Electrocaloric Effect of Lead-free Bulk Ceramics: Current Status and Challenges

doi:10.15541/jim20190308

Abstract

Abstract:

Solid-state cooling technology based on the electrocaloric (EC) effect is attracting increasing attention as an important alternative for traditional cooling systems because of its advantages of high efficiency, environmental friendliness, light weight, low cost, and easy miniaturization. Ferroelectric materials are suitable candidates for EC refrigeration due to their large polarization and entropy change through applying or removing an external electric field. Recently, study on the EC effect of lead-free bulk ceramics has become one of hot topics on ferroelectric community due to the requirements of sustainable development. In this review, we firstly introduce the significant history events in EC research and the basic principles of EC refrigeration. Then, design strategy for achieving a large EC temperature change near room temperature and a wide using range is summarized. Subsequently, we systematically review the research status of EC effect in BaTiO₃-based, Bi_0.5Na_0.5TiO₃-based and K_0.5Na_0.5NbO₃-based lead-free bulk ceramics and discuss their advantages as well as challenges. Finally, we propose some prospects for the future work on EC effect in lead-free bulk ceramics.

Key words: lead-free bulk ceramics, electrocaloric effect, dielectric breakdown strength, phase transition, review

CLC Number:

TB64

YU Ying, DU Hongliang, YANG Zetian, JIN Li, QU Shaobo. Electrocaloric Effect of Lead-free Bulk Ceramics: Current Status and Challenges[J]. Journal of Inorganic Materials, 2020, 35(6): 633-646.

Figures/Tables 8

Fig. 1 The influence of changing electric field to polarization states of a ferroelectric (a), publication numbers on Web of Science database from 2000 to 2018 (b) and structure of the review (c) Theme searching of (b): “electrocaloric effect”, “electrocaloric effect” and “bulk ceramic”, “electrocaloric effect” and “thin film”, “electrocaloric effect” and “polymer”, “electrocaloric effect”, and “thick film”

Fig. 2 Historical development course of EC effect[5,16,33-36,53,59]

Fig. 3 A solid-state EC cooling device and working mechanism of P(VDF-TrFE-CFE) cooling device to move heat from heat source to heat sink by electrostatic actuation[59]

Fig. 4 Schematic diagram of impact factors on electrical breakdown

Fig. 5 Schematic diagram of composition design for achieving a large ?T near room temperature and a wide using range FE: ferroelectric; AE: antiferroelectric; PE: paraelectric

Fig. 6 Schematic diagram of composition design of BT based ceramics

Fig. 7 The relationship between ΔT and temperature of different types BT based ceramics under 15-40 kV/cm[50-52,63,65,67,89-98,101]

Fig. 8 The EC properties of BT, BNT and KNN based lead-free bulk ceramics[50-52,63-65,67,74, 89-98,101,107,108,110-118,121-126] (a) ΔT and temperature; (b) ΔT and electric field; (c) ΔT/ΔE and temperature; (d) ΔT/ΔE and electric field

