Crystal Lattice Defects Research Articles

Bicanonical ensemble Monte Carlo simulation of water condensation in the field of crystal lattice defects

The free energy, formation work and entropy dependences for water condensate formed from the vapor over the defect-free and containing surface defects basal face of β-AgI crystal at initial stage of condensation at temperatures of 260 K and 400 K are calculated using the bicanonical statistical ensemble method, with Ewald summation for long-range electrostatic and polarization interactions with the substrate. The effect of surface defects in form of rectangular “towers” as a part of regular structure on the stability of condensed phase embryos is investigated. In contrast to small-scale structures, relatively larger coarse-grained nanostructure of crystal surface demonstrates an unconditional advantage in the ability to stimulate condensation compared to defect-free surface. The formation of condensed phase embryos on the surface with multiple defects begins at vapor pressures 5–6 orders of magnitude lower than that on corresponding defect-free surface, and this effect is resistant to temperature variations. The condensate on the surface of the crystal is thermodynamically stable, both on defect-free and nanostructured surfaces, with the exception of short initial stage of the monomolecular film on the defect-free surface.

Mineral dissolution and reprecipitation mediated by an amorphous phase

Fluid-mediated mineral dissolution and reprecipitation processes are the most common mineral reaction mechanism in the solid Earth and are fundamental for the Earth’s internal dynamics. Element exchange during such mineral reactions is commonly thought to occur via aqueous solutions with the mineral solubility in the coexisting fluid being a rate limiting factor. Here we show in high-pressure/low temperature rocks that element transfer during mineral dissolution and reprecipitation can occur in an alkali-Al–Si-rich amorphous material that forms directly by depolymerization of the crystal lattice and is thermodynamically decoupled from aqueous solutions. Depolymerization starts along grain boundaries and crystal lattice defects that serve as element exchange pathways and are sites of porosity formation. The resulting amorphous material occupies large volumes in an interconnected porosity network. Precipitation of product minerals occurs directly by repolymerization of the amorphous material at the product surface. This mechanism allows for significantly higher element transport and mineral reaction rates than aqueous solutions with major implications for the role of mineral reactions in the dynamic Earth.

Definition of the aging process parameters for nickel hydroxide in the alkaline medium

The parameters of theaging process of nickel hydroxide in thealkali medium, depending on aging time and presence of cobalt hydroxide additive, have been determined. It was revealed that theaging process is governed by re-crystallization of nickel hydroxide and it also occurs through theordering of crystal lattice defects, including in the direction along (001) plane. It was determined that aging results in a significant decrease of theutilization coefficient of nickel hydroxide. It was also revealed that theaging rate is high initially, but decreases overtime. It was determined that theutilization coefficient for nickel hydroxide with and without cobalt hydroxide had decreased by 37 % and 47 %, respectively, after aging in 4.5МКОНfor 56 days. The mechanism describing thechange of theaverage discharge potential for theaged samples with cobalt hydroxide has been proposed. It is assumed that aging of nickel hydroxide with cobalt hydroxide leads to theformation of a layered double hydroxide film on thesurface of nickel particles.

Petrography and geochemical composition of the middle Eocene, the Shahabazan Formation at Kialu Section, Zagros Basin, Southwestern Iran

The Shahbazan Formation at Kialu section in the Zagros Basin, south-west of Iran, is composed mainly of carbonates with the age of middle Eocene. This formation, with a thickness of 240 m, consists of thick carbonates which pervasively dolomitized. On the basis of petrographic and geochemical features, four different replacive and cement dolomite phases have been recognized. Cathodoluminescence and scanning electron microscope were used to study time of cementation and diagenetic feature as well as to illustrate fine dolomite crystals which are not visible under common microscope. Cathodoluminescence figures show growth zonation and a rimmed bright green luminescence of syntaxial overgrown dolomite as a diagenetic cement as well as some kinds of lattice defects in some cement crystals. Inside-out dolomites seen by applying scanning electron microscope have been interpreted as a result of meteoric diagenesis, caused dissolution of dolomites during exposure. Geochemical analysis of major elements including Mg2+ and Ca2+ and trace elements such as Sr, Na, Mn2+ and Fe2+ with a trend of decreasing in Sr and increasing in Na, Mn2+ and Fe2+ during burial diagenesis, along with the cement zonation, visible under cathodoluminescence microscope, indicate dolomite purification and recrystallization under reducing condition.

