**2. Experimental procedure**

PLZT(7/65/35) and PLZT(9.1/65/35) ceramics and BaTiO3 ceramics were used for ECE meas‐ urement. PLZT(7/65/35) and PLZT(9.1/65/35) ceramics were sintered from the commercial powders (Hayashi Chemical) as starting materials. BaTiO3 ceramics were sintered from the commercial powders (Toda Kogyo). The powders were fired at 1225–1275°C for PLZT ceramics at 1300–1400°C for BaTiO3 ceramics, respectively [20-22].

The ceramics were polished and then produced electrodes using a silver paste. And the ceramics were polarized for 20 min in a silicone bath under a DC field of 20 kV/cm at room temperature. The dielectric constant and tanδ were measured at 1 kHz with an oscillating

**Figure 1.** The merits of ECE cooler.

considered to be one of the new cooling mechanisms [1, 3, 4]. By using ECE, the application to compact a high energy-effective, inexpensive, and safe refrigerator would be considered, as shown in Fig. 1. ECE was discovered in 1930 by Kobeko and Kurchakov [5]. The research activities on ECE have been not active until the year 2006. In that year, "giant" temperature change in Pb(Zr,TiO3 (PZT) thin films were activated at one sweep [6]. Figure 2 shows the relation between the numbers of the published papers and the published year. After 2006, the number of papers on ECE increased rapidly [7-17]. The operation principle of the refrigerator using ECE is shown in Fig. 3. By applying the electric field, the ferroelectrics are heated by ECE. This process corresponds to the compression process in the compressor type refrigerator. By removing the electric field, the directions of the polarization become random. This process is endothermic, corresponds to the expansion process in the compressor type refrigerator, and the object is cooled. The electrocaloric effect (ECE) is a phenomenon in which a material shows a reversible temperature change under an applied electric field. In order to create ECE cooling devices, materials with large ECEs are required. The electrocaloric temperature change ∆T due

> 2 1

*C T* æ ö ¶ D =- ç ÷

*T P dE*

Here, C and *ρ* are the specific heat and density, respectively. Based on equation (1), a large (∂P/ ∂T)<sup>E</sup> (i.e., a large polarization change with temperature under high electric field) is desirable. With respect to achieving large (∂P/∂T)E, relaxor materials have recently attracted attention [1, 3, 4]. For direct measurement of the ∆T, there are some difficulties. Most temperature changes are less than 1K. And heat dissipation from ferroelectric materials through electrode, wire, and/or the supporting jig for field application occurs. Most probably due to these difficulties, the reports on the direct measurement of ∆T are limited thus far [13, 17, 18]. In this study, the electrocaloric temperature change, ∆T, due to applied ∆E, of the PLZT ceramics and BaTiO3 ceramics is estimated and directly measured. Concerning direct measurement of temperature– electric field (T–E) hysteresis loops, the reports have been limited. Detailed measurements of

*E*

è ø ¶ ò (1)

*E E*

r

various measurements are required to clarify the insights of the ECE [4, 18, 19, 20].

PLZT(7/65/35) and PLZT(9.1/65/35) ceramics and BaTiO3 ceramics were used for ECE meas‐ urement. PLZT(7/65/35) and PLZT(9.1/65/35) ceramics were sintered from the commercial powders (Hayashi Chemical) as starting materials. BaTiO3 ceramics were sintered from the commercial powders (Toda Kogyo). The powders were fired at 1225–1275°C for PLZT ceramics

The ceramics were polished and then produced electrodes using a silver paste. And the ceramics were polarized for 20 min in a silicone bath under a DC field of 20 kV/cm at room temperature. The dielectric constant and tanδ were measured at 1 kHz with an oscillating

to applied ∆E is calculated from the following equation [6]:

**2. Experimental procedure**

140 Advanced Ceramic Processing

at 1300–1400°C for BaTiO3 ceramics, respectively [20-22].

T

**Figure 2.** Year to year comparison of the numbers of papers on ECE, 1958-2014.

voltage of 1 V. An alternating electric field of 0.1 Hz was used in these measurements. The dielectric constant was measured using an Agilent Technology impedance analyzer, 4192A. Piezoelectric d33 meter (IACAS ZJ-3B) was used for piezoelectric measurements. Polarization–

**Figure 3.** The operation mechanism of the ECE cooler.

electric field (P–E) hysteresis loops of the samples at various temperatures were measured using a combination of a programmable signal generator and a charge amplifier (POEL 101). The samples were cut into 3–4 mm squares, and their temperatures were changed by immers‐ ing them in a heated or a cooled oil bath [21,22]. Strain–electric field (s–E) hysteresis loops of the samples at room temperature were measured using a combination of a programmable signal generator and a strain gauge. Triangular waves of 0.1 Hz with 30 kV/cm were applied to the samples in P–E and s–E measurements. The sample temperatures during the application of triangular waves of 0.1 Hz with 30kV/cm field were measured using a platinum thermom‐ eter. The sample temperatures changed periodically in accordance with the external field. The polarization reversals of the samples were monitored on the basis of signals from the charge amplifier (POEL 101). By synchronization of electric field to sample temperature, temperature– electric field (T–E) hysteresis loops were obtained.