References 130

[1]	SHI J Y, HAN D L, LI Z C , et al. Electrocaloric cooling materials and devices for zero-global-warming-potential, high-efficiency refrigeration. Joule, 2019,3:1-26. DOI URL
[2]	SUCHANECK G, GERLACH G . Lead-free relaxor ferroelectrics for electrocaloric cooling. Materials Today: Proceedings, 2016,3(2):622-631.
[3]	CORREIA T, ZHANG Q . Electrocaloric Materials: New Generation of Coolers. Berlin: Spinger, 2014: 1-3.
[4]	DU G, LIANG R H, LI T , et al. Recent progress on defect dipoles characteristics in piezoelectric materials. Journal of Inorganic Materials, 2013,28(2):123-130. DOI URL
[5]	MISCHENKO A S, ZHANG Q, SCOTT J F , et al. Giant electrocaloric effect in thin-film PbZr_0.95Ti_0.05O₃. Science, 2006,311(5765):1270-1271. DOI URL
[6]	ZHANG G Z, ZHANG X S, YANG T N , et al. Colossal room-temperature electrocaloric effect in ferroelectric polymer nanocomposites using nanostructured barium strontium titanates. ACS Nano, 2015,9(7):7164-7174. DOI URL
[7]	ZHANG G Z, LI Q, GU H M , et al. Ferroelectric polymer nanocomposites for room temperature electrocaloric refrigeration. Adv. Mater., 2015,27(8):1450-1454.
[8]	WANG D, CHEN X, YUAN G L , et al. Toward artificial intelligent self-cooling electronic skins: large electrocaloric effect in all-inorganic flexible thin films at room temperature. J. Materiomics, 2019,5(1):66-72. DOI URL
[9]	DARBANIYAN F, DAYAL K, LIU L P , et al. Designing soft pyroelectric and electrocaloric materials using electrets. Soft Matter., 2019,15(2):262-277. DOI URL
[10]	LI Q, ZHANG G Z, ZHAN X S , et al. Relaxor ferroelectric-based electrocaloric polymer nanocomposites with a broad operating temperature range and high cooling energy. Adv. Mater., 2015,27(13):2236-2241. DOI URL
[11]	KLEIN L, APARICIO M, JITIANU A . Handbook of Sol-Gel Science and Technology: Processing, Characterization and Applications. 2nd ed. Springer: Switzerland, 2018: 667-693.
[12]	BAI Y, WEI D, QIAO L J. Control multiple electrocaloric effect peak in Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ by phase composition and crystal orientation. Appl. Phys. Lett., 2015, 107(19): 192904-1-4.
[13]	YE H J, QIAN X S, JEONG D Y , et al. Giant electrocaloric effect in BaZr_0.2Ti_0.8O₃ thick film. Appl. Phys. Lett., 2014, 105(15): 152908-1-4.
[14]	LI F, CHEN G R, LIU X , et al. Type-I pseudo-first-order phase transition induced electrocaloric effect in lead-free Bi_0.5Na_0.5TiO₃- 0.06BaTiO₃ ceramics. Appl. Phys. Lett., 2017, 110(18): 182904-1-5.
[15]	VALANT M, AXELSSON A K, LE GOUPIL F , et al. Electrocaloric temperature change constrained by the dielectric strength. Mater. Chem. Phys., 2012,136(2/3):277-280. DOI URL
[16]	NEESE B, CHU B J, LU S G , et al. Large electrocaloric effect in ferroelectric polymers near room temperature. Science, 2008,321(5890):821-823. DOI URL
[17]	ZHANG G Z, WENG L X, HU Z Y , et al. Nanoconfinement-induced giant electrocaloric effect in ferroelectric polymer nanowire array integrated with aluminum oxide membrane to exhibit record cooling power density. Adv. Mater., 2019, 31(8): 1806642-1-8.
[18]	ZHUO F P, LI Q, GAO J H, et al. Coexistence of multiple positive and negative electrocaloric responses in (Pb, La)(Zr, Sn, Ti)O₃ single crystal. Appl. Phys. Lett., 2016, 108(8): 082904-1-5.
