Crystal Symmetry Research Articles

Crystal structure of heteroepitaxial BaTiO3–KNbO3 core–shell nanocomposite particles studied by synchrotron radiation X-ray diffraction

Abstract We investigated the temperature-dependent crystal structure of a BaTiO3−KNbO3 (BT−KN) nanocomposite particle in which the KN shell epitaxially covers the BT core. Synchrotron radiation X-ray diffraction experiments were performed over a temperature range of 300–800 K. Near the interface, BT and KN were found to be bonded in a pseudo-cubic crystal structure with similar lattice constants across all temperatures. As the temperature decreased, strain-gradient regions (SGRs) near the interface, caused by lattice mismatch, enlarged significantly owing to phase transitions. The largest SGRs with a tetragonal BT core and an orthorhombic KN shell were observed at 300 K. However, SGRs were minimal at 800 K, where both BT and KN possessed cubic crystal structures. Engineering interfaces such as SGRs can enhance the dielectric constant; therefore, it is crucial to consider material combinations with different crystal symmetries but similar unit cell volumes, such as BT−KN at RT.

Fracture-induced broken inversion symmetry and crack healing in organic crystals

Fracture-induced broken inversion symmetry and crack healing in organic crystals

Reduced crystal symmetry as the origin of the ferroelectric polarization within the commensurate magnetic phase of TbMn2O5

Reduced crystal symmetry as the origin of the ferroelectric polarization within the commensurate magnetic phase of TbMn₂O₅

Piezoelectric altermagnetism and spin-valley polarization in Janus monolayer Cr2SO

Altermagnetism can achieve spin-split bands in collinear symmetry-compensated antiferromagnets. Here, we predict altermagnetic order in Janus monolayer Cr2SO with eliminated inversion symmetry, which can realize the combination of piezoelectricity and altermagnetism in a two-dimensional (2D) material, namely, 2D piezoelectric altermagnetism. It is found that Cr2SO is an altermagnetic semiconductor, and the spin-split bands of both valence and conduction bands are near the Fermi level. The Cr2SO has large out-of-plane piezoelectricity (|d31| = 0.97 pm/V), which is highly desirable for ultrathin piezoelectric device application. Due to spin-valley locking, both spin and valley can be polarized by simply breaking the corresponding crystal symmetry with uniaxial strain. Our findings provide a platform to integrate spin, piezoelectricity, and valley in a single material, which is useful for multi-functional device applications.

Large Phase-Transition Temperature Enhancement Achieved in a Layered Lead Iodide Hybrid Crystal by H/F Substitution.

Organic-inorganic hybrid metal halides with structural flexibility and solution processability have been widely investigated for different application scenarios. However, the effective construction of phase-transition materials with a high phase-transition temperature (Ttr) for potential practical applications remains a great challenge, and reports on the regulation of Ttr with significant enhancement have been rare. In this manuscript, we have realized a large Ttr increase of 148 K in a layered hybrid lead iodide crystal (4-FTMBA)4Pb3I10 (4-FTMBA = 4-fluoro-N,N,N-trimethylbenzenaminium) by the H/F substitution strategy. Compared to the parent (TMBA)4Pb3I10 (TMBA = N,N,N-trimethylbenzenaminium), H/F substitution preserves the structural framework and crystal symmetry in (4-FTMBA)4Pb3I10. The introduction of heavier fluorine will significantly increase the motion barrier for the order-disorder transition, resulting in the remarkably improved Ttr. Temperature-dependent crystal structures, Raman spectra, and dielectric analyses well support the phase-transition behavior. In addition, evident thermochromism with a tunable direct band gap in (4-FTMBA)4Pb3I10 has been observed using UV-vis spectra. To the best of our knowledge, the achieved Ttr enhancement of 148 K by H/F substitution is the highest among the organic-inorganic hybrid lead halide phase-transition materials. This finding would greatly inspire the rational design of functional materials with high performance.

