MgO Crystals Research Articles

Effect of the interference between interband currents on the crystal harmonic spectra

By numerically solving the semiconductor Bloch equation, we study the high-order harmonic emission spectrum of a MgO crystal under the interaction of a linearly polarized laser pulse. Based on two-band and three-band models, by comparing the variation of the harmonic spectrum with the laser peak intensity, it is found that when the laser intensity is lower, the harmonic spectra from both cases are generally consistent above the minimum band gap. However, some harmonic intensities in the three-band model are significantly enhanced or weakened compared to the two-band case when the laser intensity is higher. By analysis of the electron population and the harmonic phase, it is demonstrated that the harmonic enhancement or reduction is caused by the interference between two interband polarization sources, one of which originates from the current between the first conduction band and the valence band and the other of which is from the polarization between the second and the first conduction band. The harmonic interference between different interband currents contains rich dynamic information and has a significant impact on the harmonic structure and yield, which is helpful for further understanding the generation mechanism of crystal harmonics.

Effects of La˗doping and preparation conditions on magnesia-based adsorption materials prepared by salicylic acid complex-combustion method for CO2 capture

Here, salicylic acid (SA) was employed as the complex-combustion aid to prepare MgO-based adsorbents (MBA) for CO2 capture. The influences of different doping content of La, calcination time and temperature, and the mole ratio of SA to metal nitrates on physico-chemical properties and CO2 adsorption capacity of as-obtained MBA were studied in detail. Under the calcination temperature lower than 550 oC and the time of 120 min, the MBA doped with 2% La showed excellent performance. As confirmed, the adsorbent which had larger surface area provided more number of basic sites. Besides, more oxygen vacancies and adsorbed OH species efficiently improved the strength of surface basicity. Finally, the micro crystals of MgO were widely separated and the durability was enhanced greatly in CO2 adsorption-desorption multiple cycles both in industrial carbon dioxide and simulated flue gas due to the dispersing of La species and the employment of SA.

Synthesis of glycine-mediated CuO–Fe2O3–MgO nanocomposites: Structural, optical, and antibacterial properties

Multi-phase metal oxides nanocomposites (NCs) have attracted considerable attention due to their extraordinary properties and novel applications over monometallic ones. Hence, trimetallic oxides nanoparticles (NPs) are preferred because of their immensely improved optical, catalytic, and biological properties, but few materials have been reported. Besides, glycine is an excellent structure-directing agent for NPs production with tailored physicochemical properties. Thus, in this work, a novel tri-phase CuO–Fe2O3–MgO (1:1:1) NCs was prepared via a sol-gel method in the presence of glycine as a fuel. The obtained NCs were characterized by Fourier transmission infrared, X-ray diffraction (XRD), Scanning electron micrographs, and UV-Vis. The XRD analysis emphasized the formation of NCs with monoclinic CuO, cubic MgO, hexagonal Fe2O3, and tetragonal CuFe2O4 crystals. The average crystallite size (D) was in the order of 10th of nm as computed by Scherrer method, with ternary phase seemingly affect the straightforward influence of glycine fuel concentration on the final crystallite sizes. UV-Vis analysis indicates two optical energy bandgaps which increased as glycine concentration increase. The antibacterial test against Staphylococcus aureus and Escherichia coli bacteria revealed comparable activity to that of Azithromycin standard drug, which increased with glycine concentration increase. The glycine-based tailored structural, optical, and biological properties of such trimetallic NCs making them of considerable candidate for certain applications development, possibly electronics and antibiotics; a case that encourage further investigations.

Effect of TiO2 on crystallization and mechanical properties of MgO–Al2O3–SiO2 glasses containing P2O5

MgO–Al2O3–SiO2 glass-ceramics have been widely used in military, industrial, and construction applications. The nucleating agent is one of the most important factors in the production of glass-ceramics as it can control the crystallization temperature or the grain size. In this study, we investigated the effect of replacing P2O5 with different amounts of TiO2 on the crystallization, structure, and mechanical properties of an MgO–Al2O3–SiO2 system. The crystallization and microstructure were investigated by differential scanning calorimetry, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The mechanical properties were investigated by measuring the Vickers hardness, Young's modulus, and fracture toughness. The results showed that adding TiO2 favored the precipitation of fine grains and significantly increased the Vickers hardness, Young's modulus, and fracture toughness of the glasses. Introducing an appropriate amount of TiO2 can make a glass structure more compact, promote crystallization, and improve the mechanical properties of MgO–Al2O3–SiO2 glass-ceramics.

