Atomic Displacements Research Articles

Lattice dynamics and Raman spectrum of supertetragonal PbVO3

Lead vanadate PbVO3 is a polar crystal with a P4mm space group under ambient conditions. PbVO3 is isostructural with the model soft mode-driven ferroelectric PbTiO3, but it differs due to the so-called “supertetragonal” elongation of its unit cell. In this study, we investigated the lattice dynamics of PbVO3 based on Raman spectroscopy at room temperature and first-principle calculations. All zone-center transverse optical phonon modes were identified by polarized, angle-dependent Raman spectroscopy and assigned as follows: E modes at 136, 269, 374, and 508 cm−1; A1 modes at 188, 429, and 874 cm−1, and B1 mode at 319 cm−1. The calculations confirmed the experimental symmetry assignment and allowed us to obtain the longitudinal optical phonon wavenumbers. In addition, we analyzed the mode eigenvectors in detail in order to identify the atomic displacements associated with each mode and compare them with PbTiO3. Despite differences in chemistry and strain, the phonon eigenvectors were found to be highly comparable in both compounds. We investigated the position of the ferroelectric soft mode in PbVO3 compared with PbTiO3. Sizeable splitting of the B1+E modes appeared as a characteristic feature of supertetragonal phases. The peculiarity of the vanadyl V–O bond frequency in PbVO3 was also addressed.

A Density-Functional Theory Study of Hole and Defect-Bound Exciton Polarons in Lithium Niobate

Hole polarons and defect-bound exciton polarons in lithium niobate are investigated by means of density-functional theory, where the localization of the holes is achieved by applying the +U approach to the oxygen 2p orbitals. We find three principal configurations of hole polarons: (i) self-trapped holes localized at displaced regular oxygen atoms and (ii) two other configurations bound to a lithium vacancy either at a threefold coordinated oxygen atom above or at a two-fold coordinated oxygen atom below the defect. The latter is the most stable and is in excellent quantitative agreement with measured g factors from electron paramagnetic resonance. Due to the absence of mid-gap states, none of these hole polarons can explain the broad optical absorption centered between 2.5 and 2.8 eV that is observed in transient absorption spectroscopy, but such states appear if a free electron polaron is trapped at the same lithium vacancy as the bound hole polaron, resulting in an exciton polaron. The dielectric function calculated by solving the Bethe–Salpeter equation indeed yields an optical peak at 2.6 eV in agreement with the two-photon experiments. The coexistence of hole and exciton polarons, which are simultaneously created in optical excitations, thus satisfactorily explains the reported experimental data.

An optimization study for targeted alpha therapy: Ion behaviours and dose calculations within ICRU-compact bone tissue

Targeted Alpha Therapy is a therapy method that can be applied to late-stage cancers, including bone metastases, and it is a hope for millions of people. This study is an optimization that includes the interactions of bone tissue with characteristic alpha particles of 223Ra, 225Ac (together with their decay product), which are frequently preferred in Targeted Alpha Therapy that aim to destroy metastatic tumour tissue in bone tissue. This optimization is designed to analyse some events such as ion spacing of alpha particles that can only infiltrate into bone tissue, stopping power of the target, dose calculations and atomic displacement. To ensure accuracy, calculations such as mass stopping power and ionizing dose obtained from CASP, SRIM and ASTAR programs were also compared among themselves. And then, tissue doses were calculated in IDAC-Dose 2.1, taking into account the half-lives of the radioisotopes, the administered activity and the integration time. Alpha particles of 213Po had the highest ion spacing, while alpha particles of 223Ra had the lowest ion range.

Parameters of cascade mixing for FeCr alloy: Results of atomistic simulation

By means of molecular dynamics simulation, the parameters of atomic replacements in displacement cascades (cascade mixing) have been obtained for Fe-9%Cr and Cr-10%Fe alloys and in pure α-Fe. We have considered the threshold energy of atomic replacement and modified a function recently proposed in the literature for calculating the number of atomic replacements in a cascade. The parameters of atomic displacements and replacements have been evaluated for several neutron spectra of fission reactors and the future DEMO fusion reactor. These parameters are intended for use in models of radiation-accelerated precipitation of chromium in FeCr alloys under irradiation, which take into account the flux effect.

Experimental X-ray Charge-Density Studies─A Suitable Probe for Superconductivity? A Case Study on MgB2.