Study of the synergistic role of multivalence states of 3d cations on the crystal lattice distortion and magnetic behavior of Sr2FeCoO6-δ: A spectroscopic study

In perovskite oxides, the multiple charge states of cations influence their local structure and correlated physical properties. In this report, we studied the role of multivalence cations on the local structure and magnetic behavior of the oxygen-deficient system Sr2FeCoO6-δ (SFCO), prepared by the solid-state synthesis technique. A detailed structural and geometrical analysis confirmed the coexistence of orthorhombic (Brownmillerite) and cubic crystal symmetries and a gesture of the Jahn-Teller (JT) distortion. The intense Raman modes are allowed to be indexed for BO-polyhedra and JT-distortion. Experimental and theoretical analysis of the X-ray photoelectron spectroscopy (XPS) spectra supported the mixed oxidation state of Fe (Fe3+/Fe4+) and Co (Co2+/Co3+), further confirmed by theoretically simulated X-ray absorption spectroscopy (XAS) spectra. The presence of the multivalence states leads to AFM/FM exchange interaction in the sample which further leads to glassy magnetic behavior.

Magnetic Field-Induced Spin Nematic Phase Up to Room Temperature in Epitaxial Antiferromagnetic FeTe Thin Films Grown by Molecular Beam Epitaxy.

Electronic nematicity, where strong correlations drive electrons to align in a way that lowers the crystal symmetry, is ubiquitous among unconventional superconductors. Understanding the interplay of such a nematic state with other electronic phases underpins the complex behavior of these materials and the potential for tuning their properties through external stimuli. Here, we report magnetic field-induced spin nematicity in a model system tetragonal FeTe, the parent compound of iron chalcogenide superconductors, which exhibits a bicollinear antiferromagnetic order. The studies were conducted on epitaxial FeTe thin films grown on SrTiO3(001) substrates by molecular beam epitaxy, where the bicollinear antiferromagnetic order was confirmed by in situ atomic resolution scanning tunneling microscopy imaging. A 2-fold anisotropy is observed in in-plane angle-dependent magnetoresistance measurements, indicative of magnetic field-induced nematicity. Such 2-fold anisotropy persists up to 300 K, well-above the bicollinear antiferromagnetic ordering temperature of 75 K, indicating a magnetic field-induced spin nematic phase up to room temperature in the antiferromagnet FeTe.

Crystal Structure, Magnetic, and Dielectric Properties of (x)CoFe2O4–(1−x)Ba0.8Sr0.2TiO3 Multiferroics

The composites (x)CoFe2O4–(1−x)Ba0.8Sr0.2TiO3 are prepared by solid‐state reaction method using microwave double‐step sintering. Ba0.8Sr0.2TiO3 crystallizes to tetragonal crystal symmetry with P4mm space group and CoFe2O4 crystallizes to cubic crystal symmetry with space group. Electron microscopy techniques are used to understand the microstructure, elemental composition, and morphology of the composites. The dielectric properties are measured in the 1 Hz–1 MHz frequency range and 40–400 °C temperature range. Composite with x = 0.1 (ε′ ≈ 170, tan δ = 0.08 at 1 kHz) and 0.2 (ε′ ≈ 390, tan δ = 0.07 at 1 kHz) has better dielectric properties than the parent Ba0.8Sr0.2TiO3 ferroelectric (ε′ ≈ 125, tan δ = 0.16 at 1 kHz) and CoFe2O4 ferrimagnetic phases (ε′ ≈ 375, tan δ = 0.72 at 1 kHz), respectively. Composite with 10% cobalt ferrite has the highest saturation polarization (2.1 μC cm−2), the highest remanent polarization (0.9 μC cm−2), and coercive field (23.9 kV cm−1) compared to ferroelectric phase followed by x = 0.2 composite (PS = 1.6 μC cm−2, Pr = 0.8 μC cm−2, and EC = 19.2 kV cm−1). Composite with x = 0.2 shows the highest magnetic coercive field of 1.96 kOe. Hence, this article advocates that 20% ferrite in the composites is the optimized composition for multiferroic applications. The present study will help to explore piezoelectric, magnetostrictive, and magnetoelectric properties of (x)CoFe2O4–(1−x)Ba0.8Sr0.2TiO3 for the technological application.

