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1. Colossal Strain Tuning of Ferroelectric Transitions in KNbO ₃ Thin Films

   https://doi.org/10.1002/adma.202408664  

   Hazra, Sankalpa; Schwaigert, Tobias; Ross, Aiden; Lu, Haidong; Saha, Utkarsh; Trinquet, Victor; Akkopru‐Akgun, Betul; Gregory, Benjamin Z; Mangu, Anudeep; Sarker, Suchismita; et al (December 2024, Advanced Materials)

   Abstract Strong coupling between polarization (P) and strain (ɛ) in ferroelectric complex oxides offers unique opportunities to dramatically tune their properties. Here colossal strain tuning of ferroelectricity in epitaxial KNbO₃thin films grown by sub‐oxide molecular beam epitaxy is demonstrated. While bulk KNbO₃exhibits three ferroelectric transitions and a Curie temperature (T_c) of ≈676 K, phase‐field modeling predicts that a biaxial strain of as little as −0.6% pushes itsT_c> 975 K, its decomposition temperature in air, and for −1.4% strain, toT_c> 1325 K, its melting point. Furthermore, a strain of −1.5% can stabilize a single phase throughout the entire temperature range of its stability. A combination of temperature‐dependent second harmonic generation measurements, synchrotron‐based X‐ray reciprocal space mapping, ferroelectric measurements, and transmission electron microscopy reveal a single tetragonal phase from 10 K to 975 K, an enhancement of ≈46% in the tetragonal phase remanent polarization (P_r), and a ≈200% enhancement in its optical second harmonic generation coefficients over bulk values. These properties in a lead‐free system, but with properties comparable or superior to lead‐based systems, make it an attractive candidate for applications ranging from high‐temperature ferroelectric memory to cryogenic temperature quantum computing. 

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2. A Landau–Devonshire analysis of strain effects on ferroelectric Al _1−x Sc _x N

   https://doi.org/10.1063/5.0098979  

   Yazawa, Keisuke; Zakutayev, Andriy; Brennecka, Geoff L. (July 2022, Applied Physics Letters)

   We present a thermodynamic analysis of the recently discovered nitride ferroelectric materials using the classic Landau–Devonshire approach. Electrostrictive and dielectric stiffness coefficients of Al 1− x Sc x N with a wurtzite structure ( 6 mm) are determined using a free energy density function assuming a hexagonal parent phase (6/ mmm), with the first-order phase transition based on the dielectric stiffness relationships. The results of this analysis show that the strain sensitivity of the energy barrier is one order of magnitude larger than that of the spontaneous polarization in these wurtzite ferroelectrics, yet both are less sensitive to strain compared to classic perovskite ferroelectrics. These analysis results reported here explain experimentally reported sensitivity of the coercive field to elastic strain/stress in Al 1− x Sc x N films and would enable further thermodynamic analysis via phase field simulation and related methods. 

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3. Computational and Experimental Investigation of Chiral and Achiral Two‐Dimensional Organic Lead Bromide Perovskites: Octahedral Distortions and Electronic and Optical Properties

   https://doi.org/10.1002/cphc.202500423  

   Masud, Md Mehdi; Viera, Jarek; Ben‐Akacha, Azza; Ma, Biwu; Strubbe, David A (October 2025, ChemPhysChem)

