Real Crystals Research Articles

Inverse Design of Ultralow Lattice Thermal Conductivity Materials via Materials Database Screening of Lone Pair Cation Coordination Environment.

The presence of lone pair (LP) electrons is strongly associated with the disruption of lattice heat transport, which is a critical component of strategies to achieve efficient thermoelectric energy conversion. By exploiting an empirical relationship between lattice thermal conductivity, κL, and the bond angles of pnictogen group LP cation coordination environments, we develop an inverse design strategy based on a materials database screening to identify chalcogenide materials with ultralow κL for thermoelectrics. Screening the ∼635 000 real and hypothetical inorganic crystals of the Open Quantum Materials Database based on the constituent elements, nominal electron counting, LP cation coordination environment, and synthesizability, we identify 189 compounds expected to exhibit ultralow κL. As a validation, we explicitly compute the lattice dynamical properties of two of the compounds (Cu2AgBiPbS4 and MnTl2As2S5) using first-principles calculations and successfully find both achieve ultralow κL values at room temperature of ∼0.3-0.4 W/(m·K) corresponding to the amorphous limit. Our data-driven approach provides promising candidates for thermoelectric materials and opens new avenues for the design of phononic properties of materials.

General electron theory of reduction and oxidation of metals

The significance of the new theory of metal reduction from ores has been demonstrated. It was shown that all the existing versions of the theory are based on atomic-molecular representations of the early 20-th century where reduction is considered as a process of exchange of oxygen atoms between a reducing agent and oxide molecules. These representations do not take into account changes in the crystalline structure of oxides and in the state of a gas medium with change in temperature and pressure. The attention here was drawn to the absence of molecules in oxides, and atoms in metals. Inconsistency of a number of the theory conclusions with practice of reduction during operation of plants was revealed. Based on the assumptions of redox reactions as processes of exchange of reagents by the valence electrons, defective ionic structure of real crystals, changes in the state of the gaseous medium during heating and pressure increase using some statements of quantum mechanics on the distribution of electrons in solids, the authors have developed electron version of the reduction theory. This theory is based on the unity of the anionic sublattice of all crystals of the oxide phase and the collective electronic system of all valence electrons of metal cations in oxide. It is shown that in the reduction plants, due to the thermal ionization of gases and thermionic emission from the surface of the heated bodies, the gas medium is plasma. The presence of charged particles in the plasma ensures their interaction at a considerable distance and the course of chemical processes in the kinetic mode. The gaseous reduction products are removed from the reaction zone with exhaust gases, and the electrons released in the plasma are absorbed by the oxide surface and exist in the oxide together with the anionic vacancies that arise when oxygen is removed. In high-grade ores the vacancies merge and disappear on the oxide surface, and the free electrons of the vacancies combine the nearest cations with a metal bond to form a metal shell which later turns into carbides. The formation of carbide shells blocks the oxide surface and stops reduction. When temperature rises and the shells melt the reduction process resumes. Therefore, the carbon-thermal reduction produces cast iron and high-carbon ferroalloys. In low-grade and complex ores the vacancies are scattered in the oxide volume along the total anionic sublattice forming solution of vacancies and free electrons. The vacancies merge and disappear in places of increased concentration of cations where the Fermi level of atoms is less than the chemical potential of the free electrons. In the formed anionic void the free electrons rearrange metal cations with low Fermi energy and bind them with a metal bond bypassing the stage of atom formation. Crystal growth in an anionic void occurs without resistance from the parent oxide phase.

Orbital ordering of ultracold alkaline-earth atoms in optical lattices

We report on a dynamical mean-field theoretical analysis of emerging low-temperature phases in multicomponent gases of fermionic alkaline-earth(-like) atoms in state-dependent optical lattices. Using the example of $^{173}$Yb atoms, we show that a two-orbital mixture with two nuclear spin components is a promising candidate for studies of not only magnetic but also staggered orbital ordering peculiar to certain solid-state materials. We calculate and study the phase diagram of the full Hamiltonian with parameters similar to existing experiments and reveal an antiferroorbital phase. This long-range-ordered phase is inherently stable, and we analyze the change of local and global observables across the corresponding transition lines, paving the way for experimental observations. Furthermore, we suggest a realistic extension of the system to include and probe a Jahn-Teller source field playing one of the key roles in real crystals.

