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Direct Measurement of Large Electrocaloric Effect in Ba(ZrxTi1-x)O3 Ceramics xiaodong Jian, Biao Lu, Dandan Li, Yingbang Yao, Tao Tao, Bo Liang, Jin-Hong Guo, Yi-Jiang Zeng, Jia-Le Chen, and Sheng-Guo Lu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b15933 • Publication Date (Web): 12 Jan 2018 Downloaded from http://pubs.acs.org on January 12, 2018

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ACS Applied Materials & Interfaces

Direct Measurement of Large Electrocaloric Effect in Ba(Zr xTi1-x)O3 Ceramics Xiao-Dong Jian, Biao Lu, Dan-Dan Li, Ying-Bang Yao, Tao Tao, Bo Liang, Jin-Hong Guo, Yi-Jiang Zeng, Jia-Le Chen and Sheng-Guo Lu∗

(Guangdong Provincial Research Center on Smart Materials and Energy Conversion Devices, Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter, School of Materials and Energy, Guangdong University of Technology, Guangzhou, 510006, China) *Author to whom any correspondence should be addressed. Electronic mails: [email protected]. (S. G. Lu)

Abstract Barium zirconate titanate (Ba(ZrxTi1-x)O3) ceramics with Zr4+ content x of 5, 10, 15, 20, 25 and 30 mol%, were prepared using a solid-state-reaction approach. The microstructures, morphologies, and electric properties were characterized using XRD, SEM and impedance analysis methods, respectively. The dielectric analyses indicate that the BZT bulk ceramics show characteristics of phase transition from a normal ferroelectric to a relaxor ferroelectric with the increasing Zr4+ ionic content. The electrocaloric effect (ECE) adiabatic temperature change decreases with the increasing Zr4+ content. The highest adiabatic temperature change obtained is 2.4 K for BZT ceramics with a 5 mol% of Zr4+ ionic content.

Keywords: barium zirconate titanate, ceramics, dielectric properties, phase transition, electrocaloric effect

1. Introduction Electrocaloric effect (ECE), as an inverse of pyroelectric effect, is induced by the change of polarization states when the external electric field is applied/removed to a ∗

Electronic mail: [email protected]

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polar material under the adiabatic condition. ECE has attracted increasing interest from researchers around the world since the giant ECEs have been reported in ferroelectric/antiferroelectric ceramic thin films, single crystals and polymers recently, which demonstrate the potential of being used in the solid-state refrigeration (1-5). Compared with the conventional vapor-compression refrigerator, ECE refrigerator is a more efficient energy conversion approach with high energy conversion efficiency over 60% of the Carnot cycle (under the assumption that the ECE temperature change is 2 K) (6) and environment-friendly alternative to overcome the disadvantage of using gaseous refrigerants by the vapor-compression refrigerators. In addition, compared with the magnetocaloric solid-state refrigerator, which is another solid-state cooling technology, the big sized magnet is a drawback for the refrigerators (7). As a result, the solid-state cooling device can be downsized drastically, which is beneficial for the application in cooling the microelectronic chips. However, the challenge in the design of solid-state cooling devices is the selection of the ECE materials. Ferroelectrics and/or antiferroelectrics are regarded as two categories of the promising candidates that are easy to find out their giant electrocaloric effects due to the large polarization and the structural transition driven by the temperature as well as the electrical field. Since Mischenko et al. reported a large adiabatic temperature change of ∆T=12 K at 499 K under an external electric field of 48 MV·m -1 for Pb(ZrTi)O3 (PZT) thin films in 2006 (8), various giant ECE performances were reported in various compositions of ferroelectric and antiferroelectric materials. For example, for ceramic bulks, ∆T=2.7 K and │∆T·∆E-1│=0.3 K·MV -1 at 492 K under 9 MV·m -1 in PMN-0.3PT, and ∆T= 2.2 K at 385 K under 9 MV·m-1 were obtained in PLZT 8/65/35 in 2011 reported by Rozic et al. (9). Secondly, for ceramic films, Bai et al presented ∆T=7.1 K and at 333 K under 80 MV·m-1 in BaTiO3 (BTO) multilayer ceramic capacitors (MLCC) (10). And the even larger ∆T around 40 K at 318 K was procured under an applied electric field of 120 MV·m-1 in (PbLa)(ZrTi)O3 (PLZT) 8/65/35 thin films by Lu et al (11). Furthermore, because of the high breakdown electrical fields, ferroelectric polymer materials have been investigated extensively (12). For instance, a ∆T=21.6 K was obtained in poly(vinylidene fluoride – trifluoroethylene – chlorofluoroethylene) 2


