Enhanced energy storage properties and antiferroelectric stability of Mn-doped NaNbO3-CaHfO3lead-free ceramics: Regulating phase structure and tolerance factor

NaNbO3-based ceramics usually show ferroelectric-like P-Eloops at room temperature due to the irreversible transformation of the antiferroelectric orthorhombic phase to ferroelectric orthorhombic phase, which is not conducive to energy storage applications. Our previous work found that incorporating CaHfO3into NaNbO3can stabilize its antiferroelectric phase by reducing the tolerance factor (t), as indicated by the appearance of characteristic double P-Eloops. Furthermore, a small amount of MnO2addition effectively regulate the phase structure and tolerance factor of 0.94NaNbO3-0.06CaHfO3(0.94NN-0.06CH), which can further improve the stability of antiferroelectricity. The XRD and XPS results reveal that the Mn ions preferentially replace A-sites and then B-sites as increasing MnO2. The antiferroelectric orthorhombic phase first increases and then decreases, while the tshows the reversed trend, thus an enhanced antiferroelectricity and the energy storage density Wrecof 1.69 J/cm3at 240 kV/cm are obtained for 0.94NN-0.06CH-0.5%MnO2(in mass fraction). With the increase of Mn content to 1.0 % from 0.5 %, the efficiency increases to 81 % from 45 %, although the energy storage density decreases to 1.31 J/cm3due to both increased tolerance factor and non-polar phase.