Alternative Caloric Energy Conversions - Magnetocaloric Energy Conversion: From Theory to Applications - page 418

Table 10.8 Pyroelectric coef cient of some ceramic and polymer materials
Material T a Material type ( ° C) p

(

References

Cm − 2 K − 1 ) µ

BaTiO 3 Ceramic 20 - 47 330 [ 1 ]

Pb(ZrTi)O 3 Ceramic 20 100 260 [ 63 ]

-

Pb(Mg 1/3 Nb 2/3 )O 3 -30PbTiO 3 Single-crystal

ceramic

190 6,500 [ 64 ]

Polyvinylidene fluoride Polymer 30 - 65 62 [ 65 ]

Poly(vinylidene fl uoride-tri fl u- Polymer 50 144 [ 66 ]

oroethylene) 60/40

a Temperature or temperature range where the pyroelectric coefcient was measured

The ceramic materials used for pyroelectric energy conversion applications are
mostly in the form of bulk materials with a thickness of around 100

ʼ

m. They

usually possess a large pyroelectric coef cient, and the most commonly used

ceramic pyroelectric material for energy harvesting is PbZr 0.95 Ti 0.05 O 3 (PZT). The
pyroelectric coef

cients of some ceramic materials are listed in Table 10.8 .
The polymer materials considered for pyroelectric energy harvesting are nor-
mally in the form of thick lms, with their thicknesses being a few tens of mi-

crometres. They possess a smaller pyroelectric coef cient in comparison with

ceramic materials, but they can be exposed to higher electric

elds before any
dielectric breakdown occurs and are considerably less expensive than ceramic
materials [ 61 ]. The most commonly used are polyvinylidene fl uoride (PVDF) lms

and their copolymers, such as poly(vinylidene fl uoride-tri fl uoroethylene) P(VDF-

TrFE). The pyroelectric properties of some polymer lms are presented in

Table 10.8 .
From Table 10.8 it is clear that some ceramics, for example the ( 0.67 Ba 0.33 Sr)
TiO 3 ceramic, possess a very large pyroelectric effect (7,000

cm − 2 K − 1 ). However,
it must be noted that such a high value is usually observed only in the vicinity of the
phase transition temperature and not over a broader temperature range [ 64 ].

µ

10.1.6 Review of Device Concepts and First Prototypes
for Pyroelectric Energy Harvesting

In order to harvest the electrical energy from the temperature uctuations of a

pyroelectric material, the material must be a part of a larger system where it
undergoes a thermodynamic cycle. Different solutions and ideas about how to
design such a system were proposed and are reviewed later in this chapter. In
addition, the

fl

rst prototype devices are presented. The chapter is divided into two
sections. In the rst section, the background behind the concepts of pyroelectric

energy harvesting devices is presented. In the second section, the experimental
realization of these concepts is reviewed.