Alternative Caloric Energy Conversions - Magnetocaloric Energy Conversion: From Theory to Applications - page 397

10.1.2.1 Electrocaloric Ceramic Materials

Ceramic materials exhibiting the electrocaloric effect can be, based on their
thickness, divided into bulk ceramics (with a thickness greater than 100 µ m), thick-

lm ceramics (with a thickness of a few tens of micrometres) and thin- lm ceramics

(with a thickness of less than 1 µ m). Such a classi cation is also common in other

areas where electroceramics are used [ 14 ].
The adiabatic temperature change in bulk ceramics is usually of the order of a
few kelvins, as can be seen from Table 10.1 . The highest adiabatic temperature
change of a bulk ceramic material known to the authors of this topic was 4.5 K for
the Ba(Zr 0.2 Ti 0.8 )O 3 (BZT) ceramic [ 15 ].
Thick- 100 times thinner than bulk ceramics. In

most cases they are in the form of a multilayer structure, also known as a multilayer
capacitor. The largest electrocaloric effect in a multilayer capacitor was reported by
Bai et al. [ 24 ]. They measured an adiabatic temperature change of 7.1 K in a multi-
layer capacitor constructed from 63 layers of 3-

lm ceramics are, in general, 10

-

m-thick BaTiO 3 . Kar-Narayan et al.
[ 25 , 26 ] measured the adiabatic temperature change of a very similar, commercially
available, multilayer structure; however, they reported an adiabatic temperature
change of 0.5 K. Furthermore, Kar-Narayna et al. [ 27 ] analysed the cooling powers
achievable withmultilayer capacitors. Based on theoretical estimations they predicted
that an idealized electrocaloric cooling device with multilayer capacitors could
achieve a speci

ʼ

c cooling power up to 2,875 Wkg − 1 . One of the few cases where the
electrocaloric effect was measured in a thick-

lm ceramic that was not in the form of a

multilayer capacitor was reported by Ro ž i č et al. [ 12 ]. They measured an adiabatic

temperature change of 1.8 K in a 28- ʼ m-thick PLZT 8/65/35 ceramic lm. The

electrocaloric properties of some thick- lm ceramics are collected in Table 10.2 .

Table 10.1 Electrocaloric properties of bulk ceramics
Material

a
(K)

Δ E (MVm − 1 ) q r,max
(Jkg − 1 )

Δ T ad
(K)

Δ s is
(Jkg − 1 K − 1 )

T ref Measurement

procedure

References

BNT-0.3BT 2.1 / 423 5 / Indirect [ 16 ]

−

BNT-KN 1.73 / 349 1.7 / Indirect [ 17 ]

BZT (x = 0.2) 4.5 8 312 14.5 2,478 Direct [ 15 ]

BZT (x = 0.15) 4.2 7.3 342 15 2,481 Direct [ 15 ]

NBT − 0.34 − 0.43 413 5 176 Indirect [ 18 ]

NBT-0.08BT 0.19 0.26 370 4 96 Indirect [ 18 ]

PLZT 8/65/35 2.2 / 385 8.8 / Direct [ 19 ]

PMN 2.6 / 451 9 / Direct [ 12 ]

PMN 0.11 / 274 1 / Indirect [ 20 ]

PMN-0.85PT 1.7 / 291 1.6 / Direct [ 21 ]

PMN-0.3PT 2.7 / 429 9 / Direct [ 19 ]

PMN-0.08PT 1.3 / 296 1.5 / Direct [ 22 ]

PZN-0.08PT 0.25 / 453 1.2 / Direct [ 23 ]

a T ref

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