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Polarization switching in ferroelectric HfO2 from first-principles lattice mode analysis

Physical Review B 2025年第13期111卷 134106-134106页

作者： Yubo Qi Sobhit Singh Karin M. Rabe Department of Physics University of Alabama at Birmingham Birmingham Alabama 35294 USA Department of Mechanical Engineering University of Rochester Rochester New York 14627 USA Materials Science Program University of Rochester Rochester New York 14627 USA Department of Physics and Astronomy Rutgers University Piscataway New Jersey 08854 USA

In this paper, we introduce a first-principles-based lattice mode analysis method to investigate the competition between different polarization switching paths in HfO2. Because the stability of the polar orthorhombic Pca21 phase of HfO2 arises from a trilinear coupling, polarization switching requires the flipping of not only the polar Γ15Z mode, but also at least one zone-boundary antipolar mode. This means that each polarization state has multiple variants, leading to multiple possible switching paths connecting up- and down-polarized states, which can be systemically enumerated within this framework for efficient identification of the optimal switching path. Our lattice mode analysis also explains why the activation energy of propagation of the most widely studied domain-wall structure in HfO2, which requires the reversal of the X2− mode, is much larger than that of propagation of domain-wall structures with a uniform sign for the X2− mode. This approach deepens our understanding of distinctive properties of ferroelectric HfO2 related to polarization switching and domain-wall motion, including sluggish domain-wall motion, robust ferroelectricity in thin films, and the observation that the antipolar Pbca phase can hardly be transformed to the ferroelectric Pca21 phase by an electric field. Our mode analysis method can be more generally applied to any improper or hybrid improper ferroelectric, in which polarization switching requires changes of nonpolar distortions, for systematic and efficient prediction of optimal switching paths and estimation of coercive fields.

关键词： Ferroelectricity

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Synergetic effects of multiple junction and surface hydroxyl in Cu/CuO/Cu2O/TiO2 heterostructures towards highly efficient photocatalysts for hydrogen generation

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materials Science for Energy Technologies 2025年 8卷 131-142页

作者： Subagyo, Riki Anindika, Garcelina Rizky Aufkani, Afif Akmal Zhang, Lei Ardhyananta, Hosta Burhan, R.Y. Perry Nugraheni, Zjahra Vianita Akhlus, Syafsir Bahruji, Hasliza Prasetyoko, Didik Wellia, Diana Vanda Ivansyah, Atthar Luqman Arramel Kusumawati, Yuly Department of Chemistry Faculty of Science and Analytic Data Institut Teknologi Sepuluh Nopember Surabaya60111 Indonesia Center of Excellence Applied Physics and Chemistry Nano Center Indonesia Jl PUSPIPTEK South Tangerang Banten15314 Indonesia Department of Physics National University of Singapore Singapore117551 Singapore Department of Materials and Metallurgical Engineering Faculty of Industrial Technology and Systems Engineering Institut Teknologi Sepuluh Nopember Surabaya60111 Indonesia Centre of Advanced Material and Energy Science Universiti Brunei Darussalam Jalan Tungku Link BE 1410 Brunei Department of Chemistry Faculty of Mathematics and Natural Sciences Universitas Andalas Padang25163 Indonesia Master Program in Computational Science Faculty of Mathematics and Natural Science Institut Teknologi Bandung Jalan Ganesha No. 10 Bandung40132 Indonesia Instrumentation and Computational Physics Research Group Department of Physics Faculty of Mathematics and Natural Sciences Institut Teknologi Bandung Jalan Ganesha No.10 West Java Bandung40132 Indonesia