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(P(VDF-TrFE-CFE)) (56.2/36.3/7.6) terpolymers at 350 K and an electric field of E=350 MV·m-1 (13). And a ∆T=12 K and ∆S=70 J·kg-1·K-1 were procured in poly(vinylidene fluoride – trifluoroethylene) (P(VDF-TrFE)) (55/45) copolymers at 340 K and an external electric field of 120 MV·m-1 reported by Lu et al. (14). BTO is a basic material with a strong polarity, i.e. high permittivity, low loss tangent, large

polarization

and

big

adiabatic

temperature

change

(∆T)

(14),

and

environment-friendly. However, the Curie temperature in BTO system approaches 120 ℃ (15), which is far from the room temperature that will be one of the disadvantages for commercialization of ECE devices that they are designed to preferably work at room temperature. Doping is an effective way to modify the BTO system, for instances, to shift the Curie temperature to room temperature, to enhance the ECE at room temperature, Zr4+ (14-18), Sr4+(19), Ca4+(20-22, 27), Sn4+(23-25), Hf3+(26, 27), Ce4+(28, 29) and other ionic elements with similar electronegativity are chosen to dope into the BTO system. Among them, Zr4+ ions were chosen in this work due to its ionic radius (0.72 Å) which is similar to Ti4+ (0.605 Å), wider sintering conditions, environment friendly, and transition properties of normal ferroelectric to relaxor ferroelectric (30). For a normal ferroelectric with a second-order phase transition, and approximately for a relaxor ferroelectric, the Maxwell relation (shown in Eq. (1)) can be used to calculate the ECE values (Eqs. (2) and (3)) (31,32). ࣔࡼ

ࣔࡿ

ቀ ቁ =ቀ ቁ ࣔࢀ ࣔࡱ ࡱ

ࡱ

∆‫ = ܂‬− ‫ ࡱ׬‬૛

૚

ࣔࡼ

ቀ ቁ ࢊࡱ

(2)

࣋࡯ࡱ ࣔࢀ ࡱ૛ ࣔࡼ ‫ ࡱ׬‬ቀࣔࢀ ቁ ࢊࡱ ૚ ૚

∆‫= ܁‬

(1)

ࢀ

(3)

where P, E, S, and T are the polarization, electrical field, entropy and temperature, ࡯ࡱ is the specific heat capacity and ρ is the density, ∆T is the adiabatic temperature change, and ∆S is the isothermal entropy change, which are the characteristic parameters to illustrate the ECE of a material. However, Eqs. (1), (2) and (3) can be applicable for materials with the second-order phase transition and the first-order phase transition above the Curie temperature. For materials with the first-order phase transition, the polarization versus temperature is 3



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discontinuous at the phase transition temperature, then the Clausius-Clapeyron equation should be used instead (32, 33). For relaxor ferroelectrics, due to non-ergodicity issue at certain temperature regions, Equations (1), (2) and (3) cannot be used. However, since the polarization as a function of temperature is continuous, the Maxwell relation can be applicable approximately in some temperature range that is ergodic for relaxor ferroelectrics. In this work, BaZrxTi1-xO3 bulk ceramics were prepared using a solid-state process. The structural and electrical properties were characterized. Direct and indirect measurements on ECEs were carried out.

2. Experimental A series of BaZrxTi1-xO3 ceramics with x=5, 10, 15, 20, 25, and 30 mol% were prepared using a solid-state-reaction method. Raw materials used were BaCO3 (purity ≥ 99.0 %, Aladdin ), ZrO2 (purity ≥ 99.0 %, Aladdin ) and TiO2 (purity ≥ 99.0 %, Aladdin ). The batch materials were weighed according to the stoichiometry, and ball milled at 256 rpm for 24 h using a planetary miller. The milled slurry was dried at 65 °C for 6 h. Then the mixed powders were ground, sieved and calcined at 1300 ~ 1325 °C for 4 h to form the perovskite crystallites. Then the Ba(ZrxTi 1-x)O3 crystallized powders were mixed with 20 wt% PVB, sieved, and