КРИСТАЛЛОХИМИЧЕСКИЕ АСПЕКТЫ ОЦЕНКИ ЭНЕРГИИ ВЗАИМОДЕЙСТВИЯ ЧАСТИЦ ГЛИНИСТЫХ МИНЕРАЛОВ

The goal of the paper is to analyze the changes in mineral crystal lattice under acid activation. Methods. Clay from the Slyudyanka deposit is the material under investigation. The methods used in the study include x-ray phase analysis using Bruker D8 Advance diffractometer. The diffractogram is recorded using the EVA program installed on a PC in combination with the diffractometer. The quantitative composition is calculated using the Topas 3.0 program. The study also uses the methods of scanning microscopy of the oriented sample, titrimetric analysis methods (the methods of neutralization and complexometry 0; conductivity measurement (determination of solution electrical conductivity); potentiometric measurements (determination of electrokinetic potential at electrophoresis); sedimentation analysis in gravitational and centrifugal fields. Modern databases and Excel are used for thermodynamic calculations. Results. Crystallochemical analysis of mineral structure and thermodynamic assessment of process spontaneous flow conditions allowed to explain the nature of the potential curve after acid activation of the clay from the Slyudyanka deposit. The extreme nature of this dependence is associated with the changes in the field of force on the surface of particles as a result of the flow of the complex of physico-chemical interactions, the most important of which are interactions of backbone ions with the components of environment. In its turn, the changes in the interaction energy of clay particle weight calculated by the results of colloid-chemical studies allow to analyze the processes occurring in the crystal lattice of clay under acid activation. Experimental data confirm the similarity of some patterns of acid activation of clay minerals associated to the fact that the process is accompanied by the washout of ions from the crystal lattice skeleton and formation of structure defects. The defects of crystal lattice causing the disturbance of its regularity, the transition of surface silica in amorphous state provide the change in both system dispersion and porosity of clay samples. Conclusions. It is more preferable to use the acid activation for the production of mineral sorbents with developed porosity when minerals with an expanding structural cell are used as a source material.

A system of experimental studies of electric properties of rocks in the inert medium

In the work presented, the construction and the hardware-methodological features of the automated measuring system developed and realized at the Institute of Geophysics of the National Academy of Sciences of Ukraine designed to study electrical parameters of the mineral substance at temperatures up to 1100 °C in oxygen-containing and inert media are described in detail. The results of some experiments performed at the stage of experimental tests of the complex in the temperature range from room temperature to 700 °C are shown. The factors influencing the character of the obtained temperature-frequency dependences of the electrical parameters of the investigated samples are considered and analyzed. It is shown that the formation of oxides in an oxygen-containing medium increases the electrical resistance. The difference in the gradient of the change in r from the temperature, especially in the range 300—500 °C, is due to the fact that the electrical conductivity is carried out mainly by impurity ions and crystal lattice defects. As the temperature is raised, the dielectric constant of ionic crystals increases, which is due to the weakening of the bond between the individual ions. Low-frequency permittivity is the most sensitive to deformation phase transitions and is a more informative parameter, since it varies with a larger gradient.

Model of superconductivity formation on ideal crystal lattice defect–twin or twin boundary (MSC-TB)

The report provides a review of the experimental material on superconductivity (SP) accumulated by 2017, a critical analysis of the Bardeen-Cooper-Schrieffer theory (BCS) has been given, and a new model of the super-conductivity effect proposed in works of V.A. Chizhov has been presented. The new model allows to understand the mechanism of the SP formation and to explain many experimental facts on the basis of the theory of pro-cesses occurring in the ideal defect of the crystal lattice – the twinning boundary (MSC-TB). Specific materials, including new ones, are described, which, in accordance with the theory of MSC-TB, should have improved properties of SC, promising directions for further research are formulated.