The implementation of titanium dioxide (TiO2) as a photocatalyst material in hydrogen (H2) evolution reaction (HER) has embarked renewed interest in the past decade. Rapid electron-hole pairs recombination and wide band gap of a photo-sensitive material of TiO2 are detrimental toward the targeted catalytical reaction. In this study, we present the rational design, fabrication, photocatalytic performance of TiO2-Cu/CuO/Cu2O heterostructures (CuTi) using viable chemical reduction method. The Z-scheme and S-scheme are succesfully generated across the TiO2/CuO/Cu2O interfaces, while the Schottky junction arises on the Cu perimeters. This is evidenced from the blue shifted about 0.3 eV of Cu 2p core level determined by using X-ray photoemission spectroscopy (XPS), in combination with the formation of inverse V-shape of the Mott-Schottky plots. In addition, we find that Cu/CuO/Cu2O facilitates photon absorption range up to the visible region. The multiple heterojunction and the large number of OHsurface enhanced charge carrier transfer are associated to the suppression of photoluminescence (PL) intensity, high surface hydroxyl (OHsurface) density in CuTi probed by XPS, and fast electron transfer based on the electrochemical measurements. The presence of OHsurface inhibits the recombination of electron. A significant H2 photogeneration rate enhancement is achieved when an optimized 5 wt% Cu/CuO/Cu2O concentration is used on TiO2 to achieve 7,157.19 μmol·g−1 (1,789.30 μmol·g−1·h−1). Based on this finding, zero emission energy innitiative could be materialized under multiple heterojunctions in photocatalytic process is beneficial for enhancing the H2 production. © 2025 The Authors

关键词： Titanium dioxide

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Unavoidable multilevel biaxial symmetry breaking in chiral hybrid liquid crystals

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Physical Review E 2025年第4期111卷 045410-045410页

作者： Jin-Sheng Wu Marina Torres Lázaro Souvik Ghosh Haridas Mundoor Henricus H. Wensink Ivan I. Smalyukh Department of Physics and Chemical Physics Program University of Colorado Boulder Colorado 80309 USA Laboratoire de Physique des Solides–UMR 8502 Université Paris-Saclay and CNRS 91405 Orsay France International Institute for Sustainability with Knotted Chiral Meta Matter Hiroshima University Higashihiroshima Japan Department of Electrical Computer and Energy Engineering Materials Science and Engineering Program and Soft Materials Research Center University of Colorado Boulder Colorado 80309 USA Renewable and Sustainable Energy Institute National Renewable Energy Laboratory and University of Colorado Boulder Colorado 80309 USA

Chiral nematic or cholesteric liquid crystals (LCs) are fluid mesophases with long-ranged orientational order featuring a quasilayered periodicity imparted by a helical director configuration but lacking long-range positional order. Doping molecular cholesteric LCs with strongly anisotropic uniaxial colloidal particles adds another level of complexity because of the interplay between weak surface-anchoring boundary conditions and bulk-based elastic distortions near the particle-LC interface. Using cylindrical colloidal disks and rods with different geometric shapes and surface conditions, we demonstrate that these colloidal inclusions generically exhibit biaxial orientational probability distributions which may impart anomalously strong local biaxiality onto the hybrid cholesteric LC structure. Unlike nonchiral hybrid molecular-colloidal LCs, where biaxial order emerges only at critical colloid volume fractions exceeding some uniaxial-biaxial transition value, the orientational probability of the colloidal inclusions immersed in chiral nematic hosts is unambiguously biaxial even at infinite dilution. We demonstrate that the colloids induce local biaxial perturbations within the molecular orientational order of the LC host medium which strongly enhances the weak but native biaxial order of chiral nematic LC induced by the chiral symmetry breaking of the director field. With the help of analytical modeling and computer simulations based on the Landau–de Gennes free energy of the host LC around the colloids, we rationalize the observed multilevel biaxial order and conclude that it is not only unavoidable but also strongly enhanced compared to both achiral hybrid LCs and purely molecular cholesteric LCs.

关键词： Cholesteric liquid crystals

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Bandgap of Epitaxial Single-Crystal BiFe1−xMnxO3 Films Grown Directly on SrTiO3/Si(001)

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materials 2025年第9期18卷 2022-2022页

作者： Cantrell, Samuel R. Miracle, John T. Cottier, Ryan J. Lindsey, Skyler Theodoropoulou, Nikoleta Materials Science Engineering and Commercialization Program Texas State University San MarcosTX78666 United States Department of Physics Texas State University San MarcosTX78666 United States