[19]	KUTNJAK Z ROŽIČ B, PIRC R , Wiley Encyclopedia of Electrical and Electronics Engineering (John Wiley& Sons)., 2015: 1-19.
[20]	LIU Y, SCOTT J F, DKHIL B. Direct and indirect measurements on electrocaloric effect: recent developments and perspectives. Appl. Phys. Rev., 2016, 3(3): 031102-1-18.
[21]	LI X Y, LU S G, CHEN X Z , et al. Pyroelectric and electrocaloric materials. J. Mater. Chem. C, 2013,1:23-37. DOI URL
[22]	VALANT M . Electrocaloric materials for future solid-state refrigeration technologies. Prog. Mater Sci., 2012,57(6):980-1009. DOI URL
[23]	LIU Y, SCOTT J F, DKHIL B. Some strategies for improving caloric responses with ferroelectrics. APL Mater., 2016, 4(6): 064109-1-9.
[24]	SINYAVSKY Y V, BRODYANSKY V M . Experimental testing of electrocaloric cooling with transparent ferroelectric ceramic as a working body. Ferroelectrics, 1992,131(1):321-325. DOI URL
[25]	CAZORLA C . In the search of new electrocaloric materials: fast ion conductors. Results Phys., 2015,5:262-263. DOI URL
[26]	SCOTT J F . Electrocaloric materials. Annu. Rev. Mater. Res., 2011,41:229-240. DOI URL
[27]	FÄHLER S, RÖßLER U K, KASTNER O , et al. Caloric effects in ferroic materials: new concepts for cooling. Adv. Eng. Mater., 2012,14(1/2):10-19. DOI URL
[28]	MANOSA L, PLANES A, ACET M . Advanced materials for solid-state refrigeration. J. Mater. Chem. A, 2013,1(16):4925-4936. DOI URL
[29]	LU S G, TANG X G, WU S H , et al. Large electrocaloric effect in ferroelectric materials. Journal of Inorganic Materials, 2014,29(1):6-12. DOI URL
[30]	ALPAY S P, MANTESE J, TROLIER-MCKINSTRY S , et al. Next-generation electrocaloric and pyroelectric materials for solid-state electrothermal energy interconversion. MRS Bull., 2014,39(12):1099-1111. DOI URL
[31]	MOYA X, KAR-NARAYAN S, MATHUR N D . Caloric materials near ferroic phase transitions. Nat. Mater., 2014,13:439-450. DOI URL
[32]	BAI Y, LI J T, QIN S Q , et al. Ferroelectric ceramics for high-efficient solid-state refrigeration. Advanced Ceramics, 2018,39(6):369-389.
[33]	THOMSON W, KELVIN L. On the thermoelastic, thermomagnetic, and pyroelectric properties of matter. Phil. Mag., 1878,5(28):4-27.
[34]	KOBEKO P, KURTSCHATOV J . Dielektrische eigenschaften der seignettesalzkristalle. Z. Phys., 1930,66(3/4):192-205.
[35]	HAUTZENLAUB J F . Electrocaloric and Dielectric Behavior of Potassium Dihydrogen Phosphate. Massachusetts: Massachusetts Institute of Technology Doctoral Dissertation, 1943.
[36]	RADEBAUGH R, LAWLESS W N, SIEGWARTH J D , et al. Feasibility of electrocaloric refrigeration for the 4-15 K temperature range. Cryogenics, 1979,19(4):187-208. DOI URL
[37]	KIMURA T, NEWNHAM R E, CROSS L E . Shape-memory effect in PLZT ferroelectric ceramics. Phase Transit., 1981,2(2):113-130. DOI URL
[38]	BIRKS E, SHEBANOV L, STERNBERG A . Electrocaloric effect in PLZT ceramics. Ferroelectrics, 1986,69(1):125-129. DOI URL
[39]	LAWLESS W N . Specific heat and electrocaloric properties of KTaO₃ at low temperatures. Phys. Rev. B, 1977,16(1):433-439. DOI URL