Dispersion of Light in the 1D Photonic Crystal

We propose a novel, Kurosawa-like model to evaluate the 1D (Bragg stack-like) mesoporous aluminium oxide photonic crystal. To do this, we analyze the internal potential of the photonic crystal superlattice and get it describing the set of the medium’s polar oscillators. Unlike the atomic oscillators for a common crystal, these ones are the abstract ones. This way, the real photonic crystal can be dealt as an abstract oscillators’ ensemble. The result is fully agreed with the thermodynamics, and makes the theory very powerful. To obtain the oscillators parameters, we compare the theory with the secondary emission spectrum of the crystal, and get the natural frequency and the force for each oscillator. This phenomenological approach allow us to calculate photonic crystal’s optical characteristics, such as the dispersion law for the light in the nanostructure, the secondary emission spectrum of the composite, the speed of light in the crystal and the effective mass of the speed quanta. We establish the room-temperature Bose-Einstein condensation of polaritons in crystal at the photonic bandgap edge. The results are important to the solid-state detection of paraphotons.

A simplified model to predict resistivity profiles in continuous-feeding Cz-silicon crystals

The Continuous-feeding Czochralski (CCz) method and an apparatus comprising multiple quartz crucibles have recently been used to manufacture commercial silicon single-crystals for microelectronics. This paper describes a practical method for calculating and predicting the resistivity in the CCz-silicon crystal as a function of the initial dopant concentration in the silicon melt, the pull rate, the crystal mass and the amount of dopant regularly added to the melt during the growth process. This simplified model considers and includes the silicon mass transport from the outer crucible to the inner crucibles, the concentration of the dopant species added to the melt, the evaporation of the dopant (for volatile species), the impurity segregation to the crystal. Data collected from real crystals grown with the CCz method by using three separated melt zones are also reported here for a comparison with the model.

Dynamics of particulate assemblages in metastable liquids: a test of theory with nucleation and growth kinetics.

This manuscript is devoted to the nonlinear dynamics of particulate assemblages in metastable liquids, caused by various dynamical laws of crystal growth and nucleation kinetics. First of all, we compare the quasi-steady-state and unsteady-state growth rates of spherical crystals in supercooled and supersaturated liquids. It is demonstrated that the unsteady-state rates transform to the steady-state ones in a limiting case of fine particles. We show that the real crystals evolve slowly in a more actual case of unsteady-state growth laws. Various growth rates of particles are tested against experimental data in metastable liquids. It is demonstrated that the unsteady-state rates describe the nonlinear behaviour of experimental curves with increasing the growth time or supersaturation. Taking this into account, the crystal-size distribution function and metastability degree are analytically found and compared with experimental data on crystallization in inorganic and organic solutions. It is significant that the distribution function is shifted to smaller sizes of particles if we are dealing with the unsteady-state growth rates. In addition, a complete analytical solution constructed in a parametric form is simplified in the case of small fluctuations in particle growth rates. In this case, a desupercooling/desupersaturation law is derived in an explicit form. Special attention is devoted to the biomedical applications for insulin and protein crystallization. This article is part of the theme issue 'Patterns in soft and biological matters'.

Experimental probe of a complete 3D photonic band gap.

The identification of a complete three-dimensional (3D) photonic band gap in real crystals typically employs theoretical or numerical models that invoke idealized crystal structures. Such an approach is prone to false positives (gap wrongly assigned) or false negatives (gap missed). Therefore, we propose a purely experimental probe of the 3D photonic band gap that pertains to any class of photonic crystals. We collect reflectivity spectra with a large aperture on exemplary 3D inverse woodpile structures that consist of two perpendicular nanopore arrays etched in silicon. We observe intense reflectivity peaks (R>90%) typical of high-quality crystals with broad stopbands. A resulting parametric plot of s-polarized versus p-polarized stopband width is linear ("y=x"), a characteristic of a 3D photonic band gap, as confirmed by simulations. By scanning the focus across the crystal, we track the polarization-resolved stopbands versus the volume fraction of high-index material and obtain many more parametric data to confirm that the high-NA stopband corresponds to the photonic band gap. This practical probe is model-free and provides fast feedback on the advanced nanofabrication needed for 3D photonic crystals and stimulates practical applications of band gaps in 3D silicon nanophotonics and photonic integrated circuits, photovoltaics, cavity QED, and quantum information processing.

