Local Structural Correlations Research Articles

Superconducting transition of GdBa2Cu3O7-x/La0.7A0.3MnO3 (A=Sr and Ca) bilayers governed by tunable interlayer structural coupling

Bilayers composed of high-Tc cuprate superconductors (HTS) with manganites have garnered significant attention due to the complex interaction between two layers, leading to competition among various ordering phenomena. When HTS and manganties are interfaced, new functionalities can emerge that are absent in the individual components. Notably, epitaxial strain can alter crystal structures and electronic states, significantly impacting superconductivity in HTS/manganite heterostructures. In this study, we analyze the superconducting and ferromagnetic behaviors of GdBa2Cu3O7-x(GdBCO)/La0.7A0.3MnO3(LAMO, where A=Sr and Ca) bilayers, maintain a constant GdBCO thickness of 500 nm while varying the LAMO thickness from 25 to 100 nm. We focus on the local structural correlations between the two layers. Temperature-dependent EXAFS spectra were systematically measured at the Cu and Mn K-edges to investigate the local atomic structures of both layers across the superconducting transition temperature (Tc). Our spectroscopic measurements reveal distinct conformations of the MnO6 octahedra near Tc, which are absent in single-layer LSMO, indicating structural coupling between the layers. Additionally, our magnetization studies show a strong relationship between the structural coupling, magnetic anisotropy (MA), and the superconducting transition of the GdBCO/LAMO bilayers. The additional distortion of the MnO6 octahedra in the GdBCO/LAMO bilayer, likely stemming from structural coupling, may account for the changes in the superconducting transition associated with magnetic anisotropy. This modification of structural coupling can be controlled by adjusting the LAMO thickness, yet it remains highly dependent on the bond geometry of LAMO. The Mn-O bond in LCMO is stiffer than in LSMO, resulting in a smaller change in structural coupling with varying thickness in LCMO compared to LSMO. The disparity in structural coupling directly impacts the magnetic properties of the LAMO layer and subsequently influences the superconducting property ΔTc. Our findings highlight the significance of structural coupling as a critical factor affecting the superconductivity of GdBCO/LAMO bilayers. Furthermore, this study provide foundational insight for designing various applications, such as magnetic sensors and spintronic devices, by enhancing our understanding of local dynamics at the interface between ferromagnets and superconductors.

Correction to “Size Dependence of the Local Structure and Atomic Correlations in Tellurium Nanoparticles”

Correction to “Size Dependence of the Local Structure and Atomic Correlations in Tellurium Nanoparticles”

Pressure-induced antiferromagnetic-tetragonal to nonmagnetic-collapse-tetragonal insulator-metal transition in ThMnAsN

We report first-principles numerical discovery of hydrostatic pressure-driven tetragonal to collapsed tetragonal transition in 1111-type material ThMnAsN accompanied by simultaneous magneto-structural, insulator to metal transition together with complete collapse of Mn moments. We present detailed evolution of various structural parameters, magnetism and electronic structures of ThMnAsN with increasing hydrostatic pressure. All the structural parameters show anomalies at a critical pressure $$P_\text {c} \sim$$ 8.1 GPa; c-lattice parameter, out-of-plane As–As bond length, anion height ( $$h_\text {As}$$ ) undergo drastic modifications compared to the in-plane parameters which is manifested in an iso-structural phase transition from tetragonal to a collapsed tetragonal (cT) phase. These modifications in “local structural correlations” due to pressure destroy the usually localized nature of Mn moments which gets completely quenched. Apart from that the elastic constant, the electronic structures also bear the finger prints of insulator-metal and magneto-structural transition at higher pressures accompanying a total collapse of magnetic moment at the vicinity of $$P_\text {c}$$ . The critical value of the pressure $$P_\text {c}$$ at which tetragonal to collapse tetragonal phase transition occurs, remains robust with respect to the on-site Hubbard correlation (U). The dynamical stability of the compound at higher pressures (above and below the magneto-structural transition) is affirmed through detailed computations of phonon dispersion curves endowed with positive phonon frequency throughout the Brillouin zone. The effect of magnetic spin structure on the electronic band structures is obtained through band unfolding. The electronic structure of ThMnAsN at higher pressures “orbital selectively” influences bands, band gap and closely resembles with the electronic structure of Fe-based superconductors (quasi-two-dimensional Fermi surfaces) with the occurrences of orbital-selective Lifshitz transition.

Reconstruction based on adaptive group least angle regression for fluorescence molecular tomography.