[40]	SINYAVSKY Y V, PASHKOV N D, GOROVOY Y M , et al. The optical ferroelectric ceramic as working body for electrocaloric refrigeration. Ferroelectrics, 1989,90(1):213-217. DOI URL
[41]	XIAO D Q, YANG B, PENG S Q , et al. Analyses and syntheses of ferroelectric refrigeration ceramics. Ferroelectrics, 1997,195(1):93-96. DOI URL
[42]	ZHAO Y, HAO X H, ZHANG Q . A giant electrocaloric effect of Pb_0.97La_0.02(Zr_0.75Sn_0.18Ti_0.07)O₃ antiferroelectric thick film at room temperature near room temperature. J. Mater. Chem. C, 2015,3:1694-1699. DOI URL
[43]	ROŽIČ B, MALIČ B, URŠIČ H , et al. Direct measurements of the electrocaloric effect in bulk PbMg_1/3Nb_2/3O₃ (PMN) ceramics. Ferroelectrics, 2011,421(1):103-107. DOI URL
[44]	HAN L Y, GUO S B, YAN S G , et al. Electrocaloric effect in Pb_0.3Ca_xSr_0.7-_xTiO₃ ceramics near room temperature. Journal of Inorganic Materials, 2019,34(9):1011-1014. DOI URL
[45]	PERÄNTIE J, TAILOR H N, HAGBERG J , et al. Electrocaloric properties in relaxor ferroelectric (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ system. J. Appl. Phys., 2013, 114(17): 174105-1-6.
[46]	GENG W P, LIU Y, MENG X J. Giant negative electrocaloric effect in antiferroelectric La-doped Pb(ZrTi)O₃ thin films near room temperature. Adv. Mater., 2015, 27(20): 3164-1-5.
[47]	BAI Y, ZHENG G P, DING K , et al. The giant electrocaloric effect and high effective cooling power near room temperature for BaTiO₃ thick film. J. Appl. Phys., 2011, 110(9): 094103-1-3.
[48]	JIANG X J, LUO L H, WANG B Y , et al. Electrocaloric effect based on the depolarization transition in (1-x)Bi_0.5Na_0.5TiO₃-xKNbO₃ lead-free ceramics. Ceram. Int., 2014,40(2):2627-2634. DOI URL
[49]	KUMAR S, SINGH S . Study of electrocaloric effect in lead-free 0.9K_0.5Na_0.5NbO₃-0.1CaZrO₃ solid solution ceramics. J. Mater. Sci.: Mater. Electron., 2019,30(14):12924-12928. DOI URL
[50]	NOVAK N, PIRC R, KUTNJAK Z . Effect of electric field on ferroelectric phase transition in BaTiO₃ ferroelectric. Ferroelectrics, 2014,469(1):61-66. DOI URL
[51]	QIAN X S, YE H J, ZHANG Y T , et al. Giant electrocaloric response over a broad temperature range in modified BaTiO₃ ceramics. Adv. Funct. Mater., 2014,24(9):1300-1305. DOI URL
[52]	BAI Y, HAN X, ZHENG X C , et al. Both high reliability and giant electrocaloric strength in BaTiO₃ ceramics. Sci. Rep., 2013, 3: 2895-1-5.
[53]	BAI Y, ZHENG G P, SHI S Q . Abnormal electrocaloric effect of Na_0.5Bi_0.5TiO₃-BaTiO₃ lead-free ferroelectric ceramics above room temperature. Mater. Res. Bull., 2011,46(11):1866-1869. DOI URL
[54]	PLAZNIK U, KITANOVSKI A, ROŽIČ B , et al. Bulk relaxor ferroelectric ceramics as a working body for an electrocaloric cooling device. Appl. Phys. Lett., 2015, 106(4): 043903-1-4.
[55]	CHUKKA R, VANDRANGI S, SHANNIGRAHI S , et al. An electrocaloric device demonstrator for solid-state cooling. EPL-Europhys. Lett., 2013, 103: 47011-1-4.
[56]	ZHANG T, QIAN X S, GU H M , et al. An electrocaloric refrigerator with direct solid to solid regeneration. Appl. Phys. Lett., 2017, 110(24): 243503-1-4.
[57]	BLUMENTHAL P, RAATZ A . Design methodology for electrocaloric cooling systems. Energy Technol., 2018,6(8):1560-1566. DOI URL