Solubility of Gold in Common Gold-Concentrating Minerals

Abstract —The paper is a summary of the authors’ and published data on the occurrence of Au in common gold-concentrating minerals (pyrite, arsenopyrite, pyrrhotite, chalcopyrite, bornite, galena, sphalerite, and magnetite). The solubility of gold in minerals is evaluated through identification of the limiting element incorporation into the real crystal. The distribution of gold between coexisting minerals is considered. Obtaining reliable data on the gold solubility involves discrimination of the structural form of the element and correct separation of Au forms between the surface and the volume, which is not always possible because of the small size and low quality of crystals (defects and highly developed internal surfaces). It is also necessary to have a phase (individual or nonautonomous) limiting the incorporation of Au or to compare the mineral under study (within the framework of the principle of phase composition correlation) with a reference mineral with a reliably established structural form of Au. The most reliable and consistent estimates for the hydrothermal parameters (450–500 ºC, 1 kbar) are as follows (µg/g): sphalerite – 0.7, highly ferrous sphalerite – 5, magnetite – 1, pyrite – 3, manganese and copper-containing pyrite – 10, pyrrhotite – 21, chalcopyrite – 110, bornite – 140, and galena – 240. The highest solubility of gold (up to 30,000 µg/g) is established in arsenopyrite, but it is likely to be a metastable miscibility caused by the nonstationary conditions of crystal growth or by the crystal growth at the expense of the surficial nonautonomous phase. The same factors can cause supersaturation of pyrite with Au admixture at low temperatures. The dual behavior of Au in pyrrhotite and magnetite is for a different reason: Under reducing conditions, these minerals can contain a submicroscopic elemental form of Au indistinguishable from the structural one. We consider the forms of Au occurrence and the relationship between the solubility of gold and its metallic bonds in minerals.

Relativistic electron energy conversion in one photon in crystals

Interaction of relativistic electrons with crystal axis is traditionally described in terms of channeling model—i.e. as a motion in some homogeneous averaged axial potential. However, real crystals are made of atoms, positioned periodically. Interaction of electrons with periodical potential must be accompanied with transitions of discrete portions of momentum Δ p∥ = 2π nℏ /d, n = 1, 2, 3,ṡ, defined by the potential period d. Transmission of sufficient portion of longitudinal momentum to the lattice may be accompanied by the emission of photon with correspondingly high energy. In case of relativistic electrons with energies E1 ∼ GeV or more, nearly all the electron's energy may be converted into just one photon.

Structural Thermodynamics of Real Liquid Crystals – Cause of Stability and The Beyond

Structural Thermodynamics of Real Liquid Crystals – Cause of Stability and The Beyond

Crystal-Diffraction Method for Ultraprecision Neutron Spectrometry. Influence of the Temperature Stability and Vibration Level

A test setup for measuring the neutron electric charge using spin interferometry and the effect of the double-crystal focusing of neutrons upon Laue diffraction is described. It is shown that a considerable increase in the distance between the crystals (up to 1 m) is needed to improve the accuracy of neutron-charge measurements. This is a difficult task because the setup becomes sensitive to slight external influences (temperature, vibration, etc.). To determine the degree of these influences, temperature tests with combined (active and passive) thermal protection were carried out. It is shown that under conditions of the reactor hall with temperature fluctuations of several degrees, the experimental setup provides a temperature stability of the crystals no worse than 0.01 K and stability of the temperature differences for the crystals and between them at a level of ~0.005 K. Measurements of the vibration level in the area of the PF1b cold neutron beam at the ILL reactor (Grenoble, France) allow estimation of the rate of displacement of crystals relative to each other at a level of ~10–3 cm/s. As follows from the data obtained, the angular resolution of the setup, without taking into account the influence of the imperfection of real crystals, can be at the level of 10–3 of the Bragg-reflection width, which is ~0.001 arc-second.

