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1300www.MaterialsViews.com wileyonlinelibrary.com . IntroductionElectrocaloric effect (ECE), an electric fi eld induced temperature and/or entropy change of an insulating material, has attracted a great deal of attention after the recent fi ndings of large ECE in ceramic thin fi lms, polymers, and a dielectric fl uid. [1][2][3][4][5][6][7][8][9][10] Several recent works have also demonstrated potential of realizing high performance cooling devices exploiting large ECE in new electrocaloric (EC) materials. [11][12][13][14] In these newly developed EC materials, the giant ECE, i.e., large adiabatic temperature change Δ T and isothermal entropy change Δ S, were obtained under high applied electrical fi elds. For example, a | Δ T| = 35 K and Δ S = 160 Jkg −1 K −1 were induced in a high energy electron irradiated P(VDFTrFE) relaxor polymer under an electric fi eld change Δ E of 180 MVm −1 . [ 15 ] Analogously, in ferroelectric BaTiO 3 (BT) thick fi lms, a | Δ T| = 7.1 K and Δ S = 10.1 Jkg −1 K −1 were generated under the application of high electric fi elds change Δ E = 80 MVm −1 . [ 16 ] As one starts to address these EC materials for practical cooling devices applications, additional parameters should be considered besides a large Δ T and Δ S to measure the performance of EC materials. For instance, in order for cooling devices to be operated at low voltage such as <200 volts which is the normal voltage range for most cooling devices, an EC material with a large ECE induced under small electric fi elds is also important. In addition, a wide operational temperature range near room temperature is highly desired in order to develop high performance and practical EC cooling devices. [11][12][13][14] Therefore, one critical question is how to design and develop dielectric materials which are capable of generating giant ECE over a broad operation temperature with relatively low applied electric fi eld change Δ E.As a lead-free ferroelectric material which is environmentally friendly and is in fact the most widely used ferroelectric material, ECE in BT has been studied quite extensively in the past several years by many groups and in various forms including thin fi lms, bulk ceramics (including thick fi lms multilayer ceramic capacitors (MLCC)), and single crystals. [16][17][18][19][20][21][22] Large Δ T and Δ S have been reported in BT ceramics at temperatures near the ferroelectric-paraelectric (FE-PE) transition. [ 16 ] It is noted that for BT, besides the high temperature FE-PE transition (the transition temperature T FE-PE > 100 ° C) between the tetragonal ferroelectric (Tet) and cubic paraelectric phase, also exhibits an orthorhombic (O) and a rhombohedral (Rhom) phases as illustrated in Figure 1 (a). [ 23 ] As ECE is directly related to the entropy change of an insulation dielectric under the change of the applied electric fi eld, a dielectric with a polar phase which contains a large number of polar-states with similar energy levels can be induced under a reasonable electric fi eld from a nonpolar phase (i.e., belo...