[58]	MOYA X, DEFAY E, MATHUR N D , et al. Electrocaloric effects in multilayer capacitors for cooling applications. MRS Bulletin, 2018,43(4):291-294. DOI URL
[59]	MA R J, ZHANG Z Y, TONG K , et al. Highly efficient electrocaloric cooling with electrostatic actuation. Science, 2017,357(6356):1130-1134. DOI URL
[60]	Li X Y . Electrocaloric Effect in Relaxor Ferroelectric Materials. Pennsylvania: The Pennsylvania State University Doctoral Dissertation, 2013.
[61]	ROŽIČ B, MALIČ B, URŠIČ H , et al. Direct measurements of the giant electrocaloric effect in soft and solid ferroelectric materials. Ferroelectrics, 2010,405(1):26-31. DOI URL
[62]	SANLIALP M, MOLIN C, SHVARTSMAN V V , et al. Modified differential scanning calorimeter for direct electrocaloric measurements. IEEE Trans. Ultrason. Ferroelectrics, 2016,63(10):1690-1696.
[63]	QI S, ZHANG G H, DUAN L H , et al. Electrocaloric effect in Pb-free Sr-doped BaTi_0.9Sn_0.1O₃ ceramics. Mater. Res. Bull., 2017,91:31-35. DOI URL
[64]	LI J T, BAI Y, QIN S Q , Direct and indirect characterization of electrocaloric effect in (Na, K)NbO₃ based lead-free ceramics. Appl. Phys. Lett., 2016, 109(16): 162902-1-4.
[65]	ZHOU Y Z, LIN Q R, LIU W F , et al. Compositional dependence of electrocaloric effect in lead-free (1-x)Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃ ceramics. RCS Adv., 2016,6(17):14084-14089.
[66]	ROSE M C, COHEN R E. Giant electrocaloric effect around T_C. Phys. Rev. Lett., 2012, 109(18): 187604-1-5.
[67]	ZHAO L, KE X Q, ZHOU Z J , et al. Large electrocaloric effect over a wide temperature range in BaTiO₃-modified lead-free ceramics. J. Mater. Chem. C, 2019,7:1353-1358. DOI URL
[68]	NIE X, YAN S G, CHEN X F, et al. Correlation between electrocaloric response and polarization behavior: slim-like and square-like hysteresis loop. Phys. Status Solidi A, 2018, 215(13): 1700971-1-7.
[69]	张良莹, 姚熹 . 电介质物理. 西安: 西安交通大学, 2008: 432-480.
[70]	王国梅, 万发荣 . 材料物理. 武汉:武汉理工大学出版社, 2004: 179-192.
[71]	殷之文 . 电介质物理学. 北京: 科学出版社, 2003: 473-483.
[72]	钟维烈 . 铁电体物理学. 北京: 科学出版社, 2018: 68-148.
[73]	KARAKI T, KATAYAMA T, YOSHIDA K , et al. Morphotropic phase boundary slope of (K, Na, Li)NbO₃-BaZrO₃ binary system adjusted using third component (Bi, Na)TiO₃ additive. Jpn. J. Appl. Phys., 2013, 52(9S1): 09KD11-1-4.
[74]	SASAKI A, CHIBA T, MAMIYA Y , et al. Dielectric and piezoelectric properties of (Bi_0.5Na_0.5)TiO₃-(Bi_0.5K_0.5)TiO₃ systems. Jpn. J. Appl. Phys., 1999,38(9):5564-5567. DOI URL
[75]	CHUKKA R, CHEAH J W, CHEN Z H , et al. Enhanced cooling capacities of ferroelectric materials at morphotropic phase boundaries. Appl. Phys. Lett., 2011, 98(24): 242902-1-3.
[76]	ZHANG T D, LI W L, CAO W P , et al. Giant electrocaloric effect in PZT bilayer thin films by utilizing the electric field engineering. Appl. Phys. Lett., 2016, 108(216): 162902-1-5.
[77]	YAO F Z, YU Q, WANG K , et al. Ferroelectric domain morphology and temperature-dependent piezoelectricity of (K, Na, Li)(Nb, Ta, Sb)O₃ lead-free piezoceramics. RSC Adv., 2014,4:20062-20068. DOI URL
[78]	GOTTSCHALL T, BENKE D, FRIES M , et al. A matter of size and stress: understanding the first-order transition in materials for solid-state refrigeration. Adv. Funct. Mater., 2017, 27(32): 1606735-1-6.
