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Epitaxial PbHf1−xTixO3/SrTiO3(001) thin-film heterostructures are studied for a potential morphotropic phase boundary (MPB) akin to that in the PbZr1−xTixO3 system. End members, PbHfO3 and PbTiO3, were found to possess orthorhombic (Pbam) and tetragonal (P4mm) crystal structures and antiferroelectric and ferroelectric (∼87 μC/cm2) behavior, respectively. PbHf0.75Ti0.25O3 and PbHf0.25Ti0.75O3 solid solutions were both found to be ferroelectric with rhombohedral (R3c, ∼22 μC/cm2) and tetragonal (P4mm, ∼46 μC/ cm2) structures, respectively. For intermediate PbHf1−xTixO3 compositions (e.g., x = 0.4, 0.45, 0.5, and 0.55), a structural transition was observed from rhombohedral (hafnium-rich) to tetragonal (titanium-rich) phases. These intermediate compositions also exhibited mixed-phase structures including R3c, monoclinic (Cm), and P4mm symmetries and, in all cases, were ferroelectric with remanent (5−22 μC/cm2) and saturation (18.5−36 μC/cm2) polarization and coercive field (24−34.5 kV/cm) values increasing with x. While the dielectric constant was the largest for PbHf0.6Ti0.4O3, the MPB is thought to be near x = 0.5 after separation of the intrinsic and extrinsic contributions to the dielectric response. Furthermore, piezoelectric displacement−voltage hysteresis loops were obtained for all chemistries revealing displacement values as good as PbZr0.52Ti0.48O3 films in the same geometry. Thereby, the PbHf1−xTixO3 system is a viable alternative to the PbZr1−xTixO3 system offering comparable performance.

Ab initio methods provide a powerful tool in the search for novel polar materials. In particular, there has been a surge to identify lead-free piezoelectric materials to replace PbZr0.52Ti0.48O3. This study examines a computational strategy to identify increased piezoelectric and dielectric responses of alloy systems based on the linear interpolation of force constants, Born effective charges, and internal strain tensors from their end-point compounds. We choose the ferroelectric layered perovskite Sr2Nb2O7as a parent structure and employ this alloying strategy for 19 potential cation substitutions, targeting thermodynamically metastable alloys with high piezoelectric response. From this screening, we identify Sr2Nb2-2xV2xO7as a promising polar system. We conduct large-unit-cell calculations of Sr2Nb2-2xV2xO7at x = 0.0625, 0.125 for multiple cation orderings and find a significant 184% enhanced piezoelectric response. The solid solution system is synthesized as single-crystalline thin-film heterostructures using pulsed-laser deposition, and an enhanced dielectric response is observed at x = 0.05 and at x = 0.1. We present the Sr2Nb2-2xV2xO7alloy system designed through high-throughput computational screening methods with a large calculated piezoelectric response and experimentally verified increased dielectric response. Our methodology is provided as a high-throughput screening tool for novel materials with enhanced polarizability and alloy systems with potential morphotropic phase boundaries.

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 Pb1- x Srx HfO3 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 Pb1- x Srx HfO3 (0 ≤ x

Current high-performing piezoelectric materials are dominated by perovskites that rely on soft optical phonon modes stabilized by disorder near a morphotropic phase boundary and a unique resilience of the polar response to that disorder. To identify structural families with similar resilience, we develop a first-principles sensitivity analysis approach to determine the effect of disorder on the piezoelectric response for structures in the Materials Project database. In well-known piezoelectric systems, the lattice dynamics, rather than internal strain or dielectric, control the polar response. Additionally, multiple stable optical phonon modes are found to contribute to the piezoelectric response, providing a fingerprint for disorder tolerance. A multiple-phonon mode criterion is used to evaluate candidate materials for disorder-tolerant piezoelectric prototype systems. Five promising structures are altered through chemical substitution, generating potential MPB end points with large piezoelectric responses beyond perovskites including Akermanite Sr2xCa2 - 2xCoSi2O7, which exhibits a nearly 20% increase in response at the 50% composition.

Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for obtaining precise information about the local bonding of materials, but difficult to interpret without a well-vetted dataset of reference spectra. The ability to predict NMR parameters and connect them to three-dimensional local environments is critical for understanding more complex, long-range interactions. New computational methods have revealed structural information available from 29Si solid-state NMR by generating computed reference spectra for solids. Such predictions are useful for the identification of new silicon-containing compounds, and serve as a starting point for determination of the local environments present in amorphous structures. In this study, we have used 42 silicon sites as a benchmarking set to compare experimentally reported 29Si solid-state NMR spectra with those computed by CASTEP-NMR and Vienna Ab Initio Simulation Program (VASP). Data-driven approaches enable us to identify the source of discrepancies across a range of experimental and computational results. The information from NMR (in the form of an NMR tensor) has been validated, and in some cases corrected, in an effort to catalog these for the local spectroscopy database infrastructure (LSDI), where over 10,000 29Si NMR tensors for crystalline materials have been computed. Knowledge of specific tensor values can serve as the basis for executing NMR experiments with precision, optimizing conditions to capture the elements accurately. The ability to predict and compare experimental observables from a wide range of structures can aid researchers in their chemical assignments and structure determination, since the computed values enables the extension beyond tables of typical chemical shift (or shielding) ranges.

The hafnate perovskites PbHfO 3 (antiferroelectric) and SrHfO 3 ("potential" ferroelectric) are studied as epitaxial thin films on SrTiO 3 (001) substrates with the added opportunity of observing a morphotropic phase boundary (MPB) in the Pb 1- x Sr x HfO 3 system. The resulting (240)-oriented PbHfO 3 (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 SrHfO 3 films exhibited neither ferroelectric behavior nor evidence of a polar P4mm phase . Instead, the SrHfO 3 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 SrHfO 3 removes the potential for MPB, structural and property evolution of the Pb 1- x Sr x HfO 3 (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 0.5 Sr 0.5 HfO 3 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 PbHfO 3 and other antiferroelectric oxides., (© 2021 Wiley-VCH GmbH.)