Quantitative imaging of intraerythrocytic hemozoin by transient absorption microscopy.

.Hemozoin, the heme detoxification end product in malaria parasites during their growth in the red blood cells (RBCs), serves as an important marker for diagnosis and treatment target of malaria disease. However, the current method for hemozoin-targeted drug screening mainly relies on in-vitro -hematin inhibition assays, which may lead to false-positive events due to under-representation of the real hemozoin crystal. Quantitative in-situ imaging of hemozoin is highly desired for high-throughput screening of antimalarial drugs and for elucidating the mechanisms of antimalarial drugs. We present transient absorption (TA) imaging as a high-speed single-cell analysis platform with chemical selectivity to hemozoin. We first demonstrated that TA microscopy is able to identify -hematin, the artificial form of hemozoin, from the RBCs. We further utilized time-resolved TA imaging to in situ discern hemozoin from malaria-infected RBCs with optimized imaging conditions. Finally, we quantitatively analyzed the hemozoin amount in RBCs at different infection stages by single-shot TA imaging. These results highlight the potential of TA imaging for efficient antimalarial drug screening and drug mechanism investigation.

X-ray Single-Crystal Structural Analysis of a Magnetically Oriented Monoclinic Microcrystal Suspension of α-Glycine

We previously reported on a method for X-ray single-crystal structure determination from a powder sample via a magnetically oriented microcrystal suspension (MOMS). The method was successfully applied to orthorhombic microcrystals (L-alanine, P212121). In this study, we apply this method to monoclinic microcrystals. Unlike most of the orthorhombic MOMSs, monoclinic MOMSs exhibit two or four orientations with the same magnetic energy (we refer to this as twin orientations), making data processing difficult. In this paper, we perform a MOMS experiment for a powder sample of monoclinic microcrystal (α-glycine, P21/n) to show that our method can also be applied to monoclinic crystals. The single-crystal structure determined in this work is in good agreement with the reported one performed on a real single crystal. Furthermore, the relationship between the crystallographic and magnetic susceptibility axes is determined.

DEPENDENCE OF THE MEDIUM SQUARE AMPLITUDE OF ZERO VIBRATION OF ATOMS IN THE ELEMENTS OF THE PERIODIC SYSTEM OF MENDELEEV ON THE ORDER NUMBER

According to the theory of thermal vibrations of atoms in crystals and the theory of scattering of X-rays and thermal neutrons by real crystals, the root-mean-square amplitude of the zero vibration of an atom in a lattice at T = 0 K is determined by the mass of the atom and the strength of the interatomic relationship. It is inversely proportional to the product of the mass and temperature of the Debye crystal. It was found that the amplitudes of thermal (at T = 300 K) and zero (at T = 0 K) atomic vibrations in elements, like other physical properties, at moderate temperatures have the same periodic dependence on the number of elements. This is due to the weak dependence of the configuration of the external electronic shells of atoms on the temperature. The results can be used in materials science and technology to assess the strength and thermo physical characteristics of materials at cryogenic temperatures through the Debye temperature, without measuring them directly at an absolute zero temperature.

Monte Carlo Study of Rubber Elasticity on the Basis of Finsler Geometry Modeling

Configurations of the polymer state in rubbers, such as so-called isotropic (random) and anisotropic (almost aligned) states, are symmetric/asymmetric under space rotations. In this paper, we present numerical data obtained by Monte Carlo simulations of a model for rubber formulations to compare these predictions with the reported experimental stress–strain curves. The model is defined by extending the two-dimensional surface model of Helfrich–Polyakov based on the Finsler geometry description. In the Finsler geometry model, the directional degree of freedom σ → of the polymers and the polymer position r are assumed to be the dynamical variables, and these two variables play an important role in the modeling of rubber elasticity. We find that the simulated stresses τ sim are in good agreement with the reported experimental stresses τ exp for large strains of up to 1200 % . It should be emphasized that the stress–strain curves are directly calculated from the Finsler geometry model Hamiltonian and its partition function, and this technique is in sharp contrast to the standard technique in which affine deformation is assumed. It is also shown that the obtained results are qualitatively consistent with the experimental data as influenced by strain-induced crystallization and the presence of fillers, though the real strain-induced crystallization is a time-dependent phenomenon in general.