Fluorescence molecular tomography can combine two-dimensional fluorescence imaging with anatomical information to reconstruct three-dimensional images of tumors. Reconstruction based on traditional regularization with tumor sparsity priors does not take into account that tumor cells form clusters, so it performs poorly when multiple light sources are used. Here we describe reconstruction based on an "adaptive group least angle regression elastic net" (AGLEN) method, in which local spatial structure correlation and group sparsity are integrated with elastic net regularization, followed by least angle regression. The AGLEN method works iteratively using the residual vector and a median smoothing strategy in order to adaptively obtain a robust local optimum. The method was verified using numerical simulations as well as imaging of mice bearing liver or melanoma tumors. AGLEN reconstruction performed better than state-of-the-art methods with different sizes of light sources at different distances from the sample and in the presence of Gaussian noise at 5-25%. In addition, AGLEN-based reconstruction accurately imaged tumor expression of cell death ligand-1, which can guide immunotherapy.

Local structure of liquid oxygen up to supercritical conditions from ab initio pair potentials

The local structure and orientational correlations (OCs) of liquid oxygen up to supercritical conditions have been determined using highly accurate ab initio pair potentials and a spin-average approximation. The predicted radial distribution functions are in excellent agreement with all the available experimental data covering a wide range of temperatures and pressures. The elusive shoulder characteristic of several diatomic fluids is accurately reproduced and, more importantly, its true origin elucidated by performing an exhaustive analysis of the OCs, indicating the relevance of specific configurations.

Mapping structural correlations in real space.

An analysis of neutron and x-ray diffuse scattering from yttria-stabilized zirconia by Schmidt et al. [Acta Cryst. (2023), B79, 137-147] uses three-dimensional pair-distribution functions (3D-ΔPDF) to determine local structural correlations without the need for sophisticated modeling.

CMAN: Leaning Global Structure Correlation for Monocular 3D Object Detection

The key to 3D object detection is proper utilization of depth data. Compared with LiDAR based approaches, 3D object detection from a single image remains a challenging task due to the lack of structure information. Recent methods leverage monocular depth estimation as a way to produce 2D depth maps, and adopt the depth maps as additional source of input to explore structure information. However, these methods either encode local structure correlations, or encode long range structure correlations by iteratively passing local messages. In this work, we propose a cross modal attention network (CMAN) for monocular 3D object detection. It is built upon the self-attention module which learns attention map from single modal data. Our CMAN is able to encode structure correlations from depth data, and embed the structure correlations with appearance information which is learned from RGB data. Thanks to the attention learning mechanism, our CMAN learns global structure correlations without iteration. In order to reduce the computational burden, our CMAN adopts a novel node sampler to eliminate redundant nodes during the attention map calculation. Experiment results on benchmark KITTI3D dataset show that our proposed CMAN outperforms the state-of-the-art methods.

Phase behaviour of ammonium bromide-d 4 under high pressure and low temperature; an average and local structure study

We revisit the pressure-induced order–disorder transition between phases II and IV in ammonium bromide-d 4 using neutron diffraction measurements to characterise both the average and local structures. We identify a very sluggish transition that does not proceed to full conversion and local structure correlations indicate a slight preference for ammonium cation ordering along ⟨110⟩ crystallographic directions, as pressure is increased. Simultaneous cooling below ambient temperature appears to facilitate the pressure-induced transition. Variable-temperature, ambient-pressure measurements across the IV → III → II transitions show slower conversion than previously observed, and that phase III exhibits metastability above ambient temperature.

Microscopic origin of giant piezoelectricity in ferroelectric xBi(Ni0.5Hf0.5)O3−(1−x)PbTiO3 beyond the morphotropic phase boundary

Local structural correlations in a novel ferroelectric solid solution [$x\mathrm{Bi}({\mathrm{Ni}}_{0.5}{\mathrm{Hf}}_{0.5}){\mathrm{O}}_{3}\text{\ensuremath{-}}(1\ensuremath{-}x){\mathrm{PbTiO}}_{3}$ at $x=0.39$] have been drawn out through atomistic modeling against neutron pair distribution functions and complementary Raman scattering measurements. By examining polar displacements of different cations from the refined structural models, we reveal the distributions of cation-specific dipolar fluctuations at the key composition where the maximum piezoelectric response was recorded. It becomes clear that the unusual structural modifications observed after the poling are simply a manifestation driven by the varying extent of the dipolar fluctuations and not a structural transformation caused by adaptive cationic displacements. Moreover, in addition to strong dipolar flexibility under an electric field, both poled and unpoled ceramics exhibit orientation-independent polarized Raman scattering, which is more typical of a dipolar glass with a responsive and polarizable matrix than a polycrystalline material composed of ferroelectric domains. Therefore, compared to other analogous $x\mathrm{Bi}(\mathrm{Me}){\mathrm{O}}_{3}\text{\ensuremath{-}}(1\ensuremath{-}x){\mathrm{PbTiO}}_{3}$ systems, the current material is a unique case where chemical substitution has led to a highly polarizable ionic-covalent matrix that seems to be the key ingredient to generate giant piezoelectricity at a composition beyond the morphotropic phase boundary.

