Effect of phase transition on electrocaloric effect in Indium substituted BaTiO3 ceramics

Journal Pre-proof Effect of phase transition on electrocaloric effect in indium substituted BaTiO3 ceramics Y. Zhao, X.Q. Liu, S.Y. Wu, X.M. Chen PII:

S0925-8388(19)34878-9

DOI:

https://doi.org/10.1016/j.jallcom.2019.153632

Reference:

JALCOM 153632

To appear in:

Journal of Alloys and Compounds

Received Date: 21 November 2019 Revised Date:

30 December 2019

Accepted Date: 31 December 2019

Please cite this article as: Y. Zhao, X.Q. Liu, S.Y. Wu, X.M. Chen, Effect of phase transition on electrocaloric effect in indium substituted BaTiO3 ceramics, Journal of Alloys and Compounds (2020), doi: https://doi.org/10.1016/j.jallcom.2019.153632. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

Y.Z. performed the experiments and write the initial manuscript. X.Q. L. supervised the work. S.Y.W. performed part of the data analysis. X.M.C. directed the research work. All authors contributed to the discussion of the results and preparation of the manuscript.

Effect of Phase Transition on Electrocaloric Effect in Indium Substituted BaTiO3 Ceramics Y. Zhao, X.Q. Liu,* S.Y. Wu, and X.M. Chen Laboratory of Dielectric Materials, School of Materials Science and Engineering, Zhejiang University, No. 38 Zheda Road, Hangzhou 310027, China *Electronic mail: [email protected]

In the present work the dense Ba(Ti1-xInx)O3-x/2 ceramics were prepared through a standard solid-state sintering method. Although only a tetragonal phase is detected by the X-ray diffraction in these ceramics, the coexistence of multiphase is observed by the selected area electron diffraction in two substituted ceramics. Moreover, the diffused phase transition is induced by the substitution, and this can be linked to the coexistence of multiphase in these ceramics. The maximal pyroelectric coefficient of Ba(Ti0.99In0.01)O2.995 ceramics is obviously larger than those of the other ceramics, which occurs beside the ferroelectric-ferroelectric transition. While the maximal pyroelectric coefficients of other ceramics locate beside the paraelectric-ferroelectric transition. Ba(Ti0.99In0.01)O2.995 ceramics show the largest adiabatic temperature change of 0.54 K and isothermal entropy change of 0.94 J/kg·K under an electric field of 30 kV/cm among all ceramics, and the largest electrocaloric effect strengths of 0.22×10-6 K·m/V and 0.39×10-6 J·m/kg·K·V under an electric field of 10 kV/cm are also obtained in this ceramic. For individual composition, the electrocaloric strength displays different tendencies, which can be linked to the diffusivity of the phase transition. From the present work, the relationship between electrocaloric effect and ferroelectric phase transition is revealed.

Introduction In the polar materials, the electrocaloric effect (ECE) is defined as the adiabatic temperature and isothermal entropy by applying and removing the external electric field [1,2]. ECE can be used in solid-state refrigeration, and it is a promising candidate to replace traditional vapor-compression cooling technology. In 2006 giant ECE was found in PbZr0.95Ti0.05O3 thin film [3], lots of papers about ECEs are 1

published after this work [4-10]. Usually, adiabatic temperature change ∆T and isothermal entropy change ∆S are parameters to evaluate ECE, and they can be achieved through the Maxwell equation [11]. According to previously published work [12,13], ECE calculated through the Maxwell equation is reliable, an increasing number of papers about ECE calculated through the Maxwell equation are published [14-19]. The Maxwell equations are listed as following [20]: ∆T = − ∆S = −

( ) dE

(1)

( ) dE

(2)

