposites for Energy and Environmental Applications

132 Polymer-based Nanocomposites for Energy and Environmental Applications

Fig. 5.1 Mode of polarization of a –s s
dielectric in presence of external i i
field (E, electric field applied; d, – + – + – +
dielectric distance; and σ i , surface
charge density). – + – +
Reprinted with permission from + –
Azadmanjiri J, Berndt CC, Wang J,
Kapoor A, Srivastava VK, Wen C. – + – + – +
A review on hybrid nanolaminate
materials synthesized by deposition – + – + – + →
techniques for energy storage E
applications. J Mater Chem
– + + – +
A 2014;2:3695–708. Copyright 2014 –
The Royal Society of Chemistry.
– + – + – +
–s i s i

d

Metal oxide dielectrics have a relatively low temperature coefficient (τ) and low tan-
gent loss (tan δ); however, the relative permittivity (ε r ) of metal oxide dielectrics is
generally <100 [14].
Ferroelectrics are the another type of dielectrics where the residual dipoles result
from static atomic displacements that display principally perovskite structures [14].
They possess relatively higher dielectric permittivity ( 200) [14] and have been fur-
ther improved for the perovskites, ferroelectric oxides (Pb(Zr,Ti)O 3 ) and relaxor
oxides (PbMg 1/3 Nb 2/3 O 3 ) to above 1000 [2,8,9]. A very critical limitation with the
metal oxides is the narrow bandgap and subsequent large leakage current [9,19].In
addition, most of them are thermodynamically unstable when exposed to a silicon
wafer at high temperatures [9,20]. The thermal stability of some of the metal oxides
has been enhanced using an additive that results in good thermal stability and a large
bandgap [21–25]. However, the relative permittivity of such materials may reduce
due to the relatively low dielectric constant of the additive and enhanced leakage
current [1,24].

5.1.2 Dielectrics and the energy storage capability

Nanodielectrics as energy storage devices have a key role in modern electronics and
electric power systems. Previously, utilized conventional micrometer-sized particles
are being substituted with nanodimension metal oxide particles in nanodielectric sys-
tems [26-29]. As can be seen from Eq. (5.1), electric energy storage density (U)in a
linear dielectric material depends linearly on the permittivity of the material (k) and
the square of the dielectric breakdown strength (DBS) (E b ).