## 3 Results and Discussion  
The total polarization (sum of the FE phase and AFE phase) as a function of temperature was calculated for different Sm compositions, shown in Figure 2a. It can be seen that the polarization of pure BFO indicates a first-order phase transition at 1100 K. As the composition of Sm in the BFO system increases, AFE phases are gradually observed. Meanwhile, the transition temperature decreases significantly with increasing Sm composition. As the Sm composition increases above 0.15 Sm-BFO, all the FE phase transforms to AFE phase. Similarly, hydrostatic pressure also can induce the AFE phase and decrease the transition temperature, as shown in Figure 2b. The temperature range of the FE phase decreases with hydrostatic pressure, and the FE phase disappears at a hydrostatic pressure higher than 5 GPa. Figure 2: The total polarization with (**a**) Sm compositions and (**b**) hydrostatic pressures as a function of temperature. First, the temperature span of the EC effect at different Sm compositions was studied. The entropy changes of the EC effect in 0.05 Sm-BFO and 0.10 Sm-BFO were investigated, as shown in Figure 3. Figure 3a shows the entropy change as a function of temperature with different electric fields including 10, 20, 30 and 40 kV/cm. At 10 kV/cm, the entropy change has two peaks at 834 K and 853 K, which results from FE to AFE, and AFE to PE phase transitions, respectively. In addition, the entropy change also increases with the electric field. The large entropy changes \(\Delta S\) of \(\sim\)5 J/(kg-K) and \(\sim\)4 J/(kg-K) were obtained in 0.05 Sm-BFO and 0.10 Sm-BFO at an electric field of 40 kV/cm. Remarkably, compared to previous works, we observed a large EC strength (\(|\Delta S|/|\Delta E|\)) in Sm-BFO. For example, BaTiO\({}_{3}\) thick films exhibited a giant EC effect of \(\Delta S=\) 10.1 J/(kg-K) at 800 kV/cm [42]. Therefore, the maximum EC strength in Sm-BFO can be obtained at 0.29 J-cm/(kg-K-kV), which is one order of magnitude larger than BaTiO\({}_{3}\) thick films (0.013 J-cm/(kg-K-kV)). Furthermore, the temperature range of the entropy change in 0.10 Sm-BFO (\(\sim\)31 K) is wider than that in 0.05 Sm-BFO (\(\sim\)18 K), indicating that Sm-doping can broaden the temperature range of the EC effect. In addition, the entropy changes of BFO as a function of temperature, at 0 GPa and 3 GPa, are shown in Figure 4. As shown in Figure 4a, the value of the entropy change increases with the increasing of the electric field, while only one peak of entropy change can be observed because only FEPE phase transition occurs. However, at 3 GPa hydrostatic pressure on pure BFO, there are two peaks of entropy change (Figure 4b). Since hydrostatic pressure can cause the appearance of the AFE phase, the FEAFEPE phase transition can broaden the temperature range of the EC effect. The AFE phase can be increased by increasing the hydrostatic pressure, and the temperature range (\(\sim\)64 K) becomes wider than that (\(\sim\)44 K) observed at 0 GPa hydrostatic pressure. Figure 4: Entropy changes of BFO with different electric fields as a function of temperature under (**a**) 0 GPa and (**b**) 3 GPa. Figure 3: Entropy changes of (**a**) 0.05 Sm-BFO (BiFeO\({}_{3}\)) and (**b**) 0.10 Sm-BFO as a function of temperature under different electric fields of 10, 20, 30, and 40 kV/cm. According to the above results, the Sm doping composition and hydrostatic pressure have a strong influence on the EC effect on temperature range and transition temperature. Therefore, we continued investigate the Sm doping composition and hydrostatic pressure to gain a broad temperature range under an ultralow electric field in Figure 5. As shown in Figure 5a, there are two peaks of entropy change, and the value of the entropy change increases with an increasing of the electric field. The transition temperature range of 0.05 Sm-BFO can be broadened by applying 3 GPa of hydrostatic pressure.