We report the growth and optical characterization of single-crystal BiFe1−xMnxO3 thin films directly on SrTiO3/Si(001) substrates using molecular beam epitaxy. X-ray diffraction confirmed epitaxial growth, film crystallinity, and sharp interface quality. Scanning electron microscopy and energy dispersive X-ray spectroscopy verified uniform film morphology and successful Mn incorporation. Spectroscopic ellipsometry revealed a systematic bandgap reduction with increasing Mn concentration, from 2.7 eV in BiFeO3 to 2.58 eV in BiFe0.74Mn0.26O3, consistent with previous reports on Mn-doped BiFeO3. These findings highlight the potential of BiFe1₋xMnxO3 films for bandgap engineering, advancing their integration into silicon-compatible multifunctional optoelectronic and photovoltaic applications. © 2025 by the authors.

关键词： Molecular beam epitaxy

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Large negative magnetoresistance in the off-stoichiometric topological semimetal PrSbxTe2−x

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Physical Review B 2025年第2期111卷 024421-024421页

作者： Gokul Acharya Krishna Pandey M. M. Sharma Jian Wang Santosh Karki Chhetri Md Rafique Un Nabi Dinesh Upreti Rabindra Basnet Josh Sakon Department of Physics University of Arkansas Fayetteville Arkansas 72701 USA Materials Science and Engineering Program Institute for Nanoscience and Engineering University of Arkansas Fayetteville Arkansas 72701 USA Department of Chemistry and Biochemistry Wichita State University Wichita Kansas 67260 USA Department of Chemistry & Physics University of Arkansas at Pine Bluff Pine Bluff Arkansas 71603 USA Department of Chemistry and Biochemistry University of Arkansas Fayetteville Arkansas 72701 USA

Magnetic topological materials LnSbTe (Ln = lanthanide) have attracted intensive attention because of the presence of interplay between magnetism, topological, and electron correlations depending on the choices of magnetic Ln elements. Varying Sb and Te composition is an efficient approach to control structural, magnetic, and electronic properties. Here, we report on the composition-dependent properties in PrSbxTe2−x. We identified the tetragonal-to-orthorhombic structure transitions in this material system and very large negative magnetoresistance in the x=0.3 composition, which might be ascribed to the coupling between magnetism and transport. Such unusual magnetotransport enables PrSbxTe2−x topological materials as a promising platform for device applications.

关键词： Magnetoresistance

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Three-dimensional construction of hyperuniform, nonhyperuniform, and antihyperuniform disordered heterogeneous materials and their transport properties via spectral density functions

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Physical Review E 2025年第3期111卷 035310-035310页

作者： Wenlong Shi Yang Jiao Salvatore Torquato Materials Science and Engineering Arizona State University Tempe Arizona 85287 USA Department of Physics Arizona State University Tempe Arizona 85287 USA Department of Chemistry Princeton University Princeton New Jersey 08544 USA Department of Physics Princeton University Princeton New Jersey 08544 USA Princeton Institute of Materials Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

Rigorous theories connecting physical properties of a heterogeneous material to its microstructure offer a promising avenue to guide the computational material design and optimization. The spectral density function χ̃V(k), which can be obtained experimentally from scattering data, enables accurate determination of various transport and wave propagation characteristics, including the time-dependent diffusion spreadability S(t) and effective dynamic dielectric constant εe for electromagnetic wave propagation. Moreover, χ̃V(k) determines rigorous upper bounds on the fluid permeability K. Given the importance of χ̃V(k), we present here an efficient Fourier-space based computational framework to construct three-dimensional (3D) statistically isotropic two-phase heterogeneous materials corresponding to targeted spectral density functions. In particular, we employ a variety of analytical functional forms for χ̃V(k) that satisfy all known necessary conditions to construct disordered stealthy hyperuniform, standard hyperuniform, nonhyperuniform, and antihyperuniform two-phase heterogeneous material systems at varying phase volume fractions. We show that by tuning the correlations in the system across length scales via the targeted functions, one can generate a rich spectrum of distinct structures within each of the above classes of materials. Importantly, we present the first realization of antihyperuniform two-phase heterogeneous materials in 3D, which are characterized by autocovariance function χV(r) with a power-law tail, resulting in microstructures that contain clusters of dramatically different sizes and morphologies. We also determine the diffusion spreadability S(t) and estimate the fluid permeability K associated with all of the constructed materials directly from the corresponding spectral densities. Although it is well established that the long-time asymptotic scaling behavior of S(t) only depends on the functional form of χ̃V(k), with the stealthy hyperuniform a

