The discovery of ferroelectricity in both pure and doped HfO 2 -based thin films have revitalized the interest in using ferroelectrics for nanoscale device applications. To take advantage of this silicon-compatible ferroelectric, fundamental questions such as the origin of ferroelectricity and better approach to controlled realization of ferroelectricity at the nanoscale need to be addressed. The emergence of robust polarization in HfO 2based thin films is considered as the cumulative effect of various extrinsic factors such as finite-size effects and surface/interface effects of small grains, compressive stress, dopants, oxygen vacancies, and electric fields. The kinetic effects of phase transitions P bca, become thermodynamically stable in (111)-oriented thin films over a wide range of epitaxial strain conditions. This work suggests a potential avenue to better stabilize the ferroelectric phase in HfO 2 thin films through substrate orientation engineering.

Harvesting waste heat for useful purposes is an essential component of improving the efficiency of primary energy utilization. Today, approaches such as pyroelectric energy conversion are receiving renewed interest for their ability to turn wasted energy back into useful energy. From this perspective, the need for these approaches, the basic mechanisms and processes underlying their operation, and the material and device requirements behind pyroelectric energy conversion are reviewed, and the potential for advances in this area is also discussed.

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Currently, there is a lack of nonvolatile memory (NVM) technology that can operate continuously at temperatures >200 °C. While ferroelectric NVM has previously demonstrated long polarization retention and >1013 read/write cycles at room temperature, the largest hurdle comes at higher temperatures for conventional perovskite ferroelectrics. Here, we demonstrate how AlScN can enable high-temperature (>200 °C) nonvolatile memory. The c-axis textured thin films were prepared via reactive radiofrequency magnetron sputtering onto a highly textured Pt (111) surface. Photolithographically defined Pt top electrodes completed the capacitor stack, which was tested in a high temperature vacuum probe station up to 400 °C. Polarization–electric field hysteresis loops between 23 and 400 °C reveal minimal changes in the remanent polarization values, while the coercive field decreased from 4.3 MV/cm to 2.6 MV/cm. Even at 400 °C, the polarization retention exhibited negligible loss for up to 1000 s, demonstrating promise for potential nonvolatile memory capable of high−temperature operation. Fatigue behavior also showed a moderate dependence on operating temperature, but the mechanisms of degradation require additional study.

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−xSrxHfO3 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−xSrxHfO3 (0 ≤ x < 1) system is explored. Strontium alloying increased the electric‐breakdown strength (EB) and decreased hysteresis loss, thus enhancing the capacitive energy storage density (Ur) and efficiency (η). The composition, Pb0.5Sr0.5HfO3 produced the best combination of EB = 5.12 ± 0.5 MV cm−1, Ur = 77 ± 5 J cm−3, and η = 97 ± 2%, well out‐performing PbHfO3 and other antiferroelectric oxides.