THETHE GIANT ELECTROCALORIC EFFECT: phenomenon for applicationGIANT ELECTROCALORIC EFFECT: phenomenon for applicationTHETHE GIANT ELECTROCALORIC EFFECT: phenomenon for application GIANT ELECTROCALORIC EFFECT: phenomenon for application in cooling and heating devices of new generationin cooling and heating devices of new generationg g gg g g

Brigita Rožič prof matBrigita Rožič, prof. mat.Jožef Stefan International Postgraduate School, Nanosciences and NanotechnologiesJožef Stefan International Postgraduate School, Nanosciences and Nanotechnologies

MENTOR: prof dr Zdravko KutnjakMENTOR: prof. dr. Zdravko KutnjakCO AUTHORS d B b M lič d H U šič d J H l d M ij KCO-AUTHORS: dr. Barbara Malič, dr. Hana Uršič, dr. Janez Holc, dr. Marija Kosec,

d R š Pi d R b Blidr. Raša Pirc, dr. Robert BlincJ ž f S f I i J 39 1000 Lj blj Sl iAb t tAb t t Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, SloveniaAbstractAbstract

Electrocaloric effect (ECE) is a change in the temperature of material due to electric field under adiabatic conditions, and it generates great interest due to its application, forexample in electrical refrigeration. A giant electrocaloric effect was observed in inorganic ferroelectrics [1]. These observations were based on the indirect measurements ofthe electrical polarization. We show direct measurements of ECE in PMN, PMN-30 PT, PMN-35 PT and in PLZT 8/65/35 ceramics. Both bulk samples and thin films werethe electrical polarization. We show direct measurements of ECE in PMN, PMN 30 PT, PMN 35 PT and in PLZT 8/65/35 ceramics. Both bulk samples and thin films weremeasured. The temperature dependence reveals that the maximum of ECE is obtained at the ferroelectric phase transition. The magnitude of ECE shows that the giant ECE

b l f d i diff l f l f l ican be easly found in different classes of relaxor ferroelectrics.

El l i “C ”Electrocaloric cooling cycle

“Compressor”cooling cycle

GIANT ELECTROCALORIC EFFECT Electrocaloric cooling cycle is comparable with acorresponding cooling cycle of a classic compressorwhere pressure p of the gas is changing.

cooling/heating devicesapplication

• simple design ffi i

p g

• no moving parts•more energy efficient

f i dli f iThe electrocaloric device:

g p • friendlier for environment

ExprimentalExprimental methodmethod SAMPLESSAMPLESpp SAMPLESSAMPLES

thick film of PMN-35PT35PT

Direct electrocaloric measurements i hi h l i l i

Measurement:

5 mm≈70 μm thick420150

•step electrical signal used

via high resolution calorimeter

Produced by

μ

419120

Tb th

•step electrical signal used

ΔT l l t d f fit ty

J. Holc, H. Uršič, M. Kosec, JSI418

90

T [K

]

V/c

m)

Tbath •ΔT calculated from fits tothe exponentially decaying

i

A simple diagram of the systemof sample and calorimeter A

bulk of PMN-35PT60 80 thi k

5 mm

thin film of PLZT ceramics417

60T

E (k

V wingsof sample and calorimeter. Asample is coupled to a bath andth i t b th th l 60-80 μm thick

416

0

30 •resistive heating alsotaken into account

thermistor by the thermalconductances.

Produced by J. Holc, M. Kosec, JSI

0 50 100 150 200 250 300 3500

t [s]

5 mm ≈200 nm thick

Produced by B. Malič, M. Kosec, JSIDirect measurements of the giant electrocaloric effectDirect measurements of the giant electrocaloric effectgg

bulk PMN-30PT ceramics bulk PMN ceramics

bulk PMN-30PT ceramicsE[kV/cm]

2.5[ V ]

2 5

2.5 bulk PMN ceramicsE [kV/cm]

8 4

THICK FILMS2.0 7.5

3060

2.0 8.4 25.552 6

1.5

[K]

60 90 1.5

Κ]

52.6 90THIN FILMSTHIN FILMS

1.0 ΔT

[

1.0

ΔΤ [Κ

THIN FILMSTHIN FILMS

0.5 0 5

0 0

0.5

thin films of PLZT ceramics320 340 360 380 400 420

0.0

220 240 260 280 300 320 340

0.0thin films of PLZT ceramics

T [K] 220 240 260 280 300 320 340T [K]

408/65/35 PLZT thin film

C l iC l i

40 at 318 K

ConclusionConclusion30

We can conclude that direct measurements confirmi t f th i t l t l i ff t i diff t

30

K) 3,0x10-7 PMN ceramics

PLZT 8/65/35existence of the giant electrocaloric effect in differentclasses of relaxor ferroelectrics. The largest electrocaloric20

ΔT (K

8 ts)

V)

PLZT 8/65/35 SRBRF modelclasses of relaxor ferroelectrics. The largest electrocaloric

effect is observable in thin PLZT films.

Δ

2,0x10-78

y un

i

K m

/V

iti l10

7 trary

/E (K

criticalpoint

01,0x10-7

3x10-7

4x10-74

(arb

i

ΔT/E

0 500 1000 15000

E (kV/cm) 1 10-7

2x10-7

T/E

(

PMN-30PT ceramics

criticalpoint

E (kV/cm) 0,0

0 4 8 12 160

1x100 ΔTceramics

ΔT/E as a function of the maximum of the amplitudeof the electric-field pulses (in units of ECP) in bulk

ReferenceReferencess 0,0 0,5 1,0 1,5 2,0 2,5E/E

of the electric field pulses (in units of ECP) in bulkPMN, 8/65/35 PLZT and PMN-30PT ceramics (insetwith same axis labels) Solid red line represents resultsReferenceReferencess

[1] A.S. Mischenko, Q. Zhang, J.F. Scott, R.W. Whatmore, N.D. Mathur, Science 311,E/ECP

with same axis labels). Solid red line represents resultsof calculations of ΔT/E based on on a SRBRF model[2]1270 (2006).

[2] B. Rožič, Sheng-Guo Lu, Z. Kutnjak, B. Malič, H. Uršič, J. Holc, M. Kosec, R. Pirc,[2].

R. Blinc, B. Neese, M. Lin, E. Furman, Q. M. Zhang (poslano v objavo, 2010)