Chemical Mechanical Polishing of MgO Substrate and Its Effect on Fabrication of Atomic Step-Terrace Structures on MgO Surface by Subsequent High-Temperature Annealing

Single-crystalline MgO is used as a substrate for the deposition of various functional thin films. The present study focused on the development of a complete sequence of fabricating atomic step-terrace structures on the MgO substrate via a method that includes grinding, precise mechanical polishing, chemical mechanical polishing (CMP), and high-temperature annealing. The effect of a damage-free surface pretreatment on the subsequent high-temperature annealing was investigated. An atomically smooth and damage-free MgO substrate surface with an average surface roughness of 0.05 nm was obtained via a CMP process using a colloidal silica slurry. Atomic step-terrace structures were formed on the substrate after the high-temperature annealing process at 1000 °C for 20 h under atmospheric air. The obtained step height was 0.20 nm, which corresponds to one-half the unit cell of an MgO crystal (0.21 nm). By contrast, when a mechanically damaged MgO substrate was subjected to the annealing process, Ca segregation was observed on the annealed surface, without the formation of an atomic step-terrace structure. CMP was found to be necessary prior to high-temperature annealing to attain atomic step-terrace structures and to avoid the out-diffusion of impurities in the MgO bulk crystals.

Convergence of Electronic Structure Properties in Ionic Oxides Within a Fragment Approach

Embedded-cluster models of crystalline solids are important to allow accurate wave function methods to be applicable to solids. The ab-initio model potential method, in which the crystal is divided into three different fragments, one quantum fragment, one ab-initio model potential fragment and one point-charge fragment, has historically been shown to be a viable tool for describing the electronic structure in ionic solids. The optimal size of these regions is, of course, individual for each crystal. In this study we analyzed the convergence of the electronic structure properties with respect to an increase of the size of the quantum part and the layer of potentials. MgO crystal and Ni: MgO were used for this purpose as examples of an ideal crystal and a crystal with a point defect. We demonstrated that with an increase of the cluster size, the electron density in the inner part of the cluster becomes very similar to the electron density in the periodic model. Clusters, embedded into a layer of model potential and electrostatic field, are a good alternative to periodic description.

Synthesis, characterization, visualization, and growth mechanism of macro-sized tubular MgO crystals formed in situ from refractory magnesia with aluminum

MgO crystals are widely used in many industries for resisting thermal and corrosion resistance. Macro-sized tubular MgO crystals with porous structures were successfully synthesized via the compaction of magnesia and aluminum powder at temperatures above 1400 °C in an air atmosphere. The morphology and densification of the MgO tube could be easily controlled by the shape of the bore on the Al2O3 lid and the heat treatment temperature. The bore of the Al2O3 crucible was critical for MgO tube growth. The thermite reaction produced a large amount of Mg vapor, and the oxygen in the crucible was squeezed out through the bore. Owing to the constraint of the air atmosphere, the MgO vapor flowing out of the crucible, which is generated by the oxidation of the Mg vapor, is preferentially deposited around the bore to form a MgO wall. Macro-sized tubular MgO crystals were obtained by MgO wall growth. A high-temperature visualization system based on monochromatic light was applied to observe the MgO tube growth process, and the growth mechanism was confirmed. These findings can be expected to enhance the aluminum-containing magnesia-based refractories with self-healing and presents a promising strategy for the economical production of high-purity MgO.

All-optical reconstruction of three-band transition dipole moments by the crystal harmonic spectrum from a two-color laser pulse.

When a bulk solid is irradiated by an intense laser pulse, transition dipole moments (TDMs) between different energy bands have an important influence on the ultra-fast dynamic process. In this paper, we propose a new all-optical method to reconstruct the k-dependent TDMs between multi-bands using a crystal high-order harmonic generation (HHG). Taking advantage of an obvious separation of bandgaps between three energy bands of an MgO crystal along the <001 > direction, a continuous harmonic spectrum with two plateaus can be generated by a two-color laser pulse. Furthermore, the first harmonic platform is mainly dominated by the polarization between the first conduction band and the valence band, and the second one is largely attributed to the interband HHG from the second conduction band and the valence band. Therefore, the harmonic spectrum from a single quantum trajectory can be adopted to map TDMs between the first, second conduction bands, and the valence one. Our work is of great significance for understanding the instantaneous properties of solid materials in the strong laser field, and will strongly promote the development of the HHG detection technology.

