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1. Polarization switching in Hf _0.5 Zr _0.5 O ₂ -dielectric stack: The role of dielectric layer thickness

   https://doi.org/10.1063/5.0056448  

   Saha, Atanu K.; Si, Mengwei; Ye, Peide D.; Gupta, Sumeet K. (September 2021, Applied Physics Letters)
2. Optical dielectric properties of HfO ₂ -based films

   https://doi.org/10.1116/6.0001651  

   Dou, Hongyi; Strkalj, Nives; Zhang, Yizhi; MacManus-Driscoll, Judith L.; Jia, Quanxi; Wang, Haiyan (May 2022, Journal of Vacuum Science & Technology A)

   We report the dielectric Properties of HfO 2 -based films in the optical–high frequency range. The demonstrated tunability of the optical dielectric constant of HfO 2 -based compounds is of great relevance for optoelectronic applications, e.g., high-refractive index dielectrics for nanoantenna and optical coatings for electronic displays. Since the optical dielectric constant of HfO 2 is determined by the electronic structure and its crystal environment, we tune the physical properties of HfO 2 films on MgO by adding different dopants. In this work, we aim to determine the influence of doping together with the resulting crystal structure on the optical dielectric constant. Hence, we studied 20 mol. % Y-doped HfO 2 (HYO), Hf 0.5 Zr 0.5 O 2 (HZO), and Hf 0.5 Ce 0.5 O 2 (HCO). Among the dopants, Y 2 O 3 has the lowest, ZrO 2 an intermediate, and CeO 2 the highest real part of the optical dielectric constant. The optical dielectric constant is found to be lowest in the cubic HYO films. An intermediate dielectric constant is found in HZO films that is predominantly in the monoclinic phase, but additionally hosts the cubic phase. The highest dielectric constant is observed in HCO films that are predominantly in the cubic phase with inclusions of the monoclinic phase. The observed trend is in good agreement with the dominant role of the dopant type in setting the optical dielectric constant. 

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3. Temperature dependence of dielectric nonlinearity of BaTiO ₃ ceramics

   https://doi.org/10.20517/microstructures.2023.43  

   Fujii, Ichiro; Trolier-McKinstry, Susan (November 2023, Microstructures)

   In many commercially utilized ferroelectric materials, the motion of domain walls is an important contributor to the functional dielectric and piezoelectric responses. This paper compares the temperature dependence of domain wall motion for BaTiO3 ceramics with different grain sizes, point defect concentrations, and formulations. The grain boundaries act as significant pinning points for domain wall motion such that fine-grained materials show smaller extrinsic contributions to the properties below the Curie temperature and lower residual ferroelectric contributions immediately above the Curie temperature. Oxygen vacancy point defects make a modest change in the extrinsic contributions of undoped BaTiO3 ceramics. In formulated BaTiO3, extrinsic contributions to the dielectric response were suppressed over a wide temperature range. It is believed this is due to a combination of reduced grain size, the existence of a core-shell microstructure, and a reduction in domain wall continuity over the grain boundaries. 

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4. Dielectric Function of VO ₂ determined by Spectroscopic Ellipsometry

   https://doi.org/10.1109/RAPID54473.2023.10264735  

   Louisos, Dustin; McLamb, Micheal; Ginn, James; Warren, Andrew P.; Boreman, Glenn D.; Mencagli, Mario Junior; Willis, Andrew; Hofmann, Tino; Touma, Jimmy E. (September 2023, IEEE)
5. Mid‐ to Far‐Infrared Anisotropic Dielectric Function of HfS ₂ and HfSe ₂

   https://doi.org/10.1002/adom.202200933  

   Kowalski, Ryan_A; Nolen, Joshua_Ryan; Varnavides, Georgios; Silva, Sebastian_Mika; Allen, Jack_E; Ciccarino, Christopher_J; Juraschek, Dominik_M; Law, Stephanie; Narang, Prineha; Caldwell, Joshua_D (September 2022, Advanced Optical Materials)

   Abstract The far‐infrared (far‐IR) remains a relatively underexplored region of the electromagnetic spectrum extending roughly from 20 to 100 µm in free‐space wavelength. Research within this range has been restricted due to a lack of optical materials that can be optimized to reduce losses and increase sensitivity, as well as by the long free‐space wavelengths associated with this spectral region. Here the exceptionally broad Reststrahlen bands of two Hf‐based transition metal dichalcogenides (TMDs) that can support surface phonon polaritons (SPhPs) within the mid‐infrared (mid‐IR) into the terahertz (THz) are reported. In this vein, the IR transmission and reflectance spectra of hafnium disulfide (HfS₂) and hafnium diselenide (HfSe₂) flakes are measured and their corresponding dielectric functions are extracted. These exceptionally broad Reststrahlen bands (HfS₂: 165 cm⁻¹; HfSe₂: 95 cm⁻¹) dramatically exceed that of the more commonly explored molybdenum‐ (Mo) and tungsten‐ (W) based TMDs (≈5–10 cm⁻¹), which results from the over sevenfold increase in the Born effective charge of the Hf‐containing compounds. This work therefore identifies a class of materials for nanophotonic and sensing applications in the mid‐ to far‐IR, such as deeply sub‐diffractional hyperbolic and polaritonic optical antennas, as is predicted via electromagnetic simulations using the extracted dielectric function. 

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