Experimental test of a predicted dynamics–structure–thermodynamics connection in molecularly complex glass-forming liquids

Understanding in a unified manner the generic and chemically specific aspects of activated dynamics in diverse glass-forming liquids over 14 or more decades in time is a grand challenge in condensed matter physics, physical chemistry, and materials science and engineering. Large families of conceptually distinct models have postulated a causal connection with qualitatively different "order parameters" including various measures of structure, free volume, thermodynamic properties, short or intermediate time dynamics, and mechanical properties. Construction of a predictive theory that covers both the noncooperative and cooperative activated relaxation regimes remains elusive. Here, we test using solely experimental data a recent microscopic dynamical theory prediction that although activated relaxation is a spatially coupled local-nonlocal event with barriers quantified by local pair structure, it can also be understood based on the dimensionless compressibility via an equilibrium statistical mechanics connection between thermodynamics and structure. This prediction is found to be consistent with observations on diverse fragile molecular liquids under isobaric and isochoric conditions and provides a different conceptual view of the global relaxation map. As a corollary, a theoretical basis is established for the structural relaxation time scale growing exponentially with inverse temperature to a high power, consistent with experiments in the deeply supercooled regime. A criterion for the irrelevance of collective elasticity effects is deduced and shown to be consistent with viscous flow in low-fragility inorganic network-forming melts. Finally, implications for relaxation in the equilibrated deep glass state are briefly considered.

Hyperspectral Band Selection Based on Adaptive Neighborhood Grouping and Local Structure Correlation

Band selection is a direct and effective dimension reduction method and is one of the hotspots in hyperspectral remote sensing research. However, most of the methods ignore the orderliness and correlation of the selected bands and construct band subsets only according to the number of clustering centers desired by band sequencing. To address this issue, this article proposes a band selection method based on adaptive neighborhood grouping and local structure correlation (ANG‐LSC). An adaptive subspace method is adopted to segment hyperspectral image cubes in space to avoid obtaining highly correlated subsets. Then, the product of local density and distance factor is utilized to sort each band and select the desired cluster center number. Finally, through the information entropy and correlation analysis of bands in different clusters, the most representative bands are selected from each cluster. Regarding evaluating the effectiveness of the proposed method, comparative experiments with the state‐of‐the‐art methods are conducted on three public hyperspectral datasets. Experimental results demonstrate the superiority and robustness of ANG‐LSC.

Adaptive dipolar correlation in ferroelectric x(Ba0.7Ca0.3)TiO3−(1−x)Ba(Zr0.2Ti0.8)O3

Deriving structure-property relationships for multicomponent ferroelectric materials has always been a challenging problem because the properties are mostly driven by subtle nanoscale correlations which are hard to detect. Here we have studied the famous Pb-free material $x({\mathrm{Ba}}_{0.7}{\mathrm{Ca}}_{0.3}){\mathrm{TiO}}_{3}\text{\ensuremath{-}}(1\ensuremath{-}x)\mathrm{Ba}({\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}){\mathrm{O}}_{3}$ $(x\mathrm{BCT}\text{\ensuremath{-}}\mathrm{BZT})$ which has been at the center of attention for approximately the last 10 years because of its unprecedented piezoelectric properties. However, the structure-property relationship for $x\mathrm{BCT}$-BZT remains elusive as neither the common concepts nor the experimental results lead to satisfactory models which can fully explain its unusual piezoelectric properties as a function of composition as well as recognize its uniqueness compared to other similar systems. Hence we have applied total neutron-scattering and Raman-scattering methods to examine the local structural correlations of $x\mathrm{BCT}$-BZT in the range $0.40\ensuremath{\le}x\ensuremath{\le}0.60$ at ambient conditions. By refining large-box atomistic models against the neutron pair distribution functions, we have observed an emerging coherence in the polar displacements of the cations at $x=0.50$, leading to an increased structural ergodicity at the key orthorhombic-tetragonal phase boundary. Given the very similar level of local structural disorder and spontaneous polarization found in the system with $x$, we propose that the abrupt amplification of piezoelectric properties in this material at a region of phase instability is a consequence of enhanced collaboration amongst the all cations in a strain-reduced local environment. It also indicates that the popular structure-property concept entailing a low-symmetry crystal structure cannot be a generic concept or a precondition.