Formation and crystal growth of needle-like rutile in glass- ceramics

Glass-ceramic, which has negligible dielectric loss, high mechanical strength, excellent drop resistance, low CTE, and low density for lightweight design, is the best option for the back cover of mobile devices in the 5 G era. Herein, the effect of P2O5 on the phase separation and crystallization of MgO–Al2O3–SiO2-TiO2 glass-ceramics is studied. The incorporation of P2O5 in the glass structure leads to phase separation, in which the P and Mg-enriched phase was formed in the glass matrix, and promotes the increase of Tg. With the increase of P2O5 content, the precipitated crystals change significantly. First, the silicate crystals (Mg2SiO4) disappear, whereas the phosphate crystals (LiMgPO4) emerge when 2 mol% P2O5 is introduced. Second, titanate crystal (MgTi2O5) can not be observed when 4 mol% P2O5 is introduced. The Ti5O9 crystals appear simultaneously with LiMgPO4 crystals and transform to rutile TiO2 crystals at high temperature. Interestingly, the needle-like rutile TiO2 crystals, which is 300 nm long and 20 nm wide, have been found in a glass with 4 mol% P2O5. The large L/D ratio of needle-like crystals increases the hardness significantly from 6.08 GPa to 7.14 GPa. Similar to other fiber reinforced composites, this needle-like crystals provide a new strategy to improve the mechanical properties of glass ceramics.

Many-body effects for the Mg 2s XPS of MgO

The energy separation of the higher lying cation XPS binding energies, BEs, for MgO is examined. It is shown that the Hartree–Fock BEs overestimate the separation of the Mg BE(2s) and BE(2p), because an important many-body effect is neglected in the determination of the Hartree–Fock BEs. Once the many-body effect is taken into account, there is good agreement between theory and the XPS measurement. The character of this atomic many-body effect is established in terms of a nearly degenerate configuration that is needed to describe the wavefunction when an Mg 2s electron is ionized. The results provide additional evidence of the ionic character of the MgO crystal. Given the atomic character of the many-body effect, it is likely to apply also to the BE separations of other closed shell oxides.

Reactive RF magnetron sputtering epitaxy of NiO thin films on (0001) sapphire and (100) MgO substrates

Epitaxial growths of NiO thin films were realized on (0001) sapphire and (100) MgO substrates by using a reactive RF magnetron sputtering method. The NiO epilayers grown on a (0001) sapphire exhibited the (111)-oriented double-domain structure, which comprised of a triangular and its inverted triangular grains. Meanwhile, the NiO epilayers on a (100) MgO exhibited the (100)-oriented single-domain structure, which comprised of quadrangular grains. The observed grain structures most likely reflect the growth planes of respective NiO epilayers, and, mixed crystals of NiO and MgO were present near the interface. Therefore, a (100) MgO substrate is suitable for obtaining a single-domain NiO epilayer, whereas a (0001) sapphire substrate is suitable for obtaining a NiO epilayer without interdiffusion between NiO and sapphire. These NiO epilayers will be expected for applying the physical properties evaluation using photoluminescence or Hall measurements, and the fabrication of electrical or optical devices.

Antibacterial activity of V- doped rod-like MgO crystals decorated with nanoflake layer

In present study, we report a V doping fabrication method for obtaining rod-like MgO crystals decorated with a nanoflake layer. This novel structure has only been minimally reported in literature. Pure MgO and Mg2V2O7–MgO composite materials were obtained by precipitation and impregnation methods, with vanadium added concentrations of 0–9%. The influence of V doping on crystal structure and particle morphology of MgO was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis demonstrated that MgO has a cubic structure, while X-ray photoelectron spectroscopy (XPS) revealed that V5+ exists on the surface of MgO. The specific surface areas and pore sizes of MgO composites were calculated by BET and BJH analysis. These techniques revealed that specific surface area and pore size of MgO increased due to vanadium doping. The antibacterial effects of Mg2V2O7–MgO composite materials against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were assessed using a bacterial killing/colony-forming unit (CFU) assay and bacteriostatic ring method. Our results demonstrate that V doping dramatically improved antimicrobial properties of MgO, with 7 mol% doping inducing the best antibacterial activity. The antibacterial mechanisms of Mg2V2O7–MgO composite material were also proposed.

Studies on the Temperature Dependences of Spin-Hamiltonian Parameters for Some 3dn Ions in Mgo Crystal from a Complete Equation

Studies on the Temperature Dependences of Spin-Hamiltonian Parameters for Some 3dn Ions in Mgo Crystal from a Complete Equation

Self-Organized Quantum Dots from a Material with Colossal Magnetoresistance (La0.7Ca0.3MnO3), Grown on MgO Crystals

Self-Organized Quantum Dots from a Material with Colossal Magnetoresistance (La0.7Ca0.3MnO3), Grown on MgO Crystals

Magnesite-derived MgO promoted with molten salts and limestone as highly-efficient CO2 sorbent