pressed into pellets with 1.2 cm in

diameter and 1 mm in thickness under an axial pressure of 3 MPa and an isostatic pressure of 250 MPa, respectively. Then the green samples were sintered at the temperatures ranging from 1325 °C to 1400 °C for 120 min in order to achieve the densification. Both sides of the ceramic were polished and sputtered gold as electrodes for electrical measurements. X-ray diffraction (XRD) measurement (Rigaku Ultima Ⅳ) was carried out at room temperature, using Ni-filtered CuKα radiation (λ=1.5406 Å) with a scanning step of 0.08° with a counting time of 1 s per step, from 20° to 80°. Scanning electron microscope (Hitachi SU3400) coupled with energy dispersive X-ray spectroscopy was employed to observe the morphologies of the samples. The relative densities of BZT bulk ceramics were calculated in terms of the ratio of the specific density measured using Archimedes’ 4


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method and the theoretical density which was estimated from the XRD data. Dielectric constants as a function of frequency and temperature were obtained using the Precision Impendence Analyzer (Agilent 4284A). The polarization – electric field (P-E) hysteresis loops as a function of temperature and electric field, were measured using a RADIANT Trek

Model

609B

standard

ferroelectric

analysis

system.

The

electrocaloric

characteristics including thermal response in this study were directly procured by a specially designed calorimeter with a thermometer. Results were compared with the calculated values based on the Maxwell relations (shown in Eqs. (1) ~ (3) using the polarizations extracted from the P-E hysteresis loops procured at various temperatures and electric fields. The ECE adiabatic temperature changes (∆T) and isothermal entropy change (∆S) were obtained using the equation Cv⋅∆T=-T⋅∆S.

3. Results and discussion 3.1 XRD analysis The XRD patterns of BZT bulk ceramics at compositions of x=5, 10, 15, 20, 25 and 30 mol% at room temperature were shown in Fig. 1 (a). The diffraction peaks show a pure perovskite structure without any impurities. The diffraction peaks were shifted towards lower angles with the increase of Zr4+ ionic content due to the replacement of Ti4+ ions by Zr4+ ions which have a bigger ionic radius (0.72 Å, Ti4+ ionic radius 0.605 Å). The peaks from 43° to 46° of XRD patterns of all BZT bulk ceramic samples were magnified and shown in Fig. 1 (b), which reveals that the diffraction peak (002) gets weaker and the peak (200) becomes stronger with the increase of Zr4+ ions, indicating the transformation from a normal ferroelectric to a relaxor ferroelectric at room temperature. For BZT 5%-doped sample, there are two peaks ((200) and (002)) appeared near 45° and the c/a ratio calculated is 1.006, which suggests the tetragonal structure at room temperature, and its space group is P4mm. With the increase of Zr4+ ionic content, the c/a ratio approaches 1.000, which means a pseudo-cubic structure at room temperature, and its space group changes into Pm3m.

3.2 SEM observation 5



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Figure 2 shows the SEM images of BZT bulk ceramics which contain different Zr4+ contents, and were sintered at temperatures ranging from 1325 °C to 1400 °C for 120 min. The relative densities are higher than 97%, obtained using the Archimedes’ method. Results indicate that the dense ceramic structures and distinct grain boundaries were formed under the above sintering conditions. Meanwhile, crystalline grains with 2~7 µm in size, which were obtained by adjusting the preparation conditions, are considered to be one of the main factors in affecting the electric properties, i.e., permittivity, polarization, and breakdown electric field. It has been verified that the lattice constants and domain structures are associated with the grain size (33, 34).