Recently, the efficiency of electric field driving ECE is focused because of the limited household voltage [21-24], so there is a tendency to find materials with high ∆T and ∆S under a low electric field. To quantitatively evaluate this requirement, the concept of EC strength is introduced, which are defined as ∆T/∆E (adiabatic temperature change per electric field) and ∆S/∆E (isothermal entropy change per electric field), respectively. BaTiO3 is a typical material with perovskite structure, and the substitution of either Ba2+ or Ti4+ cations can tune the Curie temperature of the original material. As the number of substitution increases, three permittivity peaks come closer and get smoother, finally three peaks merge into one broaden peak, further substitution will cause the permittivity peak with frequency dispersion [25-27]. The ECE of the substituted BaTiO3 is directly linked to the variation of dielectric properties. A lot of papers about ECE of substituted BaTiO3 have been published [4,10,28-32], the influence of different characterizations such as relaxor phenomenon, invariant critical point and morphotropic phase boundary on ECE has been researched. Among these results, the substitutions of Ti4+ by Zr4+ or Sn4+ cations have been focused because of their superior ECEs [32-33].In these materials, the ionic radii of Zr4+(0.72 Å) and Sn4+(0.69 Å) are larger than that of Ti4+(0.605 Å) cation, and this may give some clues to improve the ECE. In present work, the larger In3+ cation (0.80 Å) is introduced, and the hetero-valent substituted Ba(Ti1-xInx)O3-x/2 ceramics were synthesized through a solid-state reaction method, the influence of the diffused phase transition on ECE is carefully investigated.

2

Experimental Procedure Ba(Ti1-xInx)O3-x/2 (x = 0.01, 0.03 and 0.05) ceramics were prepared by a standard solid-state reaction method. Powders of raw materials with high purity, i.e., BaCO3 (99.99%), TiO2 (99.99%) and In2O3 (99.99%) were weighed in stoichiometric ratio, ball mixed in alcohol and zirconia media for 24 hours and then dried. The mixtures was calcined at 1150 oC for 3h in air. After regrinding, calcined powders were added 5wt% PVA, then the mixture were compacted at 2 MPa for 1 minute into pellets. The pellets were calcined at 1400oC for 6 hours in the air. The crystal structures were identified using powder X-ray diffraction (XRD, RIGAKU D/max 2550/PC, Rigaku Co., Tokyo, Japan) at room temperature. The data for Rietveld refinement were collected at the 2θ range of 8 - 130o with a step of 0.02o. The Rietveld refinement was carried out using the Fullprof program [34]. The densities of samples were measured by Archimede method. The microstructures were evaluated on the thermal-etched surface by a scanning electron microscopy (SEM, S4800, Hitachi, Tokyo, Japan). Temperature dependence of dielectric permittivity was evaluated using a broad-band dielectric spectrometer (Turnkey Concept 50, Novocontrol Technologies GmbH & Co. KG, Hundsangen, Germany) with Au pasted. Electric polarization – electric field (P-E) hysteresis loops were measured at 10 Hz in the fixed temperature period using a Precision Analyzer (Precision Premier II, Radiant Technologies, Albuquerques, NM, USA) combined with a Sigma temperature controller. Heat capacity was measured using a differential scanning calorimeter (DSC, Netzsch DSC204 F1, Selb, Germany) apparatus. Samples for transmission electron microscopy (TEM) were prepared by mechanically grinding the ceramic pellets to a thickness of around 30 µm, and then breaking into small pieces. To reduce surface charging, a small piece of the sample was selected to attach to a copper ring with dimensions of 3 mm in outer and 0.8 mm in inner diameters. Then a final thinning was conducted via argon-ion milling. The selected area electron diffraction (SAED) patterns were obtained using a transmission electron microscopy (TEM, JEM-2100F, JEOL, Tokyo, Japan) at 200kV. Finally, the ECE was calculated via the Maxwell equation.