Structural studies on fluid Hg and fluid Se at high temperatures and high pressures by means of X-ray diffraction and small angle X-ray scattering

Abstract X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) measurements for fluid Hg and fluid Se up to the supercritical region have been carried out using synchrotron radiation at SPring-8. We obtained the structure factor, S ( Q ) $S\left(Q\right)$ , including a small angle region, and the pair distribution function, g ( r ) $g\left(r\right)$ , for both fluids from the liquid to the dense vapor region. Change of the local structure and medium-range correlations at the metal-insulator transition in fluid Hg were revealed. On the other, the average coordination number of two was preserved at the semiconductor-metal transition in fluid Se. From a SAXS experiment of fluid Se in 2012, SAXS spectra near the semiconductor-metal transition region show the Ornstein–Zernike profile and the SAXS intensity is reduced with increasing pressure. These results indicate difficulties of separating fluctuations intrinsic to the semiconductor-metal transition from those arising from the liquid-vapor critical point in fluid Se, although fluctuations intrinsic to the electronic transitions are largely expected in both fluids.

Correlated N/O anion orders in melilite phosphors

The N/O anion distributions in the melilite-type phosphor host material Y2Si3O3N4 and a Ce-doped sample Y1.5Ce0.5Si3O3N4 have been determined from powder neutron diffraction. Both materials have a highly ordered N/O distribution that is not changed significantly by the disorder introduced by Ce doping. This distribution evidences the presence of SiN3O and SiN2O2 tetrahedra and although these are not fully long range-ordered, local structural correlations follow simple connectivity rules that lead to an estimated residual molar entropy of R ln3. A broad range of N/O environments is found around 8-coordinate Y(Ce) sites which is expected to broaden their spectroscopic features.

Bottom-up derived flexible water model with dipole and quadrupole moments for coarse-grained molecular simulations.

Coarse-grained water models offer opportunities to study the molecular processes in water on spatial and temporal scales inaccessible to conventional atomic-level simulations. Such a model that can accurately describe the structural, electrostatic and thermodynamic properties of liquid water is difficult to derive but invaluable. Here, we present FlexDQ, a flexible three-site coarse-grained model, representing clusters of water molecules. This model was derived using a full bottom-up approach in which atomistic information of water molecules is processed using clustering techniques based on considerations of both energy and geometry and a mapping algorithm that encodes information of dipole and quadrupole moments of water clusters into coarsely grained interaction sites. Parameterization of FlexDQ was conducted consistently and systematically, augmented by these data. The resulting model reproduces not only dipolar and quadrupolar fluctuations of water clusters, but also their local structural correlations in the bulk phase and, to a good extent, pressure-related properties, dielectric permittivity and water-air interfacial properties that were not targeted for parameterization. The ability of our model to reproduce various properties of water has been shown to originate from its explicit treatment of electrostatics. Coupled with the popular MARTINI CG model, FlexDQ captures the entropy-enthalpy balance of hydrophobic interactions and describes the dielectric behavior of water at the water-membrane interface, yielding a positive internal electrostatic potential in membranes, which is otherwise difficult to reproduce using MARTINI alone. Together, the FlexDQ model and its development framework reported here show promise for studies on the biomolecules in water.

The local structure and magnetic correlations in La(Fe1-xMnx)AsO system

The local structure of La(Fe1-xMnx)AsO, showing suppression of long-range magnetic order by Mn-substitution, has been studied. Extended X-ray absorption fine structure (EXAFS) measurements at As K-edge and Fe K-edge are used to probe the atomic correlations in the FeAs-layer. We have found that both Fe-As and Fe-Fe bondlengths tend to increase with increasing Mn concentration. The associated mean square relative displacements (MSRD) reveal a gradual increase indicating increased local disorder in the FeAs-layer with Mn content. The results reveal that the FeAs-layer thickness, measured by the As-height (hAs) from the Fe-Fe plane, is correlated with the Néel temperature. Furthermore, Fe Kβ X-ray emission spectroscopy (XES) shows a sharp increase in the Fe local magnetic moment with Mn substitution. The importance of the FeAs layer thickness in describing magnetic correlations in La(Fe1−xMnx)AsO is discussed.

Pd local structure and size correlations to the activity of Pd/TiO2 for photocatalytic reforming of methanol.