Revealing the Hidden Spin-Polarized Bands in a Superconducting Tl Bilayer Crystal.

The interplay of spin-orbit coupling and crystal symmetry can generate spin-polarized bands in materials only a few atomic layers thick, potentially leading to unprecedented physical properties. In the case of bilayer materials with global inversion symmetry, locally broken inversion symmetry can generate degenerate spin-polarized bands, in which the spins in each layer are oppositely polarized. Here, we demonstrate that the hidden spins in a Tl bilayer crystal are revealed by growing it on Ag(111) of sizable lattice mismatch, together with the appearance of a remarkable phenomenon unique to centrosymmetric hidden-spin bilayer crystals: a novel band splitting in both spin and space. The key to success in observing this novel splitting is that the interaction at the interface has just the right strength: it does not destroy the original wave functions of the Tl bilayer but is strong enough to induce an energy separation.

Crystal structure engineering of GdFeO3/Mxene composites with excellent electromagnetic wave absorption: Role of phase transition and high polarizability

The development of new materials capable of absorbing electromagnetic waves (EMA) is crucial to address issues like signal interference and crosstalk. In this study, we synthesized a novel composite material by combining MXene with GdFeO3 nanoparticles, employing crystal structure engineering to enhance electromagnetic wave attenuation between 2 and 18 GHz. The GdFeO3 (GFO) nanoparticles, sized at 30–40 nm, were evenly dispersed on the MXene layers' surface. Analysis of the composite material through XRD and Raman spectra revealed different phases of GdFeO3, exhibiting distinct crystal symmetries and coordination states. XPS and EPR measurements indicated the coexistence of various valence states of Fe, leading to oxygen vacancies within the lattice. By incorporating MXene, the composite material's specific surface area, and dielectric properties were significantly increased. The improved polarization and phase transition behavior resulted in a remarkable enhancement of the P-E loop, DM constant, and attenuation constant. The combination of the high-quality ferroelectric GdFeO3 and the disordered crystal phase within the multilayered MXene matrix led to enhanced conductive and magnetic losses. Experimental results demonstrated that the Pbnm GdFeO3/MXene composites displayed outstanding EMA performance. At a 4 mm thickness, the minimum reflection loss achieved was − 61.5 dB, and an impressive effective absorption bandwidth of 8.62 GHz was attained at 10.8 GHz. This achievement can be attributed to the exceptional dielectric, magnetic, and multiple reflections contributing to the superior EMA absorption performance, providing a broad band of frequencies.

An optimized growth model for Fe/Pt heteroepitaxy by computational and structural studies

Thin layers of ferromagnetic/non-magnetic bimetallic heterostructures have become the focal point of spintronics, primarily due to their capacity to convert spin to charge current, leveraging the spin- and inverse spin Hall effects. However, the interfacial properties and morphologies can significantly influence this conversion. Hence, we employed molecular dynamics calculations to model the construction of the Fe/Pt interface at various bilayer growth temperatures and Pt deposition rates. We then experimentally evaluated the modeling using x-ray methods to resolve the chemical and structural state of the interface. The calculations revealed moderate diffusive phenomena between the adjacent layers and an interfacial roughness of less than 1 nm, consistent with the experimental observations. In cases where plastic relaxation of the Fe/Pt interface is insufficient, lattice deformation is mitigated by a local pseudomorphic growth caused by transformation of the Pt crystal symmetry. Additionally, interfacial planar defects may emerge as a complementary stress-relieving mechanism to misfit dislocations. By combining the experimental and computational findings, we propose optimized growth conditions for an “ideal” Fe/Pt interface, which could serve as a useful tool to control the efficiency of spin-to-charge conversion.

Magnetically Triggered Interplay of Capacitive and Diffusion Contributions for Boosted Supercapacitor Performance.