3

Results and Discussions The XRD patterns of Ba(Ti1-xInx)O3-x/2 ceramics are collected at room temperature, and the results are shown in Fig. 1. The Rietveld refinements are performed to identify the phase constitutes in these ceramics. A single P4mm phase is adopted for all ceramics based on the refinement results. Moreover, Table 1 shows the results in more detail. The parameter of c/a decreases with increasing the In3+ content because of the increasing cell parameter of a and unchanged cell parameter of c, and it is crucial to ferroelectric properties, such as Curie temperature. Fig. 1 also shows the microstructures of polished and thermal-etched surfaces for these ceramics. The wellarranged grains are observed in the dense ceramics, which is consistent with the high relative densities (> 97% of theoretical density). Additionally, the grain sizes of the ceramics decrease with the increasing the In3+ content. Although the single-phase has been observed in the Rietveld refinement of XRD patterns, a trace phase may not be determined because of the detective limitation of X-ray. To further investigate the structures of ceramics, Fig. 2 shows the SAED patterns for all ceramics. Fig. 2 (a) and (b) show the patterns along [110]T and [001]T zone axis for Ba(Ti0.99In0.01)O2.995 ceramics, respectively (here, the subscript of T indicates a tetragonal phase). It can be seen that only the tetragonal phase is observed in Ba(Ti0.99In0.01)O2.995 ceramics at room temperature, which is consistent with the result of XRD patterns. Fig. 2(c), (d) and (e) show the SAED patterns along [110]O, [010]O and [111]T zone axis for Ba(Ti0.97In0.03)O2.985 ceramics, respectively (here, the subscript of O indicates an orthorhombic phase). The coexistence of the tetragonal and orthorhombic phase is observed in Ba(Ti0.97In0.03)O2.985 ceramics. Fig. 2(f), (g), (h) and (i) show the SAED patterns along [111]C, [110]C, [111]T and [111]O zone axis for Ba(Ti0.95In0.05)O2.975 ceramics, respectively (here, the subscript of C indicates a cubic phase). It can be seen that the tetragonal, orthorhombic and cubic phases coexist in Ba(Ti0.95In0.05)O2.975 ceramics at room temperature. Although the crystal structure from the SAED pattern is different from that from the refinement of the XRD pattern, the result does not conflict since the former one is the local structure, while the latter one is the average structure. Moreover, the distribution of the secondary phase is rare in the TEM image.

4

The temperature dependences of relative dielectric permittivities of Ba(Ti1-xInx)O3x/2

ceramics at various frequencies are shown in Fig. 3(a), (b) and (c). No frequency

dispersion at the permittivity peak is observed in all ceramics, so the relaxor phenomenon can be excluded. It can be seen from the figure that, the permittivity peak becomes broader as the quantity of In3+ substitution increases, this is the typical phenomenon of diffused phase transition [35]. For Ba(Ti0.99In0.01)O2.995 ceramics, three permittivity peaks are observed on the curve. They are all induced from the phase transitions, that is, one is from paraelectric-ferroelectric and the other two are from ferroelectric-ferroelectric phase transitions, and this behavior is the same as that of pure BaTiO3 because of the small quantity of In3+ cations. For Ba(Ti0.97In0.03)O2.985 ceramics, two permittivity peaks are left because two ferroelectric-ferroelectric phase transitions merge into one. For Ba(Ti0.95In0.05)O2.975 ceramics, only one permittivity peak is found, which is corresponding to the paraelectric-ferroelectric phase transition. The influence of the substitution of In3+ cations on dielectric properties is a progressive procedure, and the quantity of x = 0.05 is just the critical point where the phase transition is diffusive but no relaxor phenomenon appears. To illustrate dielectric properties clearly, Fig. 3(d) displays the temperature dependence of relative permittivity at 1 MHz for all ceramics. The temperature of the tetragonalorthorhombic phase transition is about 298 K for Ba(Ti0.99In0.01)O2.995 ceramics, and that of paraelectric-ferroelectric phase transition is around 335 K for Ba(Ti0.95In0.03)O2.985 ceramics, while that of paraelectric-ferroelectric phase transition is about 307 K for Ba(Ti0.95In0.05)O2.975 ceramics. These temperatures are all around room temperature,