关键词： Spectral density

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Sodium niobate with high photocatalytic activity for the removal of organic dye and inactivation of Escherichia coli, Staphylococcus aureus, and Klebsiella pneumoniae bacteria: the effect of Zn doping on these properties

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Ceramics International 2025年

作者： Fernandes, Daiane Raubach, Cristiane Trassante, Carla Dias, Vagner Melo, Luize Silveira, Marcelle Carvalho, Ramon Moreira, Mario Jardim, Pedro Ferrer, Mateus Giongo, Janice Vaucher, Rodrigo Longo, Elson Cava, Sergio Post-Graduate Program in Materials Science and Engineering Federal University of Pelotas RS Pelotas96010-610 Brazil Post-Graduate Program in Microbiology and Parasitology Federal University of Pelotas RS Capão do Leão96160-000 Brazil Post-Graduate Program in Physics Federal University of Pelotas RS Capão do Leão96160-000 Brazil Functional Materials Development Center São Carlos Federal University SP São Carlos13565-905 Brazil

NaNbO3 doped with Zn (0.00, 0.02, and 0.05 mmol) was synthesized by the microwave-assisted hydrothermal method. Photocatalytic and antibacterial activities were investigated. X-ray diffraction revealed the coexistence of two orthorhombic symmetries (P21ma and Pbma), with doping promoting a progressive increase in the Pbma fraction. All samples exhibited a fiber-like shape (diameter of ∼200 nm), which remained unchanged with doping. The low Zn content (0.02 mmol) reduced the band gap energy from 3.08 to 2.95 eV. As a result, this sample exhibited superior photocatalytic activity, achieving 100 % RhB dye degradation within 45 min, under UV light. Scavenger tests revealed that hydroxyl radicals, holes, and superoxide radical anions were the main active species involved in the photocatalytic reaction. Additionally, the photocatalyst demonstrated excellent recyclability over three consecutive cycles. Pure NaNbO3 exhibited strong antibacterial activity, completely inhibiting the growth of S. aureus, E. coli, and K. pneumoniae at the tested concentrations. Although the Zn-doped sample also demonstrated antibacterial action, the response was concentration-dependent. This study is the first report on Zn doping in NaNbO3, as well as the first investigation of its antibacterial activity against K. pneumoniae and S. aureus. © 2025 Elsevier Ltd and Techna Group S.r.l.

关键词： Escherichia coli

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Long-range order of polygonal grain boundaries

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Physical Review B 2025年第4期111卷 045103-045103页

作者： N. Sarkar P. R. Bandaru R. C. Dynes Department of Mechanical Engineering University of California San Diego La Jolla California 92093-0411 USA Program in Materials Science University of California San Diego La Jolla California 92093-0411 USA Department of Physics University of California San Diego La Jolla California 92093-0411 USA

Atomic-scale spatial resolution was achieved in the mapping and spectroscopy of polygonal grain boundaries (GBs) on atomically flat highly oriented pyrolytic graphite using scanning tunneling microscopy (STM). These GBs are long-range ordered one-dimensional periodic structures comprising pentagon-heptagon pairs. A comprehensive study combining local electronic, valleytronic, mechanical, and topological properties is conducted on this GB which reveals the interplay between these properties. On the atoms and bonds of individual GB polygons, spatially localized conductance states were probed, in addition to edge states. The spatial extent of these states was observed on GB by bias-dependent imaging. The electron scattering angle at the GB edges was also modulated with a sample bias which exhibited valley flipping and unique quantum interference effects such as backscattering and intervalley scattering. In situ strain-induced mechanical and electronic modifications were observed through surface deformation caused by the STM tip, revealing flattened electronic energy band dispersion and shifts in carrier doping.