3.3 Dielectric characteristics The incorporation of Zr4+ ions to BaTiO3, which will enter into the B-site in ABO3 structure, will remarkably affect the dielectric properties, e.g., Curie temperature (Tm), transition of normal ferroelectric to relaxor ferroelectric, broadening of phase transition from paraelectric to ferroelectric phases. The permittivities as a function of temperature and frequency are shown in Figs. 3 (a) – (c). Higher permittivity (Ɛr~18500@ 1 kHz at Tm with 15 mol% of Zr4+ ions) and lower loss tangent (8 % @ 1 kHz) were obtained. With the increase of Zr4+ ionic element, the Curie temperature (Tm) shifts from 103°C for Sample Zr-5% to -45°C for Sample Zr-30% towards lower temperatures. In the meantime, Tm peaks become broader and shift to the high temperatures with the increasing frequency when the Zr4+ ionic content increases. Figure 3 (b) reveals the permittivities as a function of temperature and frequency for 5%-Zr4+ doped BZT bulk ceramics. TO-T is the temperature at which the structural phase transforms from an orthorhombic to a tetragonal phase at ~55°C, it shifts towards high temperatures and merges with the Curie temperature which decreases with the increase of Zr4+ ionic content. In addition, the BZT system transforms from normal ferroelectrics with a first-order phase transition (Zr4+ content ≤ 10%) to relaxor ferroelectrics as shown in Fig. 3 (c) due to the Zr4+ ionic doping in BTO perovskite structure. It is because that when the Zr4+ ions are doped, the different ionic radii lead to the distortion of the octahedral, and also the change of

6


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ferroelectric domain sizes, which was confirmed in Ba(SnTi)O3 ceramics doped with different Sn4+ ionic contents (24, 35, 36). 3.4 Polarization-electric field (P-E) hysteresis loop The P-E loops for series of BZT bulk ceramics with doped Zr4+ ions with (a) 5 mol%, (b) 10 mol %, (c) 15 mol %, (d)

mol 20%, (e) 25 mol%, and (f) 30 mol%, were

measured under an external electric field of 5 MV·m-1 at 20 °C and 100 °C and 10 Hz, and shown in Fig. 4. The P-E loops reveal a normal ferroelectric hysteresis loop with the polarization of 25.70 µC·cm-2 for 5%-Zr4+ doped BZT bulk ceramic at 20℃ and 5 MV·m-1. With the increasing of Zr4+ ionic content, Pmax decreases, and the P-E hysteresis loops become slimmer and slimmer, until an approximately linear form. However, at temperatures near or higher than 100 °C, the thermal ions make contribution to the electric conduction, resulting in the increase of loss tangent, thus the P-E loop becomes a little fatter.

3.5 Electrocaloric effect (ECE) The adiabatic temperature change (∆T), defined in Eq. (2), is used to characterize the ECE occurred in BZT ceramics. Two approaches were employed to procure the ∆T, one is called indirect method, which uses the Maxwell relations and the polarizations extracted from the P-E loops at various temperatures and electric fields; another is called direct method, which uses the thermocouple to measure the temperature change when an external electric field is applied to the ceramic sample in an adiabatic condition. The actual measurement system is illustrated below. A T-type thermocouple was directly contact the ceramic sample using a kapton tape to measure the temperature change. A thermistor was adhered to the ceramic sample and used to measure the temperature of the sample. The whole sample plus the thermocouple and the thermistor was input a plastic bag to form an approximately adiabatic environment to reduce the heat dissipation. A high voltage amplified by the power amplifier was also connected with the sample using a Cu conductive paste. The signal generated from the thermocouple was amplified by the preamplifier and input to the computer. The application of the electric field and the measurement of the temperature change were well controlled and recorded 7



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by the computer. The corresponding results are shown in Fig. 5 (a) and Figs. S-1 – S-5 in the Supporting Information. Figure 5 (b) and Figs S-1-S-5 (b) in the Supporting Information show the adiabatic temperature changes (∆T) for 5, 10, 15, 20, 25, and 30 mol%-doped BZT bulk ceramics via the direct and indirect methods. The maximum values obtained via a direct method for BZT bulk ceramics decline from 2.4 K (5%-doped BZT, 113 °C, 3 MV·m-1) to 1.24 K (30%-doped BZT, 103 °C, 3 MV·m -1) with the increasing Zr4+ ionic content. For 5%-doped BZT, the curve shows the discontinuity of ∆T and the maximum value of direct measurement, ∆T=2.4 K at 113 °C, which is close to the Curie temperature of the ceramic (Tc=103 °C) at 3 MV·m -1. It was observed that the ECE temperature change decreases with the increasing Zr4+ ionic content, which is consistent with the decrease of polarization with the Zr4+ ionic content. The reason might be due to the change of ferroelectric domain size reduces with the increasing Zr4+ ionic content. This needs further confirmation of the microstructural characterization. Compared with the directly measured ECE results, indirectly calculated values based on the Maxwell relations are smaller, which are shown in Fig. 5, and Figs. S-1-S-5 (b) in the Supporting Information. For BZT ceramics with higher Zr4+ ionic contents, the phase transition around the peak permittivity is from a relaxor ferroelectric to a paraelectric phase. As did by Smolensky for relaxor ferroelectrics (37), a statistical model should be adopted to illustrate the permittivity – temperature relationships because the nanosized domains are distributed throughout the polycrystalline ceramic, resulting in the compositional fluctuation, which leads to the polarization versus temperature behaves close to but different from that of the second-order phase transition. Thus the Maxwell relation can be approximately used for relaxor ferroelectrics. For BZT ceramics with lower Zr4+ ionic contents, the phase transitions are of first-order, in which the