providing the convenience for ECE measurement and its applications because the largest ECE always locates beside the phase transition point. The inset of Fig. 3(d) shows the modified Curie-Weiss fitting of Ba(Ti1-xInx)O3-x/2 ceramics. It can be seen from the figure that the diffusivity coefficient of phase transition increases with the increasing In3+ content, i.e., the structural phase transition becomes more diffusive with increasing the In3+ content. This should be induced from the coexistence of tetragonal, orthorhombic and/or cubic phases in the ceramics [36], and this is consistent with the above-mentioned SAED results (see Fig. 2). In the present work, the ECE is calculated via the Maxwell equation. The temperature dependence of polarization should be extracted from P-E loops at various temperatures firstly, then the polynomial fitting will be applied to give the 5

pyroelectric coefficient. Fig. 4 shows P-E hysteresis loops of Ba(Ti1-xInx)O3-x/2 ceramics. One can see that the different shapes of hysteresis loops in different ceramics. For Ba(Ti0.99In0.01)O2.995 ceramics, the measuring temperature period locates beside the

tetragonal-orthorhombic ferroelectric phase transition, and the hysteresis loops indicate the typical ferroelectric phase with a rectangular shape and large remnant polarization. For Ba(Ti0.97In0.03)O2.985 ceramics, the measuring temperature period is just beside the paraelectric-ferroelectric phase transition point, and the hysteresis loops show the shapes between rectangular and slim shapes, implying that the material is transforming from paraelectric phase to ferroelectric phase. For Ba(Ti0.95In0.05)O2.975 ceramics, the measuring temperature period is just above the paraelectric-ferroelectric phase transition point, and the hysteresis loops show slim shape, which may be due to the characteristics of diffused phase transition. The maximal polarization values are extracted from the upper branches of the hysteresis loops, and the evolution of polarization with the temperature of Ba(Ti1-xInx)O3-x/2 ceramics is shown in Fig. 4. Then the fourth polynomial fitting is applied, and the fitting lines have no deviations with the evolutions of polarization with temperature (see the solid lines in Fig. 4). Then the fitted polynomial is deviated to achieve the pyroelectric coefficients (see Fig. 5). Finally, the ECE can be calculated from the Maxwell equation. The ECEs are mainly decided by the pyroelectric coefficients, so the varying tendency of the pyroelectric coefficients will directly influence the varying tendency of the ECEs. The largest pyroelectric coefficients are achieved at 10 kV/cm, 26 kV/cm and 36 kV/cm for x = 0.01, 0.03 and 0.05, respectively, which may be originated from the different mechanisms of the phase transitions (see Fig. 5). Obviously, the pyroelectric coefficient of Ba(Ti0.99In0.01)O2.995 ceramics is largest, which is induced from the ferroelectric-ferroelectric phase transition. While the coefficients of the other two ceramics are smaller, and they are obtained from the paraelectric-ferroelectric phase transitions. This result may give some clues to establish the relationship between the pyroelectric coefficient and the nature of the phase transition. Fig. 6 shows the adiabatic temperature change (∆T) and EC strength (∆T/∆E) of Ba(Ti1-xInx)O3-x/2

ceramics

at

various

temperatures.

Among

all

ceramics,

Ba(Ti0.99In0.01)O2.995 ceramics show the largest adiabatic temperature change (∆T) of 0.54 K under an electric field of 30 kV/cm, and the largest EC strength (∆T/∆E) of 0.22×10-6 K·m/V under an electric field of 10 kV/cm. The temperature dependence of 6