The chemistry involved in supercapacitors in terms of their mechanistic contributions leading to improved specific capacity will aid in easy commercialization. The main contributory factors in a supercapacitor are either capacitive (non-diffusion controlled) or ion-diffusion behavior, which results in enhanced charge-discharge characteristics of a supercapacitor reflected in its power density, whereas ion-diffusion behavior will lead to the enhanced energy density of a supercapacitor. In this context, the present article attempts to understand the use of external magnetic fields, leading to the interplay between capacitive and ion-diffusion behavior in a high-performance supercapacitor. The model system chosen in the present study, nickel cobalt copper carbonate hydroxide (NiCoCuCH), can effectively address the interplay between capacitive and ion diffusion contributions by varying total magnetic effects involving magnetic dilution. The magneto-enhancement of the electrodes nickel cobalt copper carbonate hydroxide (NiCoCuCH) and aluminum-doped nickel cobalt copper carbonate hydroxide (Al-NiCoCuCH) was demonstrated under the magnetic field from 0 to 250 mT. Both NiCoCuCH and Al-NiCoCuCH show dominant non-diffusion-controlled (capacitive) and diffusion-controlled behavior as a function of the applied external magnetic field. Under the influence of the external magnetic field, ferromagnetic coupling between metal-oxygen-metal centers via oxygen 2p orbitals enhances, leading to a facile redox pathway. To further control the charge-discharge behavior of the electrode via the interplay between diffusive and capacitive, a non-magnetic ion, Al3+, was doped into the bare metal carbonate hydroxide crystal lattice. The Al3+ ion not only alters the crystal symmetry but also restricts the alignment of the magnetic domains in the electrode, leading to a sluggish redox pathway, effectively increasing the capacitive contribution, and leading to improved charge-discharge characteristics at the expense of energy density. We have constructed an asymmetric device with the best-performing (110 mT) NiCoCuCH electrode as a positive electrode and activated carbon as a negative electrode. The NiCoCuCH/AC ASC device at 110 mT has the largest specific capacity (1100 C g-1 at 2 A g-1) at 110 mT, leading to a high energy density (250 W h kg-1) and a power density (1.7 kW kg-1) of the electrode.

Engineering of brick and staple components for ordered assembly of synthetic repeat proteins

Synthetic ɑRep repeat proteins are engineered as Brick and Staple protein pairs that together self-assemble into helical filaments. In most cases, the filaments spontaneously form supercrystals. Here, we describe an expanded series of ɑRep Bricks designed to stabilize the interaction between consecutive Bricks, to control the length of the assembled multimers, or to alter the spatial distribution of the Staple on the filaments. The effects of these Brick modifications on the assembly, on the final filament structure and on the crystal symmetry are analyzed by biochemical methods, electron microscopy and small angle X-ray scattering. We further extend the concept of Brick/Staple protein origami by designing a new type of “Janus”-like Brick protein that is equally assembled by orthogonal staples binding its inner or outer surfaces and thus ending inside or outside the filaments. The relative roles of longitudinal and lateral associations in the assembly process are discussed. This set of results demonstrates important proofs-of-principle for engineering these remarkably versatile proteins toward nanometer-to-micron scale constructions.

Synergistic red dominancy over green upconversion studies in PbZrTiO3: Er3+/Yb3+ phosphor synthesized via two different modified technique and flexible thin-film thermometer demonstration on C1: PbZrTiO3 @PDMS substrates