Maxwell

relations

cannot

be

applied,

the

Clausius-Clapeyron

equation

(∆S/∆E=∆P/∆T) should be added to Eqs. (2) and (3) instead. Moreover, the direct ECE measurement is for all the polarizations existed in the ceramics, while for P-E loop measurement, only the polarizations along the electric field direction can be recorded, thus the calculation of ECE from the Maxwell relation will be definitely smaller than 8


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those obtained from the direct measurement (38). In addition, it is well known that the ECE depends on two parameters, one is the phenomenological coefficient of P2 in the elastic Gibbs free energy expression. This coefficient is associated with the Curie constant, representing the correlation of polar domains in relaxor ferroelectrics, or polar dipoles in general. In relaxor ferroelectrics, the correlation among the polar nano regions is weak, then the Curie constant is usually smaller than that of the normal ferroelectrics, thus the phenomenological coefficient is larger than that of normal ferroelectrics, hence the relaxor ferroelectrics have a larger ECE. This is consistent with the equation obtained by Pirc (39), in which the ECE is proportional to lnΩ, where Ω is the states existed in the material. Since the BZT has more states at the multiphase point, i.e., x=0.15, it is possible that the composition has a larger ECE. Our results indicated that there is a small peak near the multiphase point, which proves that the states have an impact on the ECE. However, there is another parameter affecting the ECE, i.e., polarization. Since the entropy change is also proportional to the P2, thus the polarization plays a more important role in affecting the ECE. This is why the first-order phase transition material has a larger ECE. Here, because the BZT ceramic with x=0.05 closes to the BaTiO3 in physical properties, especially in the phase transition, therefore it has a larger ECE. Table 1 presents the directly measured results of ECEs in various electrocaloric materials, e.g., single crystals, disc ceramics, MLCCs, thick/thin films, and polymers. Although high ∆T values are achieved in those PbTiO3-based thin films and polymers, e.g., PLZT (11), P(VDF-TrFE) (40) and P(VDF-TrFE-CFE) (41), the excellent ECE properties can only be obtained under an extremely high external electric field, e.g., above 120 MV·m -1. In addition, Pb2+ ions in Pb2+ containing materials are detrimental to the environment. The BTO-based ceramics seem a better choice for ECE cooling devices. However, ∆T =0.9 K in BTO single crystal is not big enough (42), and the giant ECEs are usually obtained at high temperatures (~ 120 °C) which is not convenient for commercial applications. Fortunately, doping is an effective way to modify the electric properties of materials with a perovskite structure, e.g., the enhancement of the breakdown electric field. It has been reported that a ∆T of 4.5 K was achieved at 14.5 9



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MV·m-1 and 39 °C in Ba(Zr0.2Ti0.8)O3 glass modified ceramics (14). The glass doping, however, will reduce the ferroelectricity as well as the polarization. Thus, in this work, BZT ceramics with 5, 10, 15, 20, 25, and 30 mol% of Zr4+ content, are prepared and the ECE was investigated. Larger ECE responses (∆T ≥ 1.1 K for all compositions and ∆Tmax= 2.4 K for 5% BZT) under a relatively low electric field of 3 MV·m-1 are obtained. Moreover, a ECE efficiency (│ΔT·∆E-1│) of 0.8 K·MV⋅m -1 was procured for 5% BZT, which is among the largest values reported thus far (43, 44).

4 Conclusions In conclusion, barium zirconate titanate ceramics with 5, 10, 15, 20, 25 and 30 mol% of Zr4+ ionic contents, were prepared using a solid-state-reaction approach. The permittivities as a function of temperature and frequency show the characteristics changed from a normal ferroelectric to a relaxor ferroelectric with the increasing Zr4+ ionic content. The highest adiabatic temperature change obtained is 2.4 K with a 5 mol% doped BZT. Furthermore, the ECE values obtained via a direct measurement are larger than those derived via the calculation using the Maxwell relations and the polarization extracted from the P-E hysteresis loops.