Case studies of 1T-TiSe2 and YBa2Cu3O7-δ have demonstrated that X-ray diffraction (XRD) studies can be used to trace even subtle structural phase transitions which are inherently connected with the onset of superconductivity in these benchmark systems. However, the utility of XRD in the investigation of superconductors like MgB2 lacking an additional symmetry-breaking structural phase transition is not immediately evident. Nevertheless, high-resolution powder XRD experiments on MgB2 in combination with maximum entropy method analyses hinted at differences between the electron density distributions at room temperature and 15 K, that is, below the Tc of approx. 39 K. The high-resolution single-crystal XRD experiments in combination with multipolar refinements presented here can reproduce these results but show that the observed temperature-dependent density changes are almost entirely due to a decrease of atomic displacement parameters as a natural consequence of a reduced thermal vibration amplitude with decreasing temperature. Our investigations also shed new light on the presence or absence of magnesium vacancies in MgB2 samples─a defect type claimed to control the superconducting properties of the compound. We propose that previous reports on the tendency of MgB2 to form non-stoichiometric Mg1-xB2 phases (1 - x ∼ 0.95) during high-temperature (HT) synthesis might result from the interpretation of XRD data of insufficient resolution and/or usage of inflexible refinement models. Indeed, advanced refinements based on an Extended Hansen-Coppens multipolar model and high-resolution X-ray data, which consider explicitly the contraction of core and valence shells of the magnesium cations, do not provide any significant evidence for the formation of non-stoichiometric Mg1-xB2 phases during HT synthesis.

Micro-mechanical properties of foamed polymer rehabilitation material: A molecular dynamics study

The non-aqueous reactive foamed polyurethane is widely used in engineering. We have observed the micromorphology of the non-aqueous reactive foamed polyurethane by field emission scanning electron microscope. It is found that the pores are closed and the minimum pore wall thickness is only 63.5 nm. Therefore, we proposed a method to construct a microscopic model of the polyurethane closed pores with different densities. Combined with the change of non-affine displacement of atoms in the process of compression deformation, the influence mechanism of density and strain rate on the mechanical properties of polyurethane closed pores is studied from the microscopic scale, and compared with that of polyurethane elastomers. The results show that the yield strength of polyurethane closed pores increases with the increase of strain rate and density, and the yield strain of the pores is almost not affected by the density, but will increase with the increase of strain rate. The smaller the density, the greater the effect of strain rate on the polyurethane closed pores which is consistent with the experimental results. The polyurethane closed pores and elastomers will yield when the atoms whose non-affine displacement exceeds 1 Å accumulate to a certain extent. The increase of strain rate will make the number of atoms with non-affine displacement exceeding 1 Å less, so the pores will yield at higher strain. Under the same conditions, the yield stress and yield strain of polyurethane elastomers are significantly greater than that of polyurethane closed pores, and the average non-affine displacement of atoms in the pores is significantly greater than that of atoms in polyurethane elastomers, which indicates that more severe cavitation and chain slip phenomena will occur in the pores. The simulation results of this paper analyzed the mechanical properties of foamed polyurethane from a new perspective.

Comment on "Manifolds of quasi-constant SOAP and ACSF fingerprints and the resulting failure to machine learn four-body interactions" [J. Chem. Phys. 156, 034302 (2022)

The "quasi-constant" smooth overlap of atomic position and atom-centered symmetry function fingerprint manifolds recently discovered by Parsaeifard and Goedecker [J. Chem. Phys. 156, 034302 (2022)] are closely related to the degenerate pairs of configurations, which are known shortcomings of all low-body-order atom-density correlation representations of molecular structures. Configurations that are rigorously singular-which we demonstrate can only occur in finite, discrete sets and not as a continuous manifold-determine the complete failure of machine-learning models built on this class of descriptors. The "quasi-constant" manifolds, on the other hand, exhibit low but non-zero sensitivity to atomic displacements. As a consequence, for any such manifold, it is possible to optimize model parameters and the training set to mitigate their impact on learning even though this is often impractical and it is preferable to use descriptors that avoid both exact singularities and the associated numerical instability.