Owing to its efficient wide range sensing using a noncontact mechanism with a decimal accuracy level, quick, non-invasive temperature sensors utilizing upconversion (UC) phosphor were examined. These sensors are perfect for cutting-edge applications such as measuring the intracellular temperature and identifying microelectronic issues. It may be possible to modify the performance of phosphor temperature sensors through nanoscale engineering. Despite were potential, it has been discovered that modern nanothermometers are ineffective in maintaining stability over a wide temperature range. Motivated by previous studies on efficient UC based solar cell demonstrations of Er3+/Yb3+: PbZrTiO3 (lead zirconate titanate) phosphors, the UC properties of Er3+/Yb3+: PbZrTiO3 for a wide range of temperature sensing and practical thermometer applications have been investigated. The UC emission properties of the Er3+/Yb3+: PbZrTiO3 phosphors synthesized via different routes, with the same dopant concentration, were compared. We have also investigated the formation of two different crystal symmetry, and an approach for the fine-tuning of the emission from the green to the red region upon changing the synthesis technique. The strategy of choosing an optimized synthesis route, based upon structural investigations, could be a way forward where dopant modification in phosphors is ruled out. Based on the UC optimization, the green and red dominant phosphors under 980 nm excitation with different pulse widths and power densities or at different temperatures were studied; the possible mechanisms were discussed in detail. The sensitivity of Er3+/Yb3+: PbZrTiO3 was independent of the pumping laser characteristics since it was essentially consistent when utilising both continuous wave and laser pulse width modulation or varying power densities. To assess the temperature of the microelectronic components, a flexible thin-film thermometer was made of Er3+/Yb3+: PbZrTiO3 on a polyDiMethylSiloxane substrate. This thermometer shows great repeatability and can measure the temperature of an electronic circuit board correctly. The findings suggested that the current non-contact UC temperature sensor might potentially replace conventional thermometers because of its steady green emission over a wide temperature range (313–673 K) and thermometric sensitivity.

Structure and Relaxor Behavior of (0.5 − x)BiFeO3-0.5PbFe0.5Nb0.5O3-xPbTiO3 Ternary Ceramics

Ceramics of the quasi-binary concentration section (0.1 ≤ x ≤ 0.2, Δx = 0.025) of the ternary solid solution system (0.5 − x)BiFeO3-0.5PbFe0.5Nb0.5O3-xPbTiO3 were prepared by the conventional solid-phase reaction method. An X-ray study at different temperatures revealed that (0.5 − x)BF-0.5PFN-xPT ceramics have a cluster morphology. Clusters have different modulation, crystal lattice symmetry, and chemical composition. The presence of a cluster structure in a solid solution with heterovalent substitution, consisting of regions rich in Ti+4, Nb+5, or Fe3+, has led to the appearance of Maxwell–Wagner polarization in the studied ceramics. The study of the dielectric characteristics revealed the relaxor-like behavior of the studied ceramics. The grain morphology, dielectric, pyroelectric, and piezoelectric properties of the selected solid solutions were investigated. The highest piezoelectric coefficient, d33 = 280 pC/N, was obtained in the 0.3BiFeO3-0.5PbFe0.5Nb0.5O3-0.2PbTiO3 ceramics. Study of the dielectric characteristics of all samples revealed relaxor ferroelectric behavior and a region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 140–170 °C.

Accurate, interpretable predictions of materials properties within transformer language models

Property prediction accuracy has long been a key parameter of machine learning in materials informatics. Accordingly, advanced models showing state-of-the-art performance turn into highly parameterized black boxes missing interpretability. Here, we present an elegant way to make their reasoning transparent. Human-readable text-based descriptions automatically generated within a suite of open-source tools are proposed as materials representation. Transformer language models pretrained on 2 million peer-reviewed articles take as input well-known terms such as chemical composition, crystal symmetry, and site geometry. Our approach outperforms crystal graph networks by classifying four out of five analyzed properties if one considers all available reference data. Moreover, fine-tuned text-based models show high accuracy in the ultra-small data limit. Explanations of their internal machinery are produced using local interpretability techniques and are faithful and consistent with domain expert rationales. This language-centric framework makes accurate property predictions accessible to people without artificial-intelligence expertise.