The interaction between Pd and TiO2 for promoting photocatalytic activity was investigated by tailoring the size of Pd nanoparticles and monitoring the photocatalytic activity of methanol photo-reforming reaction for hydrogen gas production. We show that at 0.6 wt% Pd loading, the catalyst with highly dispersed nanoparticles obtained at 1 °C temperature exhibits superior photocatalytic activity for hydrogen gas production. At different weights of Pd loading, tailoring two sets of catalysts with different structural properties provides correlation between the changes in the Pd local structures and the rate of hydrogen production. The impact of controlling the structural properties of metal nanoparticles on influencing H2 production outweighs the effect of metal loading variation. The differences of Pd/TiO2 activity at the different metal loadings were correlated with the changes in the Pd local structure consequently affecting the electronic transfer and photocatalytic efficiency.

Temperature dependence of the ultrafast vibrational echo spectroscopy of OD modes in liquid water from first principles simulations.

The rate of vibrational spectral diffusion of OD/OH stretch modes of water is known to be interconnected with the hydrogen bond rearrangement dynamics in aqueous media as found in several recent experiments and molecular simulations. In the present study, the temperature dependence of vibrational spectral diffusion of OD stretch modes in liquid water is investigated from first principles by using the method of ab initio molecular dynamics. Kinetic rates obtained from the frequency time correlation function (FTCF), the slope of the 3-pulse photon echo (S3PE) and local structure correlation functions are used in the Arrhenius equation to determine the energy barrier for hydrogen bond rearrangement in liquid water. The slope of the 3-pulse photon echo is determined within the cumulant and Condon approximations. Although the trend found at the low temperature is slightly non-Arrhenius, the barrier for hydrogen bond rearrangement is found to be around 4.2 kcal mol-1 from all the metrics considered here. It is in good agreement with the hydrogen bond energy determined from different experiments and theoretical studies. Based on the findings, a strong correlation between the vibrational spectral diffusion timescale and hydrogen bond dynamics is identified, which gets even more pronounced at low temperatures. Spatio-temporal correlations between frequency fluctuations and the local hydrogen bond network are also explored.

Spatial–Spectral Total Variation Regularized Low-Rank Tensor Decomposition for Hyperspectral Image Denoising

Several bandwise total variation (TV) regularized low-rank (LR)-based models have been proposed to remove mixed noise in hyperspectral images (HSIs). These methods convert high-dimensional HSI data into 2-D data based on LR matrix factorization. This strategy introduces the loss of useful multiway structure information. Moreover, these bandwise TV-based methods exploit the spatial information in a separate manner. To cope with these problems, we propose a spatial–spectral TV regularized LR tensor factorization (SSTV-LRTF) method to remove mixed noise in HSIs. From one aspect, the hyperspectral data are assumed to lie in an LR tensor, which can exploit the inherent tensorial structure of hyperspectral data. The LRTF-based method can effectively separate the LR clean image from sparse noise. From another aspect, HSIs are assumed to be piecewisely smooth in the spatial domain. The TV regularization is effective in preserving the spatial piecewise smoothness and removing Gaussian noise. These facts inspire the integration of the LRTF with TV regularization. To address the limitations of bandwise TV, we use the SSTV regularization to simultaneously consider local spatial structure and spectral correlation of neighboring bands. Both simulated and real data experiments demonstrate that the proposed SSTV-LRTF method achieves superior performance for HSI mixed-noise removal, as compared to the state-of-the-art TV regularized and LR-based methods.

Stochastic Polarization Instability in PbTiO3

Although discussions of structural phase transitions in prototypical ferroelectric systems with the perovskite structure, such as BaTiO_{3} and PbTiO_{3}, started almost seventy years ago, an atomic-level description of the polar characteristics as a function of temperature, pressure, and composition remains topical. Here we provide a novel quantitative description of the temperature-driven local structural correlations in PbTiO_{3} via the development of characteristic relative cationic shifts. The results give new insights into the phase transition beyond those reliant on the long-range order. The ferroelectric-to-paraelectric transition of PbTiO_{3} is realized by the extent of a stochastic polarization instability driven by a progressive misalignment instead of a complete disappearance of the local dipoles, which further suggests that such polarization instability is chemically induced at the morphotropic phase boundary of PbTiO_{3}-based solid solutions with giant piezoelectric effect. As such, our results not only identify the evolving atomistic disorder in a perovskite-based ferroelectric system, but also suggest that polarization instability can serve as a generic fingerprint for phase transitions as well as for better understanding structure-property relationships in PbTiO_{3}-based ferroelectric solid solutions.