EC strength for Ba(Ti0.99In0.01)O2.995 ceramics shows the same varying tendency as its pyroelectric coefficient, that is, the EC strength monotonously decreases with the increasing the electric field. Ba(Ti0.97In0.03)O2.985 and Ba(Ti0.95In0.05)O2.975 ceramics show comparative EC strengths. The largest EC strength of Ba(Ti0.95In0.05)O2.975 ceramics is 0.12×10-6 K·m/V under an electric field of 36 kV/cm, while the largest EC strength of Ba(Ti0.97In0.03)O2.985 ceramics is 0.11×10-6 K·m/V under an electric field of 26 kV/cm. The temperature dependences of EC strength of Ba(Ti0.97In0.03)O2.985 and Ba(Ti0.95In0.05)O2.975 ceramics also show the same varying tendency as their pyroelectric coefficients. The EC strength firstly increases with increasing the electric field, and it will reach its largest values at a certain electric field, then it decreases. The measuring temperature period is just beside the paraelectric-ferroelectric phase transition, so it may need a large enough electric field to induce the phase transition, where the pyroelectric coefficient and EC strength achieve their largest values. Based on the results of ECEs for Ba(Ti0.97In0.03)O2.985 and Ba(Ti0.95In0.05)O2.975 ceramics, the electric field to drive the largest pyroelectric coefficient of Ba(Ti0.97In0.03)O2.985 ceramics is smaller than that of Ba(Ti0.95In0.05)O2.975 ceramics. The ECE is linked to the number of states [8,31,37-40], the number of states increases as the diffusivity of phase transition increases. A larger driving force may be needed to drive the transformation of more states, so it needs a larger electric field to drive the maximal pyroelectric coefficient in Ba(Ti0.95In0.05)O2.975 ceramics. Fig. 7 shows the temperature dependence of isothermal entropy change (∆S) and EC strength (∆S/∆E) of Ba(Ti1xInx)O3-x/2

ceramics. Among all ceramics, Ba(Ti0.99In0.01)O2.995 ceramics show the

largest isothermal entropy change 0.94 J/kg·K under an electric field of 30 kV/cm and the largest EC strength (∆S/∆E) of 0.39×10-6 J·m/kg·K·V under an electric field of 10 kV/cm. The largest EC strength (∆S/∆E) of Ba(Ti0.95In0.05)O2.975 ceramics is 0.19×10-6 J·m/kg·K·V under an electric field of 36kV/cm, and it for Ba(Ti0.97In0.03)O2.985 ceramics is 0.18×10-6 J·m/kg·K·V under an electric field of 26 kV/cm. The varying tendencies of EC strengths (∆S/∆E) of Ba(Ti1-xInx)O3-x/2 ceramics are just the same as those of the pyroelectric coefficients. Table 2 lists a comparison of ECEs between this work and published works, and it can be seen that the ∆T strength in this work is comparable to those of published works, certifying the significance of this work.

7

Conclusion Based on the Rietveld refinement of XRD patterns, only a tetragonal phase is observed in the ceramics. However, the coexistence of phases is found in Ba(Ti0.97In0.03)O2.985 and Ba(Ti0.95In0.05)O2.975 ceramics from the SAED patterns. The substitution of In3+ cations induces a diffused phase transition, and the diffusivity of phase

transition

increases

as

the

number

of

substitution

increases.

In

Ba(Ti0.99In0.01)O2.995 ceramics, the pyroelectric coefficient decreases as the electric field increases, while the maximal pyroelectric coefficients are achieved under an electric field of 26 kV/cm and 36 kV/cm for Ba(Ti0.97In0.03)O2.985 and Ba(Ti0.95In0.05)O2.975 ceramics, respectively. The electric field to drive the maximal pyroelectric coefficient of Ba(Ti0.95In0.05)O2.975 ceramics is larger than that of Ba(Ti0.97In0.03)O2.985 ceramics, and this should be linked to the number of the coexistent states. For Ba(Ti0.99In0.01)O2.995 ceramics, the largest adiabatic temperature change of 0.54 K and the isothermal entropy change of 0.94 J/kg·K are achieved under an electric field of 30 kV/cm among all ceramics, and the largest ECE strengths of 0.22×10-6 K·m/V (∆T/∆E) and 0.39×10-6 J·m/kg·K·V (∆S/∆E) are achieved under an electric field of 10 kV/cm around room temperature. Based on these results, although the type of phase transition (ferroelectric-ferroelectric or paraelectricferroelectric) has a dominated impact on the ECEs, the diffusivity of phase transition also can affect the ECEs in BaTiO3-based ceramics.

Acknowledgement This work was financially supported by the National Natural Science Foundation of China under Grant Nos. 51772266 and 51790493, the National Key R&D Program of China under Grant No. 2016YFA0300101, and Natural Science Foundation of Zhejiang Province under Grand No. LY20E020012.