Magnetic phase transition and variation in physical properties of Mn2MnB′O6 (B′ = Mo, Sb) via strain engineering

The influence of uniaxial strain on structure, magnetic, electronic, elastic, ferroelectric and piezoelectric properties of corundum double oxides Mn2MnB'O6 (B′ = Mo, Sb) is investigated using first principle calculations. These compounds have six independent sites occupied by Mn1, Mn2, Mn3, Mo/Sb, O1 and O2 ions. Ferrimagnetic (FiM) is the favorable ground state magnetic phase due to difference in magnetic moments of cation face sharing octahedra. The strain confined the magnetic orbital and led to reduced the strength of AFM coupling, which results in magnetic phase transition from FiM to ferromagnetic. These compounds are found semiconductors with band gap values 1.18 and 0.63 eV for Mn2MnMoO6 and Mn2MnSbO6 respectively. The narrowness and wideness in the band gap is observed with tensile and compressive strain respectively. The strain-free elastic constants revealed that these compounds are stable in rhombohedral crystal symmetry, linearly decrease occurred in elastic constants, with compressive to tensile strain. The calculated high values of spontaneous polarization 63.28 and 31.64 μC/cm2 make these materials suitable candidates for ferroelectric application. Polarization in these compounds is reversible with strain. The larger values of piezoelectric coefficient reveal that these compounds are good lead-free piezoelectric materials.

Determination of effective properties of porous piezoelectric composite with partially randomly metalized pore boundaries using finite element method

In this study, we investigate the effective characteristics of a porous piezocomposite with randomly distributed pores of arbitrary size and with partly metalized pore boundaries. Using the ANSYS APDL finite element software, we created a novel random representative volume element (RVE), applied the finite element approach to solve boundary value problems of homogenization, and calculated equivalent properties using the Hill–Mandel principle. The results demonstrate that when large random RVE and an appropriate finite element mesh are used, the porous piezocomposite with randomly metalized porosity borders will have the same crystal symmetry as the piezoceramic matrix. Therefore, when there is a significant material contrast between the various phases, a large random RVE is preferred in the modeling of particulate-filled composites. Furthermore, when the areas of metalized surfaces increase, the performance of the investigated composite in transverse sensing and actuation applications improves.

Localised surface plasmon resonance inducing cooperative Jahn–Teller effect for crystal phase-change in a nanocrystal

The Jahn–Teller effect, a phase transition phenomenon involving the spontaneous breakdown of symmetry in molecules and crystals, causes important physical and chemical changes that affect various fields of science. In this study, we discovered that localised surface plasmon resonance (LSPR) induced the cooperative Jahn–Teller effect in covellite CuS nanocrystals (NCs), causing metastable displacive ion movements. Electron diffraction measurements under photo illumination, ultrafast time-resolved electron diffraction analyses, and theoretical calculations of semiconductive plasmonic CuS NCs showed that metastable displacive ion movements due to the LSPR-induced cooperative Jahn–Teller effect delayed the relaxation of LSPR in the microsecond region. Furthermore, the displacive ion movements caused photo-switching of the conductivity in CuS NC films at room temperature (22 °C), such as in transparent variable resistance infrared sensors. This study pushes the limits of plasmonics from tentative control of collective oscillation to metastable crystal structure manipulation.

Enhancing upconversion of Sc2Mo3O12:Yb/Ln (Ln = Er, Ho) phosphors by doping Ca2+ ions

Lanthanide doped Sc2(MoO4)3 upconversion (UC) crystals showed distinct negative thermal quenching effect, which show promising applications in the temperature sensing field. However, it is still valuable to develop novel routes to enhance the room temperature UC intensity. Herein, the UC intensity of the Yb/Er (Ho) doped Sc2Mo3O12 crystals were significantly enhanced by doping Ca2+ ions. The incorporation of Ca2+ ions can break the crystal symmetry around the activators and then promote the 4f-4f transitions followed by the enhanced UC. Especially, the UC intensity of the Sc2Mo3O12:20Yb/1Ho/20Ca was about 100 times than that of Sc2Mo3O12:20Yb/1Ho phosphors. Furthermore, the thermally couple levels based temperature sensing performance was improved after doping Ca2+ ions. Our results may promote the exploration of novel scheelite structural compounds with superior UC properties.