This study evaluated the CO2 capture performance of MgO obtained from mineral magnesite and doped with limestone and molten Li, Na and K nitrates under consecutive sorption/desorption cycles via thermogravimetric analysis. Increasing the molten promoter loading resulted in a higher CO2 sorption rate, while elevated CaCO3 amounts impeded CO2 diffusion. When exposed to a 30 % CO2 flow at 300 °C for 30 min, the sorbent with alkali salts and CaCO3 to MgO molar ratios of 0.20 and 0.05 respectively attained a capture of 7.2 mol CO2/kg of sorbent and a negligible activity loss (∼6%) after 50 cycles. This performance was promising, considering the mineral nature of precursors. In-situ X-ray diffraction revealed the growth of the MgO crystal after each desorption, proving the gradual MgO sintering. However, the morphological transformations occurring during cyclic operation and especially if high conversions of MgO are reached, trigger an alkali salt redistribution that grants high stability.

Study of Elastic Properties of Ionic Solids at High Temperature and Volume Expansion Ratio

In our study we develop a new expression for temperature dependence of thermal pressure for MgO and CaO crystal. A generally elastic property of solid depends on the strength of inter atomic forces of solid. So far our work has been resolute on thermal pressure is dependent of temperature and diverges it’s linearly in high temperature volume expansion ratio through the effect of temperature. This present method has been developed on the temperature dependence of thermal pressure for MgO and CaO crystal at atmospheric pressure and volume expansion ratio at high temperature. A neighboring data of Gruneisen parameter is found to be in close convention with theoretical and investigational confirmations the standing of present study.

Compensation of laser propagation effects within solids for high harmonic generation of extreme ultraviolet radiation

High harmonic generation (HHG) from solids offers a convenient means of producing coherent extreme ultraviolet (EUV) radiation. However, the achievable harmonic yield is greatly affected by propagation effects that the driving laser pulse experiences with spatiotemporal distortion when passing through solids. Here, we intend to optimize EUV harmonics generated from crystals by pre-shaping the driving laser pulse via spectral phase modulation through a genetic algorithm. Our experimental results obtained from MgO, sapphire and quartz crystals demonstrate EUV yield improvements, without increasing the incident laser fluence, up to an order of magnitude along with cut-off extension and selective harmonic enhancement. As a practical tool of compensating laser propagation effects, our method is expected to facilitate solid-based HHG applications such as high-energy photon spectroscopy and multi-petahertz signal processing.

The Calcium Looping process for energy storage: Insights from in situ XRD analysis

This work reports a novel in situ XRD analysis on the multicycle calcination/carbonation of natural limestone and dolomite at relevant conditions for thermochemical energy storage (TCES) in concentrated solar power (CSP) plants. The experiments allow analysing noninvasively the time evolution of the different phases involved in the Calcium Looping (CaL) process. Our work has revealed new key features to understand the progressive loss of multicyclic carbonation reactivity of the CaO derived from calcination. The CaCO3 structure formed in the first step of dolomite decomposition has smaller unit cell volume than the CaCO3 naturally present in limestone. The CaO that stems from decomposition of the CaCO3 derived from dolomite first decomposition shows a greater carbonation reactivity compared to the CaO derived from limestone. The smaller size of the CaO nascent crystals and their relatively higher reactivity for dolomite compared to limestone is related to the presence of inert MgO crystals, which prevent CaO sintering and crystallite growth. However, the size of the MgO crystals derived from dolomite decomposition increases monotonically with time, which progressively hampers their hindrance effect. Our work also shows a positive correlation between the growth of the CaO crystallite size and the decline of preferred orientation in the CaO (100) plane as the number of cycles is increased and CaO loses reactivity. The observed evolution with the cycles of CaO crystallite size and reactivity can be attributed to the incompletion of carbonation. The unreacted CaO that remains in the calcination step suffers severe sintering which hinders its reactivity. Thus, the fraction of fresh, reactive CaO derived from CaCO3 decomposition that nucleates on the old and less reactive CaO declines progressively with the cycles.

Measurements of Energy Loss of Charded Particles Travelling in Crystalline Materials along the Channeling Directon

A method for determining the energy loss and mean dechanneling distance of light charged particles traveling along a low index axis of a crystal in the backscattering geometry, is presented. The method is based on nuclear resonance reactions which act as a marker for the range in the backscattering spectra. Computer simulations based on the assumption of an exponential rate of dechanneling of the incoming particles in the crystalline material, are in good agreement with measured spectra. The results of applying this method to protons and alphas in crystals of Si, SiO2, SiC and MgO are discussed and possible improvements are indicated.

MgO intercalation and crystallization between epitaxial graphene and Ru(0001)

MgO intercalation and crystallization between epitaxial graphene and Ru(0001)