How reproducible are kinetic parameter constraints of quartz luminescence? An interlaboratory comparison for the 110 °C TL peak

Knowledge of the kinetic parameters E (thermal activation energy) and s (frequency factor) of charge-trapping defects in the quartz crystal lattice is of paramount importance to assessing the thermal stability of associated luminescence signals used for dosimetry and dating. Since methods proposed for constraining thermoluminescence (TL) kinetics usually make use of the signal response to thermal treatments, accurate temperature control is required to obtain valid E and s values. In an attempt to check the extent to which consistent kinetic parameters could be obtained using routine luminescence measurement equipment, we have investigated three methods (isothermal decay, initial rise and the Hoogenstraaten method) in an inter-comparison study involving eight laboratories using Risø and Freiberg Instruments systems. The target signal was the so-called 110 °C TL peak of a sample of Oligocene coastal dune quartz sand from the Fontainebleau sand formation (France).TL glow curves recorded with heating rates in the range 0.02–5 K s−1 showed peak positions varying up to 60 °C between systems at the highest heating rates, attributed to temperature calibration errors and/or thermal lag. Kinetic parameters derived from the complete data set show a large spread, covering the ranges ∼0.5–1.2 eV and 106–1017 s−1 for E and s. In most cases, interlaboratory variations exceeded those of replicate measurements within individual laboratories. Signal lifetimes at 20 °C derived from the isothermal decay (∼59 min) and initial rise methods (at low heating rates; ∼60–80 min) most closely match the value directly measured at 20 °C from within two luminescence readers (∼70 min). Finally, we discuss the consequences of these findings for dosimetry and dating using luminescence signals and possible ways to reduce systematic errors in laboratory measurements of kinetic parameters.

Grain Boundary Modification via F4TCNQ To Reduce Defects of Perovskite Solar Cells with Excellent Device Performance.

Solar cells based on hybrid organic-inorganic metal halide perovskites are being developed to achieve high efficiency and stability. However, inevitably, there are defects in perovskite films, leading to poor device performance. Here, we employ an additive-engineering strategy to modify the grain boundary (GB) defects and crystal lattice defects by introducing a strong electron acceptor of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) into perovskite functional layer. Importantly, it has been found that F4TCNQ is filled in GBs and there is a significant reduction of metallic lead defects and iodide vacancies in the perovskite crystal lattice. The bulk heterojunction perovskite-F4TCNQ film exhibits superior electronic quality with improved charge separation and transfer, enhanced and balanced charge mobility, as well as suppressed recombination. As a result, the F4TCNQ doped perovskite device shows excellent device performance, especially the reproducible high fill factor (up to 80%) and negligible hysteresis effect.

The influence of high-energy ball milling on the heterogeneous reaction kinetics in the Ti-Si system

The high-temperature (1300–1600 K) kinetics for the Ti-Si reactive system were investigated using electro-thermal analysis. The influence of short-term (1–3 min) high-energy ball milling (HEBM) of Ti+0.6Si heterogeneous powder mixtures on the kinetic parameters was also studied. It was shown that HEBM leads to a significant decrease of the apparent activation energy (Ea) of the solid-state reaction between silicon and titanium. For the non-milled mixture, Ea is 339 ± 63 kJ/mol, while after 3 min of HEBM it drops more than twice to 148 ± 12 kJ/mol. The reaction initiation temperature also decreases with an increase of HEBM time: from 1467 ± 62 K for the pristine mixture to 1110 ± 42 K after 3 min of mechanical treatment. The conclusion was made that a decrease of crystalline size and an increase of the crystal lattice defect concentration, which in combination enhance the grain boundary diffusion, can be responsible for the high reactivity of the mechanically activated mixtures.