[79]	WANG D W, HUSSAIN F, KHESRO A , et al. Composition and temperature dependence of structure and piezoelectricity in (1-x)(K_1-_yNa_y)NbO₃-x(Bi_1/2Na_1/2)ZrO₃ lead-free ceramics. J. Am. Ceram. Soc., 2017,100:627-637. DOI URL
[80]	SRIKANTH K S, SINGH V P, VAISH R . Enhanced pyroelectric figure of merits of porous BaSn_0.05Ti_0.95O₃ ceramics. J. Eur. Ceram. Soc., 2017,37(13):3943-3950. DOI URL
[81]	KIM H K, SHI F G . Thickness dependent dielectric strength of a low-permittivity dielectric film. IEEE Trans. Electr. In., 2001,8(2):248-252.
[82]	CHEN G, ZHAO J W, LI S T , et al. Origin of thickness dependent dc electrical breakdown in dielectrics. Appl. Phys. Lett., 2012, 100(22): 222904-1-4.
[83]	LIU X Q, CHEN T T, FU M S , et al. Electrocaloric effects in spark plasma sintered Ba_0.7Sr_0.3TiO₃-based ceramics: effects of domain sizes and phase constitution. Ceram. Int., 2014,40(7):11269-11276. DOI URL
[84]	内野研二 . 铁电器件, 2版. 西安: 西安交通大学出版社, 2017: 15-17.
[85]	MARATHE M, GRÜNEBOHM A, NISHIMATSU T , et al. First-principles-based calculation of the electrocaloric effect in BaTiO₃: a comparison of direct and indirect methods. Phys. Rev. B, 2016, 93: 054110-1-10.
[86]	NOVAK N, PIRC R, KUTNJAK Z. Impact of critical point on piezoelectric and electrocaloric response in barium titanate. Phys. Rev. B, 2013, 87: 104102-1-5.
[87]	NISHIMATSU T, BARR J A, BECKMAN S P. Direct molecular dynamics simulation of electrocaloric effect BaTiO₃. J. Phys. Soc. Jpn., 2013, 82(11): 114605-1-5.
[88]	HAN F, BAI Y, QIAO L J , et al. A systematic modification of the large electrocaloric effect within a broad temperature range in rare-earth doped BaTiO₃ ceramics. J. Mater. Chem. C, 2016,4(9):1842-1849. DOI URL
[89]	BAI Y, HAN F, XIE S , et al. Thickness dependence of electrocaloric effect in high-temperature sintered Ba_0.8Sr_0.2TiO₃ ceramics. J. Alloys Compd., 2018,736:57-61. DOI URL
[90]	YU Z, ANG C, GUO R , et al. Piezoelectric and strain properties of Ba(Ti₁-_xZr_x)O₃ ceramics. J. Appl. Phys., 2002,92(3):1489-1493. DOI URL
[91]	YAO Y G, ZHOU C, LYU D C , et al. Large piezoelectricity and dielectric permittivity in BaTiO₃-xBaSnO₃ system: the role of phase coexisting. Europhysics Letters, 2012, 98(2): 27008-1-6.
[92]	WEYLAND F, EISELE T, STEINER S , et al. Long term stability of electrocaloric response in barium zirconate titanate. J. Eur. Ceram. Soc., 2017,38(2):551-556. DOI URL
[93]	ZHANG X, WU L, GAO S , et al. Large electrocaloric effect in Ba(Ti_1-_xSn_x)O₃ ceramics over a broad temperature region. AIP Adv., 2015, 5: 047134-1-7.
[94]	SANLIALP M, LUO Z D, SHVARTSMAN V V , et al. Direct measurement of electrocaloric effect in lead-free Ba(Sn_xTi_1-_x)O₃ ceramics. Appl. Phys. Lett., 2017, 111(17): 173903-1-5.
[95]	HIROSHI M. Temperature dependences of the electromechanical and electrocaloric properties of Ba(Zr, Ti)O₃ and (Ba, Sr)TiO₃ ceramics. Jpn. J. Appl. Phys., 2017, 56: 10PC05-1-8.
[96]	JIAN X D, LU B, LI D D , et al. Direct measurement of large electrocaloric effect in Ba(Zr_xTi₁-_x)O₃ ceramics. ACS Appl. Mater. Interfaces, 2018,10(5):4801-4807. DOI URL
[97]	LUO Z D, ZHANG D W, YANG L , et al. Enhanced electrocaloric effect in lead-free BaTi₁-_xSn_xO₃ ceramics near room temperature. Appl. Phys. Lett., 2014, 105(10): 102904-1-5.