Atomic mechanisms of self-diffusion in amorphous silicon

Based on recent calculations of the self-diffusion (SD) coefficient in amorphous silicon (a-Si) by classical Molecular Dynamics simulation [Posselt et al., J. Appl. Phys. 131, 035102 (2022)], detailed investigations on atomic mechanisms are performed. For this purpose, two Stillinger–Weber-type potentials are used, one strongly overestimates the SD coefficient, while the other leads to values much closer to the experimental data. By taking into account the individual squared displacements (or diffusion lengths) of atoms, the diffusional and vibrational contributions to the total mean squared displacement can be determined separately. It is shown that the diffusional part is not directly correlated with the concentration of coordination defects. The time-dependent distribution of squared displacements of atoms indicates that in a-Si, a well-defined elemental diffusion length does not exist, in contrast to SD in the crystalline Si. The analysis of atoms with large squared displacements reveals that the mechanisms of SD in a-Si are characterized by complex rearrangements of bonds or exchanges of neighbors. These are mono- and bi-directional exchanges of neighbors and neighbor replacements. Exchanges or replacements may concern up to three neighbors and may occur in relatively short periods of some ps. Bi- or mono-directional exchange or replacement of one neighbor atom happens more frequently than processes including more neighbors. A comparison of results for the two interatomic potentials shows that an increased three-body parameter only slows down the migration but does not change the migration mechanisms fundamentally.

Accurate quantification of lattice temperature dynamics from ultrafast electron diffraction of single-crystal films using dynamical scattering simulations.

In ultrafast electron diffraction (UED) experiments, accurate retrieval of time-resolved structural parameters, such as atomic coordinates and thermal displacement parameters, requires an accurate scattering model. Unfortunately, kinematical models are often inaccurate even for relativistic electron probes, especially for dense, oriented single crystals where strong channeling and multiple scattering effects are present. This article introduces and demonstrates dynamical scattering models tailored for quantitative analysis of UED experiments performed on single-crystal films. As a case study, we examine ultrafast laser heating of single-crystal gold films. Comparison of kinematical and dynamical models reveals the strong effects of dynamical scattering within nm-scale films and their dependence on sample topography and probe kinetic energy. Applying to UED experiments on an 11 nm thick film using 750 keV electron probe pulses, the dynamical models provide a tenfold improvement over a comparable kinematical model in matching the measured UED patterns. Also, the retrieved lattice temperature rise is in very good agreement with predictions based on previously measured optical constants of gold, whereas fitting the Debye-Waller factor retrieves values that are more than three times lower. Altogether, these results show the importance of a dynamical scattering theory for quantitative analysis of UED and demonstrate models that can be practically applied to single-crystal materials and heterostructures.

Recoil and charged particle energy spectra from the natSi(n,x) reaction and the Si semiconductor detector response to the 14 MeV neutrons

The energy spectra of light and heavy charged particles generated by the 14 MeV neutrons in silicon nuclei and in the Si semiconductor detector (SSD) were analysed. The existing measurements were used to validate the corresponding energy differential cross sections from major evaluations ENDF/B-VIII.0 and JEFF-3.3. The required data were extracted by the various codes: NJOY21, SPKA and MCNP6. It was shown that both evaluations underestimate the high energy part of the 28Si(n,x)p- and α-particle spectra by ≤50%, whereas at smaller emission energies no experimental data even exist. The calculation of the atom displacement damage in SSD reveals that the secondary protons produce additionally ≈15% of damage, whereas the contribution from secondary alphas is impossible to estimate since the Si(α,x) recoil data are not available.The single experiment, carried out by K. Yageta and co-workers in 1988, reported the energy spectra in the Si semiconductor down to the rather low energy of ≈0.3 MeV, at which the production of reaction recoils dominates over the light ions. The Monte Carlo simulation of this experiment was performed by MCNP6. The generation and transport of all relevant ions were taken in account. The energy depositions from protons or alphas were summed with their associated recoils after correction for non-ionization losses. The neutron reactions in the dead layer of the SSD were shown to increase the counts in active layer by (1–20)% depending on sort of ions. The impact of the field funneling effect was studied. Consideration of all these underlying processes has eventually allowed a reasonable reproduction of this experiment.