关键词： Grain boundaries

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Structural properties of hyperuniform Voronoi networks

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Physical Review E 2025年第3期111卷 034123-034123页

作者： Eli Newby Wenlong Shi Yang Jiao Reka Albert Salvatore Torquato Department of Physics Pennsylvania State University University Park Pennsylvania 16802 USA Materials Science and Engineering Arizona State University Tempe Arizona 85287 USA Department of Physics Arizona State University Tempe Arizona 85287 USA Department of Chemistry Princeton University Princeton New Jersey 08544 USA Department of Physics Princeton University Princeton New Jersey 08544 USA Princeton Institute of Materials Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA

Disordered hyperuniform many-particle systems are recently discovered exotic states of matter, characterized by the complete suppression of normalized infinite-wavelength density fluctuations, as in perfect crystals, while lacking conventional long-range order, as in liquids and glasses. In this work, we begin a program to quantify the structural properties of nonhyperuniform and hyperuniform networks. In particular, large two-dimensional (2D) Voronoi networks (graphs) containing approximately 10,000 nodes are created from a variety of different point configurations, including the antihyperuniform hyperplane intersection process (HIP), nonhyperuniform Poisson process, nonhyperuniform random sequential addition (RSA) saturated packing, and both non-stealthy and stealthy hyperuniform point processes. We carry out an extensive study of the Voronoi-cell area distribution of each of the networks by determining multiple metrics that characterize the distribution, including their average areas and corresponding variances as well as higher-order cumulants (i.e., skewness γ1 and excess kurtosis γ2). We show that the HIP distribution is far from Gaussian, as evidenced by a high skewness (γ1=3.16) and large positive excess kurtosis (γ2=16.2). The Poisson (with γ1=1.07 and γ2=1.79) and non-stealthy hyperuniform (with γ1=0.257 and γ2=0.0217) distributions are Gaussian-like distributions, since they exhibit a small but positive skewness and excess kurtosis. The RSA (with γ1=0.450 and γ2=−0.0384) and the highest stealthy hyperuniform distributions (with γ1=0.0272 and γ2=−0.0626) are also non-Gaussian because of their low skewness and negative excess kurtosis, which is diametrically opposite of the non-Gaussian behavior of the HIP. The fact that the cell-area distributions of large, finite-sized RSA and stealthy hyperuniform networks (e.g., with N≈10,000 nodes) are narrower, have larger peaks, and smaller tails than a Gaussian distribution implies that in the thermodynamic limit th

关键词： Gaussian distribution

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Thermo-optical properties of erbium-doped germanate-bismuth glasses

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Optical materials 2025年 166卷

作者： Silva, Adriano Almeida Lima, Lucas Batista Silva da Silva, Isis Lee Garcia, Hans Anderson Bell, Maria José Valenzuela Kassab, Luciana Reyes Pires Santos, Francisco Eroni Paz Postgraduate Program in Physics Federal University of Piauí PI 64049550 Brazil Department of Physics Federal University of Juiz de Fora MG Juiz de Fora36036-900 Brazil Faculdade de Tecnologia São Paulo CEETEPS SP São Paulo01124060 Brazil Postgraduate Program in Engineering and Materials Science Federal University of Teresina PI 64049550 Brazil

In this study, we investigate the thermo-optical properties of GeO2–Bi2O3 glasses doped with different concentrations of rare earth ions by thermal lens technique;UV-VIS and photoluminescence (PL) spectroscopy, as well as measurements of thermal diffusivity, thermal conductivity and quantum efficiency, are presented aiming at potential photonic applications. High infrared fluorescence lifetimes around 4 ms and quantum efficiencies of ∼80 % for 1 % Er3+ concentration, determined via lifetime and thermal lens methods, enabled efficient laser operation. Positive ds/dT values confirmed the self-focusing nature beneficial for high-power systems. While quantum efficiencies decreased exponentially with rising Er3+ due to non-radiative relaxation from erbium-matrix interactions, reasonably high efficiencies above 74 % persisted at 1 % doping. The thermal diffusivity and conductivity exhibited little changes with varying Er3+ concentration and showed to be matrix dependent. © 2025 Elsevier B.V.

关键词： Quantum efficiency

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