Supporting Information The direct ECE measurement results for BZT ceramics with Zr4+ content of 10, 15, 20, 25 and 30 mol% are summarized in the Supporting Information. ACKNOWLEDGEMENTS This work was supported by the Natural Science Foundation of China (Grant No. 51372042), the Guangdong Provincial Natural Science Foundation (2015A030308004), and the NSFC-Guangdong Joint Fund (Grant No. U1501246).

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(20) Kaddoussi, H.; Lahmar, A.; Gagou, Y.; Asbani, B.; Dellis, J. L.; Cordoyiannis, G.; Allouche, B.; Khemakhem, H.; Kutnjak, Z.; El Marssi, M. Indirect and direct electrocaloric measurements of (Ba1− x Cax)(Zr0.1Ti0.9)O3 ceramics (x= 0.05, x= 0.20). J. Alloy. Compd. 2016, 667, 198-203. (21) Asbani, B.; Dellis, J. L.; Lahmar, A.; Courty, M.; Amjoud, M.; Gagou, Y.; Djellab, K.; Mezzane, D.; Kutnjak, Z.; El Marssi, M. Lead-free Ba0.8Ca0.2(ZrxTi1−x)O3 ceramics 12


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with large electrocaloric effect. Appl. Phys. Lett. 2015, 106, 042902. (22) Xue, D.; Gao, J.; Zhou, Y.; Ding, X.; Sun, J.; Lookman, T.; Ren, X. Phase transitions and phase diagram of Ba (Zr0.2Ti0.8)O3-x (Ba0.7Ca0.3)TiO3 Pb-free system by an elastic measurement. J. Appl. Phys. 2015, 117, 124107. (23) Upadhyay, S. K.; Reddy, V, R.; Bag, P.; Rawat, R.; Gupta, S. M.; Gupta, A. Electro-caloric effect in lead-free Sn doped BaTiO3 ceramics at room temperature and low applied fields. Appl. Phys. Lett. 2014, 105, 112907. (24) Lu, S. G.; Xu, Z. K.; Chen, H. Tunability and relaxor properties of ferroelectric barium stannate titanate ceramics. Appl. Phys. Lett. 2004, 85, 5319-5321. (25) Horchidan, N.; Ianculescu, A. C.; Curecheriu, L. P.; Tudorache, F.; Musteata, V.; Stoleriu, S.; Dragan, N.; Crisan, D.; Tascu, S.; Mitoseriu, L. Preparation and characterization of barium titanate stannate solid solutions. J Alloy Compd. 2011, 509, 4731-4737. (26) Li, J.; Zhang, D.; Qin, S.; Li, T. Y.; Wu, M.; Wang, D.; Bai, Y.; Lou, X. J. Large room-temperature electrocaloric effect in lead-free BaHfxTi1− x O3 ceramics under low electric field. Acta. Mater. 2016, 115, 58-67. (27) Zhao, C.; Wu, W.; Wang, H.; Wu, J. Site engineering and polarization characteristics in (Ba1− y Ca y)(Ti1− x Hf x) O3 lead-free ceramics. J. Appl. Phys. 2016, 119, 024108. (28) Srikanth, K. S.; Vaish, R.; Enhanced electrocaloric, pyroelectric and energy storage performance of BaCexTi1−xO3 ceramics. J Eur Ceram Soc. 2017, 37, 3927-3933. (29) Xie, S.; Bai, Y.; Han, F.; Qin, S.; Li, J.; Qiao, L.; Guo, D. Distinct effects of Ce doping in A or B sites on the electrocaloric effect of BaTiO3 ceramics. J. Alloy. Compd. 2017, 724, 163-168. (30) Kleemann, W., Miga, S., Dec, J., and Zhai, J. Crossover from ferroelectric to relaxor and cluster glass in BaTi1-xZrxO3 (x=0.25-0.35) studied by non-linear permittivity. Appl. Phys. Lett. 2013, 102, 232907. (31) Rožič, B.; Malič, B.; Uršič, H.; Holc, J.; Kosec, M.; Neese, B.; Zhang, Q. M.; Kutnjak, Z. Direct measurements of the giant electrocaloric effect in soft and solid ferroelectric materials. Ferroelectrics. 2010, 405, 26-31. (32) Lu, S. G.; Rožič, B.; Zhang, Q. M.; Kutnjak, Z.; Pirc, R.; Lin, M. R.; Li, X. Y.; 13