Electronic Bands and Dielectric Functions of In0.5Tl0.5I Solid State Solution with Structural Defects

We investigate an influence of the crystal structure imperfections on the electronic properties and dielectric functions of the In0.5Tl0.5I semiconductor in the frame of the density functional theory calculations. The tensor of electron effective mass m^{*}_{ij} for the InI, In0.5Tl0.5I and TlI crystals has been calculated for the valence and conduction bands at different K-points of the Brillouin zone. The dielectric functions ε(hν) of the imperfect crystals based on In0.5Tl0.5I solid state solution with iodine vacancy and a thallium interstitial atom were calculated taking into consideration the inter-band and intra-band electron transitions. The studies of the imperfect crystals reveal increased low-frequency and stationary electron conductivity with anisotropy resulted from the anisotropy of the electron effective mass tensor. Our findings explain the origin of crucial changes in the band structure by formation of the donor half-occupied levels close to the unoccupied conduction bands due to the crystal structure defects, i.e., iodine vacancy or a thallium interstitial atom. It has been shown that in the case of real crystals, in particular metal-halides, the proper consideration of defects in quantum-chemical calculations results in a better matching with experimental data and, opposite to the perfect structure calculations, gives opportunities to explain the observed phenomena.

High-Temperature Precipitation of Impurities within the Vlasov Model for Solids

It is shown that the Vlasov model for a solid describes the complexing processes when growing real crystals with allowance for the thermal growth conditions. It makes it possible (along with the classical theory of nucleation and growth of second-phase particles in solids) to calculate the defect crystal structure that was formed during the growth. It is established that the high-temperature impurity precipitation is directly related to the subsequent transformation of the defect structure when manufacturing of silicon devices. A qualitative model of the formation of electric centers is proposed, which directly relates their origin to the initial defect structure of silicon. It is shown that the concepts and principles of the Vlasov physics are absolutely applicable in solid-state physics.

Orientation Effects of Crystal Nanoislands Growing on a Dielectric Surface

Orientation effects for crystalline nanoislands growing on dielectric surfaces are considered on the assumption of van der Waals interaction in the model of orientational phase transition with allowance for real crystallization conditions.

Unsteady ballistic heat transport in harmonic crystals with polyatomic unit cell

We study thermal processes in infinite harmonic crystals having a unit cell with an arbitrary number of particles. Initially, particles have zero displacements and random velocities, corresponding to some initial temperature profile. Our main goal is to calculate spatial distribution of kinetic temperatures, corresponding to degrees of freedom of the unit cell, at any moment in time. An expression for the temperatures is derived from solution of lattice dynamics equations. It is shown that the temperatures are represented as a sum of two terms. The first term describes high-frequency oscillations of the temperatures caused by local transition to thermal equilibrium at short times. The second term describes slow changes in the temperature profile caused by ballistic heat transport. It is shown that during heat transport, local values of temperatures, corresponding to degrees of freedom of the unit cell, are generally different. Analytical findings are supported by results of numerical solution of lattice dynamics equations for diatomic chain and graphene lattice. Strong anisotropy of ballistic heat transport in graphene is demonstrated. Presented theory may serve for description of unsteady ballistic heat transport in real crystals with low concentration of defects. In particular, solution of the problem with sinusoidal initial temperature profile can be used for proper interpretation of experimental data obtained by the transient thermal grating technique.

Scaling the spatial fluctuation of spontaneous emission suppression in photonic crystals

The propagation and emission of light in a real photonic crystal is routinely affected by the intrinsic disorder and its finite-size. Thus, theoretical calculation based on the notion of a defect free crystal with an infinite thickness is irrational in the real world experiments. Here, we report an acute modification of light propagation and emission induced by the finite-size of the crystal. We have measured the emission intensity and rate from single domain of the crystal to study the finite size effect on the spontaneous emission suppression. The results show spatial fluctuation of spontaneous emission suppression across domains that have a linear scaling with crystal size. The results have implications in contriving devices pertaining to controlled spontaneous emission such as in cavity quantum electrodynamics.