[98]	LIU W F, REN X B. Large piezoelectric effect in Pb-free ceramics. Phys. Rev. Lett., 2009, 103(25): 257602-1-4.
[99]	XU Z P, QIANG H, CHEN Y , et al. Room-temperature electrocaloric effect in (1-x)Ba_0.67Sr_0.33TiO₃-xBa_0.9Ca_0.1Ti_0.9Zr_0.1O₃ ceramics under moderate electric field. J. Mater. Sci.: Mater. Electron., 2018,29(9):7227-7232. DOI URL
[100]	TSAI C C, CHAO W H, CHU S Y, et al. Enhanced temperature stability and quality factor with Hf substitution for Sn and MnO₂ doping of (Ba_0.97Ca_0.03)(Ti_0.96Sn_0.04)O₃ lead-free piezoelectric ceramics with high Curie temperature. AIP Advances, 2016, 6(12): 125024-1-16.
[101]	NIE X, YAN S, GUO S , et al. The influence of phase transition on electrocaloric effect in lead-free (Ba_0.9Ca_0.1)(Ti₁-_xZr_x)O₃ ceramics. J. Am. Ceram. Soc., 2017,100(11):5202-5210. DOI URL
[102]	PATEL S, VAISH R . Effect of sintering temperature and dwell time on electrocaloric properties of Ba_0.85Ca_0.075Sr_0.075Ti_0.90Zr_0.10O₃ ceramics. Phase Transit., 2017,90(5):465-474. DOI URL
[103]	HAO J G, XU Z J, CHU R Q , et al. Fatigue-resistant, temperature- insensitive strain behavior and strong red photoluminescence in Pr-modified 0.92(Bi_0.5Na_0.5)TiO₃-0.08(Ba_0.90Ca_0.10)(Ti_0.92Sn_0.08)O₃ lead-free ceramics. J. Eur. Ceram. Soc., 2017,37(2):877-882. DOI URL
[104]	FAN Z M, LIU X M, TAN X L . Large electrocaloric responses in [Bi_1/2(Na, K)_1/2]TiO₃-based ceramics with giant electrostrains. J. Am. Ceram. Soc., 2017,100(5):2088-2097. DOI URL
[105]	RIEMER L M, LALITHA K V, JIANG X J , et al. Stress-induced phase transition in lead-free relaxor ferroelectric composites. Acta Mater., 2017,136:271-280. DOI URL
[106]	CHAUHAN A, PATEL S, VAISH R . Enhanced electrocaloric effect in pre-stressed ferroelectric materials. Energy Technol., 2015,3(2):177-186. DOI URL
[107]	CAO W P, LI W L, XU D , et al. Enhanced electrocaloric effect in lead-free NBT-based ceramics. Ceram. Int., 2014,40(7):9273-9278. DOI URL
[108]	CAO W P, LI W L, DAI X F , et al. Large electrocaloric response and high energy-storage properties over a broad temperature range in lead-free NBT-ST ceramics. J. Eur. Ceram. Soc., 2016,36(3):593-600. DOI URL
[109]	PONOMAREVA I, LISENKOV S. Bridging the macroscopic and atomistic descriptions of the electrocaloric effect. Phys. Rev. Lett., 2012, 108(16): 167604-1-5.
[110]	ZANNEN M, LAHMAR A, KUTNJAK Z , et al. Electrocaloric effect and energy storage in lead free Gd_0.02Na_0.5Bi_0.48TiO₃ ceramic. Solid State Sci., 2017,66:31-37. DOI URL
[111]	LUO L H, JIANG X J, ZHANG Y Y , et al. Electrocaloric effect and pyroelectric energy harvesting of (0.94-x)Na_0.5Bi_0.5TiO₃- 0.06BaTiO₃-xSrTiO₃ ceramics. J. Eur. Ceram. Soc., 2017,37(8):2803-2812. DOI URL
[112]	LE GOUPIL F, BENNETT J, AXELSSON A K , et al. Electrocaloric enhancement near the morphotropic phase boundary in lead-free NBT-KBT ceramics. Appl. Phys. Lett., 2015, 107(17): 172903-1-4.
[113]	LE GOUPIL F, ALFORD N M. Upper limit of the electrocaloric peak in lead-free ferroelectric relaxor ceramics. APL Mater., 2016, 4(6): 064104-1-6.