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Gorny, L. Comparison of directly and indirectly measured electrocaloric effect in relaxor ferroelectric polymers. Appl. Phys. Lett. 2010, 97, 202901. (33) Cai, W.; Fu, C.; Gao, J.; Chen, H. Effects of grain size on domain structure and ferroelectric properties of barium zirconate titanate ceramics. J. Alloy. Compd. 2009, 480, 870-873. (34) Wang, X. H.; Chen, R. Z.; Gui, Z. L.; Li, L. T. The grain size effect on dielectric properties of BaTiO3 based ceramics. Mat. Sci. Eng. B-Solid, 2003, 99, 199-202. (35) Wei, X.; Feng, Y.; Yao, X. Dielectric relaxation behavior in barium stannate titanate ferroelectric ceramics with diffused phase transition. Appl. Phys. Lett. 2003, 83, 2031-2033. (36) Wei, X.; Feng, Y.; Yao, X. Slow relaxation of field-induced piezoelectric resonance in paraelectric barium stannate titanate. Appl. Phys. Lett. 2004, 84, 1534-1536. (37) Smolensky, G. A. Physical phenomena in ferroelectrics with diffused phase transition. J. Phys. Soc. Jpn, 1970, 28, 26-37. (38) Lu, B.; Li, P.; Tang, Z.; Yao, Y.; Gao, X.; Kleemann, W.; Lu, S. G. Large electrocaloric effect in relaxor ferroelectric and antiferroelectric lanthanum doped lead zirconate titanate ceramics. Sci Reps, 2017, 7, 45335. (39) Pirc R, Kutnjak Z, Blinc R, et al. Upper bounds on the electrocaloric effect in polar solids[J]. Applied Physics Letters, 2011, 98(2): 021909. (40) Li, X.; Qian, X. S.; Gu, H.; Chen, X. Z.; Lu, S. G.; Lin, M. R.; Bateman, F.; Zhang, Q. M. Giant electrocaloric effect in ferroelectric poly (vinylidenefluoride trifluoroethylene) copolymers near a first-order ferroelectric transition. Appl. Phys. Lett. 2012, 101, 132903. (41) Li, X.; Qian, X.; Lu, S. G.; Cheng, J.; Fang, Z.; Zhang, Q. M. Tunable temperature dependence of electrocaloric effect in ferroelectric relaxor poly (vinylidene fluoride – trifluoroethylene – chlorofluoroethylene) terpolymer. Appl. Phys. Lett. 2011, 99, 052907. (42) Moya, X.; Stern‐Taulats, E.; Crossley, S.; González‐Alonso, D.; Kar‐Narayan, S.; Planes, A.; Mathur, N. D. Giant Electrocaloric Strength in Single‐Crystal BaTiO3. Adv. Mater. 2013, 25, 1360-1365. (43) Bai, Y.; Zheng, G.; Shi, S. Direct measurement of giant electrocaloric effect in 14


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BaTiO3 multilayer thick film structure beyond theoretical prediction. Appl. Phys. Lett. 2010, 96, 192902. (44) Kar-Narayan, S.; Mathur, N. D. Direct and indirect electrocaloric measurements using multilayer capacitors. J. Phys. D-Appl. Phys., 2010, 43, 032002.

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Figure captions Fig. 1 X-ray diffraction patterns of (a) BZT bulk ceramics, and (b) magnified patterns from 43° to 48°. Fig. 2 SEM images of BZT bulk ceramics sintered at temperatures ranging from 1325 ℃ to 1400 ℃ for 120 min. Fig. 3 The permittivities as a function of temperature and frequency for all compositions of BZT bulk ceramics (a), for Ba(Zr0.05Ti0.95)O3 bulk ceramics (b), and for Ba(Zr0.3Ti0.7)O3 bulk ceramics (c). Fig. 4 The P-E loops measured under an external electric field of 5 MV·m-1 at 10 Hz for BZT bulk ceramics with Zr4+ ionic content, (a) 5, (b) 10, (c) 15, (d) 20, (e) 25, (f) 30 mol%, respectively. Fig. 5 （a）Polarization as a function of temperature extracted from P-E loops shown in Fig. 4 (a) at the external electric field of 1, 2, and 3 MV·m-1; (b) direct measurement of ∆T for Ba(Zr0.05Ti0.95)O3 bulk ceramic under an external electric field of 3 MV·m-1 and indirect calculation via the Maxwell relations for Ba(Zr0.05Ti0.95)O3 bulk ceramic under the external electric field of 1, 2, and 3 MV·m-1 ; (c-f) directly measured ∆T as a function of time for Ba(Zr0.05Ti0.95)O3 bulk ceramic under an external electric field of 3 MV·m-1 at different temperatures.