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10

Table. 1 Rietveld results of XRD patterns of Ba(Ti1-xInx)O3-x/2 ceramics at room temperature.a) 0.01

0.03

0.05

a (Å)

4.00068(8)

4.01250(8)

4.01789(8)

c (Å)

4.02922(9)

4.02089(11)

4.02063(14)

1.0071

1.0021

1.0007

Volume (Å3)

64.489(2)

64.737(2)

64.907(3)

Ba Biso (Å2)

0.958(16)

0.730(19)

0.849(20)

Ti/Y z

0.5223(18)

0.5272(31)

0.4988(31)

Biso (Å2)

1.026(49)

0.701(87)

1.062(34)

O1 z

-0.005 (15)

-0.046 (5)

0.059(5)

O2 z

0.5349(34)

0.4430(46)

0.5745(47)

Rp (%)

7.99

8.53

7.14

Rwp (%)

10.7

11.2

9.86

χ2

5.88

5.19

6.40

x

c/a

a)

Space group: P4mm, Ba at 1a (0, 0, 0), Ti/In at 1b (0.5, 0.5, z), O1 at 1b (0.5, 0.5, z),

and O2 at 2c (0.5, 0, z).

11

Table. 2. Comparison of ECEs of different materials.

∆E (kV/cm) 10 26 36 12

∆T (K) 0.22 0.29 0.42 0.90

∆T/∆E(10-6 K·m/V) 0.22 0.11 0.12 0.75

∆S (J/kg·K) 0.39 0.46 0.67

∆S/∆E(10-6 J·m/kg·K·V) 0.39 0.18 0.19

T width (K) 8 8 8 4

Method

Ref.

Indirect Indirect Indirect Direct

This work This work This work Moya et al.6

Ba(Ti0.8Zr0.2)O3

T (K) ceramic 290 ceramic 324 ceramic 314 single 402 crystal ceramic 311

21

1.1

0.52

2.0

0.93

>30

Direct

Qian et al.32

Ba(Ti0.8Zr0.2)O3

ceramic 312

145

4.5

0.31

7.8

0.54

>30

Direct

Qian et al.32

Ba(Ti0.85Zr0.15)O3

ceramic 342

150

4.2

0.28

7.5

0.5

Direct

Qian et al.32

BZT-BCT BZT-BCT BCZT BCZT BNKT 0.99BT-0.01BMT 0.98BT-0.02BMT Ba0.65Sr0.35TiO3 BNT-0.06BT

ceramic ceramic ceramic ceramic ceramic ceramic ceramic ceramic ceramic

60 20 6.65 20 50 55 55 20 50

0.46 0.26 0.11 0.32 1.08 1.02 1.21 0.42 0.86

0.077 0.13 0.164 0.16 0.216 0.185 0.22 0.21 0.17

>30 20 15 20 15 20 20 20 20 15

Direct Indirect Indirect Direct Indirect Indirect Indirect Indirect Direct

Lu et al.41 Lu et al.41 Hanani et al.42 Weyland et al.43 Wang et al.44 Li et al.21 Li et al.21 Bai et al.45 Li et al.46

Material Ba(Ti0.99In0.01)O2.995 Ba(Ti0.99In0.03)O2.985 Ba(Ti0.99In0.05)O2.975 BaTiO3

Form

373 343 363 363 380 411 416 296 383

1.13 1.22

12

0.21 0.22

Fig. 1 Rietveld refinement results against XRD patterns and of SEM micrographs Ba(Ti1-xInx)O3-x/2 ceramics: (a) & (b) x = 0.01, (c) & (d) x = 0.03 and (e) & (f) x = 0.05.

13

Fig. 2 SAED patterns in (a) [110]T zone axis and (b) [001]T zone axis for Ba(Ti0.99In0.01)O2.995 ceramics, SAED patterns in (c) [110]O zone axis, (d) [010]O zone axis and (e) [111]T zone axis in Ba(Ti0.97In0.03)O2.985 ceramics, SAED patterns in (f) [111]C zone axis, (g) [110]C zone axis, (h) [111]T zone axis and (i) [111]O zone axis in Ba(Ti0.95In0.05)O2.975 ceramics.