[114]	LE GOUPIL F, MCKINNON R, KOVAL V , et al. Tuning the electrocaloric enhancement near the morphotropic phase boundary in lead-free ceramics. Sci. Rep., 2016, 6: 28251-1-6.
[115]	WEYLAND F, ACOSTA M, KORUZA J , et al. Criticality: concept to enhance the piezoelectric and electrocaloric properties of ferroelectrics. Adv. Funct. Mater., 2016,26(40):7326-7333. DOI URL
[116]	LI F, CHEN G R, LIU X , et al. Phase-composition and temperature dependence of electrocaloric effect in lead-free Bi_0.5Na_0.5TiO₃- BaTiO₃-(Sr_0.7Bi_0.2□_0.1)TiO₃ ceramics. J. Eur. Ceram. Soc., 2017,37(15):4732-4740. DOI URL
[117]	LI J L, ZHAO X B, XU Z , et al. Electrocaloric effect in lead-free relaxor (1-x)(Sr_0.7Bi_0.2)TiO₃+x(Na_0.5Bi_0.5)TiO₃ material system. Mater. Lett., 2017,187:68-71. DOI URL
[118]	LI Q, WANG J, MA L T , et al. Large electrocaloric effect in (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ lead-free ferroelectric ceramics by La₂O₃ addition. Mater. Res. Bull., 2016,74:57-61. DOI URL
[119]	TUNKASIRI T, RUJIJANAGUL G . Dielectric strength of fine grained barium titanate ceramics. J. Mater. Sci. Lett., 1996,15(20):1767-1769. DOI URL
[120]	DU H L, YANG Z T, GAO F , et al. Lead-free nonlinear dielectric ceramics for energy storage application: current status and challenges. Journal of Inorganic Materials, 2018,33(10):1046-1058. DOI URL
[121]	ROŽIČ B, KORUZA J, KUTNJAK Z , et al. The electrocaloric effect in lead-free K_0.5Na_0.5NbO₃-SrTiO₃ ceramics. Ferroelectrics, 2013,446(1):39-45. DOI URL
[122]	KORUZA J, ROŽIČ B, CORDOYIANNIS G , et al. Large electrocaloric effect in lead-free K_0.5Na_0.5NbO₃-SrTiO₃ ceramics. Appl. Phys. Lett., 2015, 106(20): 202905-1-4.
[123]	GUPTA A, KUMAR R, SINGH S . Coexistence of negative and positive electrocaloric effect in lead-free 0.9(K_0.5Na_0.5)NbO₃-0.1SrTiO₃ nanocrystalline ceramics. Scripta Mater., 2018,143:5-9. DOI URL
[124]	KUMAR R, SINGH S . Enhanced electrocaloric effect in lead-free 0.9(K_0.5Na_0.5)NbO₃-0.1Sr(Sc_0.5Nb_0.5)O₃ ferroelectric nanocrystalline ceramics. Alloys Compd., 2017,723:589-594. DOI URL
[125]	WANG X J, WU J G, DKHIL B , et al. Enhanced electrocaloric effect near polymorphic phase boundary in lead-free potassium sodium niobate ceramics. Appl. Phys. Lett., 2017, 110(6): 063904-1-5.
[126]	KUMAR R, SINGH S . Giant electrocaloric and energy storage performance of [(K_0.5Na_0.5)NbO₃](1-x)-(LiSbO₃)x nanocrystalline ceramics. Sci. Rep., 2018, 8(1): : 3186-1-9.
[127]	LI F, LU B, ZHAI J W , et al. Enhanced piezoelectric properties and electrocaloric effect in novel lead-free (Bi_0.5K_0.5)TiO₃-La(Mg_0.5Ti_0.5)O₃ ceramics. J. Am. Ceram. Soc., 2018,101(12):5503-5513. DOI URL
[128]	TAO H, YANG J L, LYU X , et al. Electrocaloric behavior and piezoelectric effect in relaxor NaNbO₃-based ceramics. J. Am. Ceram. Soc., 2019,102(5):2578-2586.
[129]	YU Y, GAO F, WEYLAND F , et al. Significantly enhanced room temperature electrocaloric response with superior thermal stability in sodium niobate-based bulk ceramics. J. Mater. Chem. A, 2019,7(19):11665-11672. DOI URL
[130]	AXELSSON A K, LE GOUPIL F, VALANT M , et al. Electrocaloric effect in lead-free Aurivillius relaxor ferroelectric ceramics. Acta Mater., 2017,124:120-126. DOI URL