Neutronic and Shielding Analyses for the DTT Electronics

The radiation effect on electronic devices is a critical issue for nuclear facilities, accelerators, and spatial missions as well as for fusion machines. Phenomena related to particle interactions have significant impact on the normal functioning of such devices: they could arise progressively during machine lifetime due to the cumulated ionization [total ionizing dose (TID)], cumulated atomic displacement (dpa) or it can appear instantaneously after a single highly ionizing particle interaction [single-event effect (SEE)]. The divertor tokamak test (DTT) facility is a tokamak machine, which will produce, in its high-performance phase, up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\times 1017$ </tex-math></inline-formula> n/s at 2.45 MeV from deuterium–deuterium reactions plus about 1% of 14.1-MeV neutrons produced by the triton burn-up inside the plasma. Such significant neutron production implies a severe radiation environment, up to 1010 n/cm2/s and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times 109\,\,\gamma $ </tex-math></inline-formula> /cm2/s [secondary gammas mainly due to (n, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> ) reactions], inside Torus Hall building (THB) and outside the THB nearby the penetrations. DTT will be equipped with several power and signal electronic devices: 1) critical electronics that play a crucial role for the machine functioning in order to avoid failure, loss of plasma stability, and damages on the structural components (e.g., energy supply to the toroidal field, poloidal field, and central solenoid superconductive magnets); and 2) noncritical electronics, used to power diagnostics and systems whose failures do not compromise the machine operations, but are essential for scientific and engineering exploitation programs. Neutronics and shielding studies of electronics are fundamental for protecting the main components of the tokamak and to avoid the failure of the critical systems, as well as for the evaluation of the positioning and functioning of the noncritical devices and the selection of radiation-hard electronics. In this work, 3-D shielding studies for the DTT electronics devices, carried out with MCNP Monte Carlo code, are presented and discussed as well as the effectiveness of the proposed arrangement and mitigation solutions.

On the frontiers of coupled extreme environments

Coupled extreme environments pose among the highest demands on materials, stressing the limits of temperature, pressure, electric and magnetic fields, atomic displacement rates, and chemical potentials that can be simultaneously sustained. This issue highlights exciting new materials science methods that will enable rapid progress in what has traditionally been the most difficult materials arena. New opportunities in artificial intelligence, multi-physics simulations capabilities, the use of extreme conditions to synthesize novel materials, and our ability to interrogate materials under relevant conditions provide new avenues to understand and design new materials. Graphical abstract

Deformation twinning in octahedron-based face-centered cubic metallic structures: Localized shear-force dipoles drive atomic displacements

• Monocrystalline (Fe, Nb) 23 Zr 6 nanoparticles (NPs) with an octahedron-motif-based Mn 23 Th 6 -type FCC structure were found to precipitate in a Zr-Nb-Fe alloy. • Deformation twinning was successfully introduced in the (Fe, Nb) 23 Zr 6 NPs by cold work on the Zr-Nb-Fe alloy. • The processing deformation twinning states were observed by high-resolution transmission electron microscopy (HRTEM) assisted by geometric phase analysis (GPA). • A new zero-net-strain path for the <112>{111} deformation twinning in FCC structures was discovered. • A loading criterion for deformation twinning of a FCC NP under uniaxial compression is proposed. Twinning is found to impart favorable mechanical, physical and chemical properties to nanostructured materials. Deformation twinning prevails in face-centered cubic (FCC) nanocrystalline materials upon loading. In FCC structures, the <112>{111} deformation twinning is traditionally believed to nucleate and grow through layer-by-layer emission of 1/6<112> Shockley partial dislocations on consecutive {111} planes. We report that deformation twinning is able to occur in crystalline (Fe, Nb) 23 Zr 6 nanoparticles (NPs) that have a large Mn 23 Th 6 -type FCC structure with a Zr-octahedron as a motif. Based on direct atomic-scale observations, we discover a new zero-net-strain path for the <112>{111} deformation twinning in FCC structures. To form a [ 1 ¯ 1 ¯ 2]/(111) twin, for example, short ( 1 ¯ 1 ¯ 1) planes within two adjacent (111) plane layers in the repeated three-layer sequence of (111) planes are shear deformed continuously by a shear-force dipole along the [11 2 ¯ ] direction like a domino effect, whereas the other (111) plane in the repeated sequence remains intact. In addition, a loading criterion for deformation twinning of a FCC NP under uniaxial compression is proposed based on our observations. Our work here not only extends the fundamental understanding on deformation twinning in FCC structures, but also opens up studies of deformation behaviors in a class of Mn 23 Th 6 -type FCC materials.

Dynamic lattice distortion in metallic nanocrystals

Advanced design of metallic nanocrystals (NCs) for plasmonic applications requires control of the dynamic lattice distortion. Here we apply atomistic simulations coupled with total scattering to study the lattice vibrations induced by the thermal motion of atoms in Pd NCs. Quantitative analysis of the dynamic-relative displacement of neighbor atoms details the correlation of the lattice vibrations fading with the increase of atom-pair distance. Negative correlations are revealed from displacements of far-neighbor atoms with pair direction normal to the crystal surface, which we explain as breathing vibration modes. We propose a phenomenological dynamical model to predict the influence of material structure and NCs shape on the dynamic lattice distortion. Lattice vibrations show a marked dependence on the atom-pair direction, which enhances with decreasing size and cubic shape of crystals. Our work demonstrates that, if proper distortion models are used, the thermal motion of atoms near the surface of metallic NCs can be observed from total scattering data. Further simulations and experiments will support the future extension to compositionally and architecturally complex nanoparticles of the anisotropic lattice distortion model (ALDi) that is here introduced.