14

16k

(a)

4k 0 100

200

16k (c)

εr'

12k 8k

8k

1 kHz 10 kHz 100 kHz 1 MHz

4k

300

400

500

Temperature(K)

0 100

600

16k 12k

1 kHz 10 kHz 100 kHz 1 MHz

8k

200

300

400

Temperature(K)

500

600

(d) -6 -8 -1 0 -1 2 -1 4 -1 6

γ (0.01) = 1.19 γ (0.03) = 1.42 γ (0.05) = 1.53

0

2

4

x = 0.01 x = 0.03 x = 0.05

6

ln(T-Tm ) (K)

4k

4k

0 100

1 kHz 10 kHz 100 kHz 1 MHz

εr'

8k

(b)

12k

εr'

εr'

12k

ln(1/ε-1/εm )

16k

200

300

400

500

600

Temperature(K)

0 100

200

300

400

500

600

Temperature(K)

Fig. 3 Temperature dependence of relative dielectric permittivity of Ba(Ti1-xInx)O3-x/2 ceramics at various frequencies: (a) x = 0.01, (b) x = 0.03 and (c) x = 0.05. (d) Temperature dependence of relative dielectric permittivity of Ba(Ti1-xInx)O3-x/2 ceramics at 1MHz. The inset is the modified Curie-Weiss fitting of Ba(Ti1-xInx)O3-x/2 ceramics.

15

0.20

(a)

10 2

P (C/m )

2

P (µC/cm )

20

0 297K 299K 301K

-10 -20 -30 -20

-10

0

10

20

0.15 10 kV/cm 14 kV/cm 20 kV/cm 26 kV/cm 30 kV/cm - fitted line

0.10

0.05

30

(b)

285

0.14

(c)

0 325K 327K 329K

-8 -16

300

305

310

(d)

0.12

-30 -20

-10

0

10

20

10kV/cm 14kV/cm 20kV/cm 26kV/cm 30kV/cm - fitted line

0.10 0.08

30

315

E (kV/cm) 12

0.12

(e)

320

325

330

Temperature (K)

335

(f)

0.09

2

P (C/m )

6

2

P (µC/cm )

295

2

P (C/m )

8

2

P (µC/cm )

16

290

Temperature (K)

E (kV/cm)

0 315K 317K 319K

-6 -12

-40 -30 -20 -10 0

0.06

0.03 305

10 20 30 40

E (kV/cm)

10kV/cm 16kV/cm 22kV/cm 28kV/cm 36kV/cm 40kV/cm - fitted line

310

315

320

325

Temperature (K)

Fig. 4 P-E hysteresis loops of Ba(Ti1-xInx)O3-x/2 ceramics: (a) x = 0.01, (c) x = 0.03 and (e) x = 0.05. Evolution of polarization with temperature of Ba(Ti1-xInx)O3-x/2 ceramics: (b) x = 0.01, (d) x = 0.03 and (f) x = 0.05. The lines are polynomial fitting results.

16

2

-1 10 kV/cm 14 kV/cm 20 kV/cm 26 kV/cm 30 kV/cm

-2

(b)

∂P/∂T (mC/m ⋅K)

2

∂P/∂T (mC/m ⋅K)

0

0.0

(a)

-0.4 10 kV/cm 14 kV/cm 20 kV/cm 26 kV/cm 30 kV/cm

-0.8

-1.2 315

280 285 290 295 300 305 310 315

320

Temperature (K)

330

335

340

0

(d)

2

-0.4

∂P/∂T (mC/m ⋅K)

2

∂P/∂T (mC/m ⋅K)

(c) 10 kV/cm 16 kV/cm 22 kV/cm 28 kV/cm 36 kV/cm 40 kV/cm

-0.8

-1.2 305

325

Temperature(K)

310

315

320

325

330

Temperature(K)

-1 x = 0.01 x = 0.03 x = 0.05

-2 290

300

310

320

330

Temperature(K)

Fig. 5 Pyroelectric coefficient of Ba(Ti1-xInx)O3-x/2 ceramics: (a) x = 0.01, (c) x = 0.03 and (e) x = 0.05. (d) The largest pyroelectric coefficient of each ceramic.