Control of HAp Formation and Osteoconductivity on Nitrogen-Doped TiO<sub>2</sub> Scale Formed by Oxynitridation of Ti

The surface potential of the TiO2 scale formed on Ti was controlled by varying the Ti heat treatment conditions in a N2 atmosphere containing a trace amount of O2. The surface potential was attributed to the effective charge of nitrogen-related defects in the TiO2, where the positive and negative surface charges were associated with (N2)0+2 and (NO)0-1, respectively. The latter defects were formed only during the early stages of the heat treatment, and with increasing treatment time, this was followed by the formation of voids containing N2 in the scale rather than the disappearance of the defects in the TiO2 crystal lattice, resulting in zero surface charge. Hydroxyapatite (HAp) formation and osteoconductivity were enhanced on nitrogen-doped TiO2 scale with either a positive or negative surface potential. In contrast, for the unchanged TiO2 scale, no HAp formation was observed and the osteoconductivity was low.

Influence of uniaxial pressing and nickel catalytic additive on activation of magnesium hydride thermal decomposition

Speed-up of thermal decomposition of magnesium hydride due to uniaxial pressing, including pressing in presence of nickel catalyst, was studied by barometry, SEM, DSC, XRD methods, and using mathematical modeling. Pressing even with no catalyst is shown to hasten the hydrogen desorption. The most probable reason for this is the formation of multiple defects in crystal lattice. They can serve as nucleation centers: metal nuclei significantly hasten hydrogen desorption. Besides, metal magnesium not converted to the hydride during the synthesis stage can possibly appear at surface. Adding nickel powder before pressing hastens dehydriding process even more. Comparing hydrogen evolution curves for samples with different amount of nickel allowed to propose the probable mechanism of hydrogen evolution. It is based on description of reactions of hydrogen desorption and hydride decomposition and of the metal-hydride phase morphology change due to these reactions. We develop a mathematical model in form of ordinary differential equations that fits the experimental data well. The model is based on conservation and symmetry assumptions. The fitting allowed to evaluate rate parameters of hydride phase decomposition.

Controllable Virus-Directed Synthesis of Nanostructured Hybrids Induced by Organic/Inorganic Interactions.

The bioinspired synthesis of hierarchical hybrid nanomaterials using biological objects as a template attracts growing interest for the design of new technologically relevant nanostructured materials. To ensure control over the shape and properties of the fabricated hybrid structures, understanding of the growth mechanism is required. In this work, tobacco mosaic virus (TMV) is used as a template to direct the synthesis of zinc sulfide (ZnS) at ambient conditions and different pH from additive-free aqueous solution. TMV/ZnS hybrid nanowires or thin films are obtained with controllable thickness of the inorganic layer. The deposition mechanism is studied by monitoring the optical properties, band gap (Eg ) and particle size, respectively, of ZnS particles mineralized on the TMV template and ZnS reference nanoparticles. A heterogeneous nucleation of the inorganic phase on the template surface is proposed. Band gap measurements reveal that the average size of the ZnS nanoparticles grown on the virus surface is smaller compared to solution-grown nanoparticles. Moreover, a blue shift of the ZnS photoluminescence peak indicates a dominance of different crystal lattice defects in both systems. The present method for the selective template-directed mineralization opens new possibilities in the synthesis of well-organized functional hybrid materials.

Relation of Crystallinity and Fluorescent Properties of LaF3 :Nd3+ Nanoparticles Synthesized with Different Water-Based Techniques

We use two water based synthetic approaches to LaF3:Nd3+ nanoparticles (NPs), hydrothermal microwave treatment (HTMW) and co-precipitation (CO) technique, with different temperature of the reaction mixture to study the correlation between the degree of crystallinity of LaF3:Nd3+ NPs and their fluorescence properties. We showed that the fluorescence spectra and quenching kinetics can be a powerful tool to reveal the crystal lattice defects, namely agglomerations of the dopant ions (Nd3+) and the OH− positioned in the volume of the doped NPs. We found that reduced number of such crystal lattice defects as Nd3+ pairs and clusters and the OH groups in the volume of the HTMW NPs leads to much higher fluorescence brightness than for CO NPs. The higher temperature of reaction mixture during HTMW synthesis results in better crystallinity and much higher fluorescence brightness of the produced NPs. But we believe that these results could be applied more generally to the development of synthetic strategies for bright fluorescent NPs. In sum, it's not the condition of NPs surface, but the degree of their crystallinity should be a major concern while choosing the synthetic path, as it generally predetermines their fluorescent properties.