Structure and dynamic simulation-based interactions of benzenoids, pyrroles and organooxygen compounds for effective targeting of GPX4 in ischemic stroke

The discovery of a novel drug for ischemic stroke is plagued by expensive and unsuccessful outcomes. FDA-approved drugs could be a viable repurposing strategy for stroke therapy. Emerging evidence suggests the regulating role of Glutathione peroxidase (GPX4) in stroke and attracts as a potential target. To overcome limited therapeutic interventions, a drug repurposing in silico investigation of FDA-approved drugs is proposed for the GPX4 receptor in distinctive species (Homo sapiens and Mus musculus). The GPX4 UniProt wild type ids, that is, P36969 (Homo sapiens), P36970 (Rattus norvegicus) and O70325 (Mus musculus) are Swiss modelled, and resultant templates are 2OBI and 6HN3 for Homo sapiens, and 5L71 for Mus musculus with a sequence identity of ∼88%. Enrichment analysis reveals high sensitivity and ranked actives with ROC and AUC values of 0.59 and 0.61, respectively. Virtual screening at extra precision resulted hit Acarbosum, is similar between 2OBI and 6HN3, demonstrating a multiple-target specificity and Iopromide, targeting 2OBI. MD simulation at 100 ns following trajectory analysis provides RMSD (∼1.2–1.8Å), RMSF (∼1.6–2.7Å), Rgyr (∼15–15.6Å) depicting stabilisation of receptor–ligand complexes. Furthermore, average B-factor value of 2OBI, 6HN3 and 5L71 is 25Å, 24Å and 60Å with a defined resolution of 1.55Å, 1.01Å and 1.80Å, respectively, depicting the thermodynamic stability of the protein structures. The dynamic cross-correlation and principal component analysis of residual fluctuations reveal more positive correlation, high atomic displacements and greater residual clustering of residues from atomic coordinates. Therefore, Acarbosum, an FDA-approved drug, could act as a potential repurposing drug with a multi-target approach translating from preclinical to clinical stages. Communicated by Ramaswamy H. Sarma

Atomistic assessment of structural evolution for magnesium during hypervelocity nanoprojectile penetration.

In the present study, investigating the effect of ballistic penetration of spherical projectiles on a monocrystalline magnesium specimen is performed using embedded atom method (EAM) potential in molecular dynamics (MD) simulation. The dynamic investigations of structural evolution based on common neighbor analyses and Wigner-Seitz defect analysis are carried out for the varying depths of penetration and velocities of the projectile (v = 2kms-1, 6kms-1, and 10kms-1). It is found that the extent of amorphization in the specimen is more in the case of higher depth and lower projectile velocity. Voronoi cluster analyses are also done to identify cluster distribution and their transformation during ballistic penetration, which is accompanied by atomic strain and displacement vector evaluation to give light to the effect of shear strain and displacement of atoms respectively. According to Voronoi cluster analysis, Voronoi polyhedra having < 0, 4, 4, 6 > and < 0, 6, 0, 8 > clusters exhibit a higher population during hypervelocity projectile penetration. The findings have potential applications in hypervelocity applications such as defense and space technologies.

The lattice distortion, mechanical and thermodynamic properties of A(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 (A = Sr, Ba) high-entropy perovskite with B-site disorder: First principles prediction

High-entropy perovskite oxides are novel high-entropy ceramics developing recently. In this work, the local lattice distortion, mechanical and thermodynamic properties of perovskites A(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 (A = Sr, Ba) are explored using the first principle investigation. The equilibrium lattice parameter and bulk moduli of high-entropy perovskites obtained by fitting approximately satisfy the rule of mixture of the components, while the entropy effect of component mixing is very small. The bond length distribution reveals the B-site disorder results in large local lattice distortion. The atomic displacement indicates larger average displacement of O atoms contributes mainly to the wider bond length distribution for most B-O bond. The distortion degree at B-site is naturally associated with A-site. The obtained elastic constants of high-entropy perovskites are also closed to the rule of mixing of the components. Compared with ternary SrTiO3 and BaTiO3 perovskites, B-site mixing for high-entropy perovskites enhances their toughness at expense of strength and stiffness, showing the elastic moduli can be modified and adjusted through multi-component design strategy. Relevant thermodynamic property reveals the B-site disorder is benefit to improve the resistance to softening and suppress volume expansion at high temperature. Electronic structures show the insulator–metal transition takes place, also uncover that the interaction of B-O bond is stronger.

SiO2 etching and surface evolution using combined exposure to CF4/O2 remote plasma and electron beam

Electron-based surface activation of surfaces functionalized by remote plasma appears like a flexible and novel approach to atomic scale etching and deposition. Relative to plasma-based dry etching that uses ion bombardment of a substrate to achieve controlled material removal, electron beam-induced etching (EBIE) is expected to reduce surface damage, including atom displacement, surface roughness, and undesired material removal. One of the issues with EBIE is the limited number of chemical precursors that can be used to functionalize material surfaces. In this work, we demonstrate a new configuration that was designed to leverage flexible surface functionalization using a remote plasma source, and, by combining with electron beam bombardment to remove the chemically reacted surface layer through plasma-assisted electron beam-induced etching, achieve highly controlled etching. This article describes the experimental configuration used for this demonstration that consists of a remote plasma source and an electron flood gun for enabling electron beam-induced etching of SiO2 with Ar/CF4/O2 precursors. We evaluated the parametric dependence of SiO2 etching rate on processing parameters of the flood gun, including electron energy and emission current, and of the remote plasma source, including radiofrequency source power and flow rate of CF4/O2, respectively. Additionally, two prototypical processing cases were demonstrated by temporally combining or separating remote plasma treatment and electron beam irradiation. The results validate the performance of this approach for etching applications, including photomask repair and atomic layer etching of SiO2. Surface characterization results that provide mechanistic insights into these processes are also presented and discussed.

Synthesis, crystal structure, photoluminescence of Ba3Y2(BO3)4:Er3+ and thermal expansion of Ba3Y2(BO3)4

The Ba3Y2–xErx(BO3)4 (х = 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphors were obtained by crystallization from a melt. The Ba3Y2(BO3)4 crystal structure was refined from single crystal X-ray diffraction data to R = 0.037. Its anisotropic atomic displacement parameters for all atoms were refined for the first time. The borate crystallizes in the orthorhombic crystal system, space group Pnma with unit cell parameters a = 7.673(1), b = 16.44(1), c = 8.977(2) Å, V = 1132.3(3) Å3, Z = 4. These phosphors are isotypical to those of the A3M2(BO3)4 (A = Ca, Sr, Ba, M = Ln, Y, Bi) family. The crystal structure contains the isolated BO3 triangles, two general and a special one independent crystallographic sites for large cations, which are disordered over sites. Thermal behavior of Ba3Y2(BO3)4 was investigated by high-temperature X-ray powder diffraction and thermal expansion coefficients are calculated in a wide temperature range. An inflections of temperature dependencies of the unit cell parameters is observed in a range 600–740 °C. Luminescence spectra, excitation and kinetic curves of the Ba3Y2(BO3)4:Er3+ series are reported. A maximum luminescence intensity is observed for the x = 0.1 sample. According to vibrational spectroscopy data no structural changes upon activation of the Ba3Y2(BO3)4 matrix with the Er ions are observed.

Strong modulation of carrier effective mass in WTe2 via coherent lattice manipulation

The layered transition-metal dichalcogenide WTe2 is characterized by distinctive transport and topological properties. These properties are largely determined by electronic states close to the Fermi level, specifically to electron and hole pockets in the Fermi sea. In principle, these states can be manipulated by changes to the crystal structure. The precise impact of particular structural changes on the electronic properties is a strong function of the specific nature of the atomic displacements. Here, we report on time-resolved X-ray diffraction and infrared reflectivity measurements of the coherent structural dynamics in WTe2 induced by femtosecond laser pulses excitation (central wavelength 800 nm), with emphasis on a quantitative description of both in-plane and out-of-plane vibrational modes. We estimate the magnitude of these motions, and calculate via density functional theory their effect on the electronic structure. Based on these results, we predict that phonons periodically modulate the effective mass of carriers in the electron and hole pockets up to 20%. This work opens up new opportunities for modulating the peculiar transport properties of WTe2 on short time scales.