17

10kV/cm 14kV/cm 20kV/cm 26kV/cm 30kV/cm

(a)

-6

∆T (K)

0.4

∆T/∆E (10 K⋅m/V)

0.6

0.2 0.0 285

290

295

300

305

0.2

0.1

0.0 285

310

Temperature (K) 10kV/cm 14kV/cm 20kV/cm 26kV/cm 30kV/cm

(c)

300

305

310

0.12

10kV/cm 14kV/cm 20kV/cm 26kV/cm 30kV/cm

(d)

0.08

0.04

0.1 0.0

315

320

325

330

0.00

335

315

Temperature (K) 10kV/cm 16kV/cm 22kV/cm 28kV/cm 36kV/cm 40kV/cm

(e)

0.12

-6

0.3 0.2

325

330

335

10 kV/cm 16 kV/cm 22 kV/cm 28 kV/cm 36 kV/cm 40 kV/cm

(f)

0.08

0.04

0.1 0.0

320

Temperature (K) ∆T/∆E (10 K⋅m/V)

0.4

∆T (K)

295

-6

0.2

290

Temperature (K) ∆T/∆E (10 K⋅m/V)

∆T (K)

0.3

10kV/cm 14kV/cm 20kV/cm 26kV/cm 30kV/cm

(b)

305

310

315

320

325

330

305

Temperature (K)

310

315

320

325

330

Temperature (K)

Fig. 6 Temperature dependence of adiabatic temperature change (∆T) and EC strength (∆T/∆E) of Ba(Ti1-xInx)O3-x/2 ceramics, respectively: (a) & (b) x = 0.01, (c) & (d) x = 0.03 and (e) & (f) x = 0.05.

18

(a)

10 kV/cm 14 kV/cm 20 kV/cm 26 kV/cm 30 kV/cm

0.6 0.4

-6

∆S (J/kg⋅K)

0.8

∆S/∆E (10 J⋅m/kg⋅K⋅V)

1.0

0.2 0.0 285

290

295

300

305

310

0.5 0.4

(b)

0.3 0.2 0.1 0.0 285

10 kV/cm 14 kV/cm 20 kV/cm 26 kV/cm 30 kV/cm

0.4 0.3 0.2 0.1 315

0.16

300

305

(d)

310

10 kV/cm 14 kV/cm 20 kV/cm 26 kV/cm 30 kV/cm

0.12

320

325

330

335

0.08 0.04 315

0.8

(e)

10 kV/cm 16 kV/cm 22 kV/cm 28 kV/cm 36 kV/cm 40 kV/cm

0.6

325

330

335

0.20

(f)

10 kV/cm 16 kV/cm 22 kV/cm 28 kV/cm 36 kV/cm 40 kV/cm

0.16 0.12

-6

0.4 0.2 305

320

Temperature (K) ∆S/∆E (10 J⋅m/kg⋅K⋅V)

Temperature (K)

∆S (J/kg⋅K)

295

-6

∆S (J/kg⋅K)

(c)

290

Temperature (K) ∆S/∆E (10 J⋅m/kg⋅K⋅V)

Temperature (K) 0.5

10 kV/cm 14 kV/cm 20 kV/cm 26 kV/cm 30 kV/cm

310

315

320

325

0.08 0.04 305

Temperature (K)

310

315

320

325

Temperature (K)

Fig. 7 Temperature dependence of isothermal entropy change (∆S) and EC strength (∆S/∆E) of Ba(Ti1-xInx)O3-x/2 ceramics, respectively: (a) & (b) x = 0.01, (c) & (d) x = 0.03 and (e) & (f) x = 0.05.

19

Diffused phase transition has been observed in indium substituted BaTiO3 ceramics; The type of phase transition has a dominated impact on the electrocaloric effect; The diffusivity of phase transition can also affect the electrocaloric effect.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: