Exploring the Pb1-x Srx HfO3 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-film heterostructures on SrTiO3 (001) substrates with the added opportunity of observing a morphotropic phase boundary in the Pb1-x Srx HfO3 system akin to that in PbZrx Ti1-x O3 . The resulting (240)-oriented PbHfO3 (Pba2) films were found to exhibit antiferroelectric switching with a saturation polarization ⁓53 μC/cm2 at 1.6 MV/cm and a weak-field dielectric constant ≈186 at 298 K. Temperature-dependent dielectric measurements revealed an antiferroelectric-to-paraelectric phase transition at ∼518 K. Further, (002)-oriented SrHfO3 films were synthesized, but were found to not exhibit ferroelectric behavior; nor did we observe evidence of a recently reported polar P4mm phase. Instead, the SrHfO3 films were found to exhibit 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 MV/cm to 3 MV/cm). While the lack of ferroelectric order in SrHfO3 removed the potential for a PbZrx Ti1-x O3 -like morphotropic phase boundary, we proceeded to explore the structural and property evolution of the Pb1-x Srx HfO3 (0 ≤ x <\xa01) system. Strontium alloying was found to increase the electric-breakdown strength (EB ) and decrease the hysteresis loss resulting in concurrent enhancement of the capacitive energy storage density (Ur ) and efficiency (η). An optimum composition (Pb0.5 Sr0.5 HfO3 ) was found to produce the best combination of EB = 5.12\xa0± 0.5 MV/cm, Ur = 77\xa0± 5 J/cm3 , and η = 97\xa0± 2%; well out-performing PbHfO3 and other antiferroelectric oxides. This article is protected by copyright. All rights reserved.