PST thin films for electrocaloric coolers

Abstract

Relaxor behaviour in a thin film of partially ordered PbSc 0.5 Ta 0.5 O 3 (PST) was confirmed via slim P-E loops and the frequency dependence of the temperature at which the dielectric constant is maximum. Indirect measurements of the electrocaloric effect suggest that removing a field of 774 kV cm-1 yields a temperature change of-3.5ºC to-6.9ºC over a broad range of operating temperatures near room temperature (1 ºC-127 ºC), with a correspondingly large refrigerant capacity of 662 J kg-1. In addition to low electrical hysteresis, there is negligible thermal hysteresis. PST thin films are therefore promising for EC cooling near room temperature.

The giant electrocaloric effect and high effective cooling power near room temperature for BaTiO3 thick film

“…Under an ultrahigh field of 800 kV/cm, the sample exhibits a giant electrocaloric effect of DT ¼ 7.1 K and DS ¼ 10.1 J/kg Á K at 80 C, 15 which exceeds the ECE value in most ferroelectric ceramics in previous reports. [5][6][7][8][9][10] Although the PbZr 0.95 Ti 0.05 O 3 thin film in Ref. 3 has higher ECE DT of $12 C, its DS of $8 J/kg Á K is smaller due to high operating temperature of 222 C. Because (1) large entropy change is more practical for the refrigerating application, (2) low working temperature would open up wider application prospect, and (3) large effective volume of multilayer thick film produces huger heat absorption capacity, the BaTiO 3 multilayer thick film has more promising application future.…”

“…Since 2006, the giant ECE (DT max > 5 K) was reported successively in various ferroelectric ceramics or polymer films, [3][4][5][6][7][8][9][10][11][12] where the ultrahigh applied field played a key role. Up to now, intense research and development efforts are still on-going and there are many blank, especially on the kinetics problem.…”

The electrocaloric effect around the orthorhombic- tetragonal first-order phase transition in BaTiO3

“…Although ECE research has been carried out for several decades, 1-3 the underlying physics behind ECE and its relation with phase transition are not yet completely understood. The thermodynamic theory based on the Maxwell relation was widely used in the characterization and analysis of ECE, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] but recent reports revealed that it is unsuitable for ferroelectric relaxors with non-ergodic glassy state 11,12 and becomes invalid near phase transitions 5,12 or under ultrahigh electric field, 14 which are two keys to achieve giant ECE. Since the origination of giant ECE has not been properly interpreted, the development of highly-efficient ferroelectric refrigeration is put off.…”

“…[1][2][3][4][5] Since 2006, a giant ECE with T = 5∼40K was subsequently observed in ferroelectric films under ultrahigh electric fields. [6][7][8][9][10][11][12][13][14] Although ECE T and/or S of thin films under high fields is much higher than that of bulk samples, the effect under unit field is weakened significantly, 4 about one order of magnitude (from 0.2∼1.0K · m/MV to 0.01∼0.1K · m/MV). In this paper, we quantitatively distinguish the dominant factor of ECE near a phase transition, and achieve a large effect of T/E = 1.4K · m/MV in BaTiO 3 near room temperature (RT).…”

“…8 This was not experimentally confirmed previously, because the discontinuity of thermodynamic characters, especially the order parameter of polarization P, makes the theoretical calculation invalid to predict the ECE near a first-order phase transition. 12,20,21 The inhomogeneity and defects in real materials will induce the energy fluctuation, so the potential barrier of lattices is has a distribution, not an identical value. Considering the phase transition only occurs in the lattices with potential barrier lower than the applied field, no further phase transition is induced lattices under a same field, unless the applied field is further enhanced.…”