   A computational investigation is presented, in conjunction with synthesis and experimental characterization, into the structural, electronic, and optical properties of layered two‐dimensional organic lead bromide perovskites. Materials based on the chiral (R/S)‐4‐fluoro‐α‐methylbenzylammonium (R/S‐FMBA), which have been shown to lead to bright room‐temperature circularly polarized luminescence, are contrasted with the similar achiral 4‐fluorobenzylammonium (FBA). Using density functional theory (DFT) with van der Waals (vdW) corrections, relaxed structures (compared with X‐ray diffraction, XRD) and optical absorption spectra (compared with experiments) are studied, as well as band structure and orbital character of transitions. A Python code is developed and provided to calculate octahedral distortions and compare DFT and XRD results, finding that vdW corrections are important for accuracy and that DFT overestimates octahedral tilt angles. (FMBA)₂PbBr₄shows among the largest tilt angle differences (often termed ) reported, 14°–15°, indicating strong inversion symmetry‐breaking, which enables its chiral emission. A large resulting Dresselhaus spin‐splitting effect is found. The lowest‐energy optical transitions involve the perovskite only and are polarized within the layer. This work furthers understanding of structure‐property relations with applications to optoelectronics and spintronics. 

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4. Effect of Precursor Purge Time on Plasma-Enhanced Atomic Layer Deposition-Prepared Ferroelectric Hf _0.5 Zr _0.5 O ₂ Phase and Performance

   https://doi.org/10.1021/acsomega.5c01112  

   Choi, Yong Kyu; Holsgrove, Kristina; Watson, Andrea; Aronson, Benjamin L; Lenox, Megan K; Shvilberg, Liron; Zhou, Chuanzhen; Fields, Shelby S; Wang, Shihao; McDonnell, Stephen J; et al (May 2025, ACS Omega)

   Hafnium oxide-based thin films, in particular hafnium zirconium oxide (HZO), have potential for applications in nonvolatile memory and energy harvesting. Atomic layer deposition (ALD) is the most widely used method for HZO deposition due to its precise thickness control and ability to provide conformal coverage. Previous studies have shown the effects of different metal precursors, oxidizer precursors, and process temperatures on the ferroelectric properties of HZO. However, no mechanism has been identified to describe the different phase stabilities as the metal precursor purge time varies. This study investigates how varying the metal precursor purge time during plasma-enhanced ALD (PE-ALD) influences the phases and properties of the HZO thin films. Grazing incidence X-ray diffraction, Fourier transform infrared spectroscopy, and scanning transmission electron microscopy are used to study the changes in phase of HZO with variation of the metal precursor purge time during the PE-ALD process. The phases observed are correlated with polarization and relative permittivity responses under an electric field, including wake-up and endurance effects. The resulting phases and properties are linked to changes in composition, as measured using time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. It is shown that short metal precursor purge times result in increased carbon and nitrogen impurities and stabilization of the antipolar Pbca phase. Long purge times lead to films comprising predominantly the ferroelectric Pca21 phase. 

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5. Understanding nanoscale structural distortions in Pb(Zr _0.2 Ti _0.8 )O ₃ by utilizing X-ray nanodiffraction and clustering algorithm analysis

   https://doi.org/10.1107/S1600577520013661  

   Christiansen-Salameh, Joyce; Yang, Morris; Rippy, Geoffrey; Li, Jianheng; Cai, Zhonghou; Holt, Martin; Agnus, Guillaume; Maroutian, Thomas; Lecoeur, Philippe; Matzen, Sylvia; et al (January 2021, Journal of Synchrotron Radiation)

   null (Ed.)

   Hard X-ray nanodiffraction provides a unique nondestructive technique to quantify local strain and structural inhomogeneities at nanometer length scales. However, sample mosaicity and phase separation can result in a complex diffraction pattern that can make it challenging to quantify nanoscale structural distortions. In this work, a k -means clustering algorithm was utilized to identify local maxima of intensity by partitioning diffraction data in a three-dimensional feature space of detector coordinates and intensity. This technique has been applied to X-ray nanodiffraction measurements of a patterned ferroelectric PbZr 0.2 Ti 0.8 O 3 sample. The analysis reveals the presence of two phases in the sample with different lattice parameters. A highly heterogeneous distribution of lattice parameters with a variation of 0.02 Å was also observed within one ferroelectric domain. This approach provides a nanoscale survey of subtle structural distortions as well as phase separation in ferroelectric domains in a patterned sample. 

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