16


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Table of Contents Graphic The application and removal of an external electric field to a polar material will induce the phase transition and reject and absorb heat.

17



Fig. 1 X-ray diffusion patterns of (a) BZT bulk ceramics, and (b) magnified patterns from 43° to 48°. 258x98mm (300 x 300 DPI)


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Fig. 2 SEM images of BZT bulk ceramics sintered at temperatures ranging from 1325 ℃ to 1400 ℃ for 120 min. 457x213mm (300 x 300 DPI)



Fig. 3 The permittivities as a function of temperature and frequency for all compositions of BZT bulk ceramics (a), for Ba(Zr0.05Ti0.95)O3 bulk ceramics (b), and for Ba(Zr0.3Ti0.7)O3 bulk ceramics (c). 125x263mm (300 x 300 DPI)


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Fig. 4 The P-E loops measured under an external electric field of 5 MV•m-1 at 10 Hz for BZT bulk ceramics with Zr4+ ionic content, (a) 5, (b) 10, (c) 15, (d) 20, (e) 25, (f) 30 mol%, respectively. 135x63mm (300 x 300 DPI)



Fig. 5 （a）Polarization as a function of temperature extracted from P-E loops shown in Fig. 4 (a) at the external electric field of 1, 2, and 3 MV•m-1; (b) direct measurement of ∆T for Ba(Zr0.05Ti0.95)O3 bulk ceramic under an external electric field of 3 MV•m-1 and indirect calculation via the Maxwell relations for Ba(Zr0.05Ti0.95)O3 bulk ceramic under the external electric field of 1, 2, and 3 MV•m-1 ; (c-f) directly measured ∆T as a function of time for Ba(Zr0.05Ti0.95)O3 bulk ceramic under an external electric field of 3 MV•m-1 at different temperatures. 269x188mm (300 x 300 DPI)


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Table 1 Comparison of ECE values for different types of materials Material

Form

T(℃)

∆T(℃)

∆E(MV·m-1 )

∆T·∆E -1 (k·m·MV -1 )

Method

Reference

Ba(Zr0.05 Ti 0.95 )O3

bulk

113

2.4

3

0.8

Direct

This work

Ba(Zr0.1 Ti0.9 )O3

bulk

83

1.7

3

0.56

Direct

This work

Ba(Zr0.15 Ti 0.85 )O3

bulk

61

1.2

3

0.4

Direct

This work

Ba(Zr0.2 Ti0.8 )O3

bulk

37

1.21

3

0.4

Direct

This work

Ba(Zr0.25 Ti 0.75 )O3

bulk

25

1.1

3

0.37

Direct

This work

Ba(Zr0.3 Ti0.7 )O3

bulk

28

1.18

3

0.39

Direct

This work

BTO

single crystal

129

0.9

1.2

0.75

Direct

[34]

BTO

ceramic MLCC

96

7.1

80

0.09

DSC

[10]

BTO

ceramic MLCC

80

1.8

17.6

0.1

DSC

[35]

Doped-BTO

ceramic MLCC

21

0.5

30

0.02

Direct

[36]

Ba(Zr0.2Ti0.8)O3

ceramics-glass

39

4.5

14.5

0.31

Direct

[14]

PLZT

thin film

45

40

120

0.33

Direct

[11]

P(VDF-TrFE)

polymer

33

35

180

0.13

Direct

[37]

P(VDF-TrFE-CFE)

polymer

30

15.7

150

0.1

Direct

[38]



TOC 190x121mm (300 x 300 DPI)


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Direct Measurement of Large Electrocaloric Effect ... - ACS Publications

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