Alternative Caloric Energy Conversions - Magnetocaloric Energy Conversion: From Theory to Applications - page 399

could have advantages over bulk ceramics since a lower voltage is needed to induce
the electrocaloric effect. On the other hand, thin- lm ceramics can, in some cases,

exhibit a suf cient electrocaloric effect to be used in a cooling device without heat

regeneration. Because of their small thickness, thin- lm ceramics possess poor

mechanical properties. Furthermore, their thermal mass is very low. Therefore, they
should be processed in a multilayer structure that could improve their mechanical
properties and increase their thermal mass.

10.1.2.2 Electrocaloric Polymers

Polymers are a very interesting group of electrocaloric materials. They are mainly
polyvinylidene

fl uoride (PVDF)-based copolymers or terpolymers in the form of

thick m. They nor-

mally possess a very high dielectric strength, which can be as high as 350 MVm − 1 .
Therefore, the adiabatic temperature changes of polymer

lms with their thickness usually ranging between 1 and 15 ʼ

lms can be comparable to

those achieved in ceramic thin lms. For example, Li et al. [ 38 ] reported an adi-

abatic temperature change of 35 K measured in a 10-

lm. The
electrocaloric properties of some other polymers are presented in Table 10.4 .
Another favourable property of polymer

ʼ m-thick polymer

lms is that they are not as brittle as
ceramic materials. Furthermore, the large electrocaloric effect makes polymer-based
materials good material candidates for future electrocaloric devices. However, like
in the case of thick- and thin- lm ceramic materials, they should be further

Table 10.4 Electrocaloric properties of polymers
Material

a
(K)

Δ T ad
(K)

Δ s is
(Jkg − 1 K − 1 )

T ref Δ E

(MVm − 1 )

q r,max
(Jkg − 1 )

Measurement
procedure

References

P(VDF-TrFE 55/45) 12 70 340 120 23,380 Direct [ 39 ]

P(VDF-TrFE 68/32) 2.3 / 489 49 / Direct [ 12 ]

Irradiated P(VDF-TrFE
68/32)

20 95 306 160 28,120 Direct [ 31 ]

Irradiated P(VDF-TrFE
65/35)

35 160 323 180 48,880 Direct [ 38 ]

P(VDF-TrFE 70/30) 21.2 / 390 300 / Indirect [ 40 ]

P(VDF-TrFE-CFE)
(56.2/36.3/7.6)

21.6 / 350 350 / Indirect [ 40 ]

annealed P(VDF-TrFE-
CFE) (56.2/36.3/7.6)

9 47 318 300 14,735 Indirect [ 41 ]

quenched P(VDF-TrFE-
CFE) (56.2/36.3/7.6)

5 35 318 300 11,043 Indirect [ 41 ]

Terpolymer-copolymer
blend (90/10)

10 / 300 150 / Direct [ 42 ]

a T ref — temperature at which Δ T ad , Δ s is and q r,max were obtained