Electron transfer in the structure of a photorefractive doped Bi12TiO20: Ru crystal

The ac conductivity of Bi12TiO20: Ru crystals has been studied in the frequency range 102–106 Hz and at temperatures 293–773 K. The experimental data have been analyzed in the framework of the model of correlated barrier hops. In this material, the potential barriers are due to the existence of a block structure, crystal lattice defects, and also the presence of a ruthenium impurity. The microparameters characterizing the charge transfer in doped bismuth titanate single crystals have been determined.

ZrO2 quantum dots/graphene phototransistors for deep UV detection

ZrO2 is a promising material for deep-UV detection application, yet the low carrier density and high crystal lattice defects hinder the device performance. Graphene is an attractive material for photoactive and charge transport layers in photodetectors, but the photoresponsivity have been limited by the weak light absorption, no wavelength selectivity. Here, we demonstrate heterostructure phototransistors consist of graphene as the conducting channel, which is covered by a film of ZrO2 quantum dots as the light absorption layer. Light absorption in the quantum dots layer creates electron-hole pairs. Under the built-in electric field, the electrons are trapped in ZrO2 acting as an additional light tunable gate, whereas the holes are transferred towards the graphene. The ZnO2/Graphene heterostructure, with a high photoresponsivity of 22AW−1 and wavelength selectivity to deep UV wavelength range (220–250nm) at low operating voltage, is promising to be integrated into solution processed and low-cost optoelectrical devices.

Photon echoes as means of studying defective surface structure of the crystal fibers of thin films

Dependences of the decay of stimulated photon echoes excited in thin textured p- and n-type zinc oxide and silicon films characterized by different sizes of crystal fibers are studied. Two characters of recombination were revealed for localized excitons on crystal lattice defects, presented in the studied dependences in the form of fast and slow decay components.

Investigation of Ion-Mediated Charge Transport in Methylammonium Lead Iodide Perovskite

We have investigated the origin of ionic conductivity in methylammonium lead iodide (MAPbI3) by positron annihilation lifetime spectroscopy (PALS), supplemented by coincidence Doppler broadening spectroscopic (CDBS) techniques which reveal the presence of methylammonium (MA+) defects in the perovskite crystal lattice. Crystallinity and the defect concentration vary with the perovskite synthesis process, which in turn governs the magnitude of ionic conductivity. Single-crystalline perovskite contains lesser defects with equal probability of developing both cationic and anionic (halide) vacancies, whereas the polycrystalline perovskite sample developed through mechanical process carries mainly cationic, i.e., MA+ vacancy (V′MA) in its crystal lattice as indicated by direct current (dc) polarization experiment.

Defect mode and crystal-electric-field effects on the thermal expansion and heat capacity of RB50 boride

Specific heat and thermal expansion in LuB50 and TbB50 borides at 2–300 K were experimentally studied. In both compounds, for a large range of low temperatures a negative thermal expansion caused by defects in the crystal lattice was observed. The effect of the crystal electric field on the thermal characteristics of TbB50 was observed as a Schottky anomaly in the temperature dependence of the heat capacity and as an additional negative contribution to the thermal expansion. The analysis of the heat capacity data suggests that the ground state of the ion Tb3+ is a quasi-quintet, consisting of close-located singlet and two doublets. The phase transition of TbB50 to the antiferromagnetic state appears as a very weak broad anomaly in the temperature dependence of the heat capacity; within the scattering of the experimental data, it is not visible in the temperature dependence of the unit cell volume.

Electrical detection of diamond defects.

Optoelectronics![Figure][1] Crystal lattice defects in diamonds make various optoelectronic applications possible. PHOTO: IMAGEBROKER/ALAMY STOCK PHOTO Diamonds have many different kinds of defects, each type imbuing the crystal with a distinctive color. The quantum properties of the