Exploring the Pb_1−xSr_xHfO₃ System and Potential for High Capacitive Energy Storage Density and Efficiency

Abstract The hafnate perovskites PbHfO₃ (antiferroelectric) and SrHfO₃ (“potential” ferroelectric) are studied as epitaxial thin films on SrTiO₃ (001) substrates with the added opportunity of observing a morphotropic phase boundary (MPB) in the Pb_1−xSr_xHfO₃ system. The resulting (240)‐oriented PbHfO₃ (Pba2) films exhibited antiferroelectric switching with a saturation polarization ≈53 µC cm⁻² at 1.6 MV cm⁻¹, weak‐field dielectric constant ≈186 at 298 K, and an antiferroelectric‐to‐paraelectric phase transition at ≈518 K. (002)‐oriented SrHfO₃ films exhibited neither ferroelectric behavior nor evidence of a polar P4mm phase . Instead, the SrHfO₃ films exhibited a weak‐field dielectric constant ≈25 at 298 K and no signs of a structural transition to a polar phase as a function of temperature (77–623 K) and electric field (–3 to 3 MV cm⁻¹). While the lack of ferroelectric order in SrHfO₃ removes the potential for MPB, structural and property evolution of the Pb_1−xSr_xHfO₃ (0 ≤ x < 1) system is explored. Strontium alloying increased the electric‐breakdown strength (E_B) and decreased hysteresis loss, thus enhancing the capacitive energy storage density (U_r) and efficiency (η). The composition, Pb_0.5Sr_0.5HfO₃ produced the best combination of E_B = 5.12 ± 0.5 MV cm⁻¹, U_r = 77 ± 5 J cm⁻³, and η = 97 ± 2%, well out‐performing PbHfO₃ and other antiferroelectric oxides.