MgO Crystals Research Articles

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

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

Generation of structured coherent extreme ultraviolet beams from an MgO crystal.

Short wavelength high-harmonic sources are undergoing intense development for applications in spectroscopy and microscopy. Despite recent progress in peak and average power, spatial control over coherent extreme ultraviolet (XUV) beams remains a formidable challenge due to the lack of suitable optical elements for beam shaping and control. Here we demonstrate a robust and precise approach that structures XUV high-order harmonics in space as they are emitted from a nanostructured MgO crystal. Our demonstration paves the way for bridging the numerous applications of shaped light beams from the visible to the short wavelengths, with potential uses for applications in microscopy and nanoscale machining.

Study on the Synthesis and Structural Properties of Zeolite A-MgO Composite for Defluoridation of Water

Zeolite A-MgO composite was synthesized in presence of zeolite A particles, MgCl2 and urea solution under hydrothermal reaction at 150oC for 5 h followed by calcination at 600°C/2 h. XRD and FTIR results showed the crystallization of MgO along with NaA zeolite crystals. Nano-sheet like MgO particles (50-70 nm) were grown onto the surface of NaA zeolite crystals (1 μm). BET surface area and pore size of the sample were found to be 69 m2.g−1 and 3.9 nm, respectively. XPS analysis showed the binding energies of O1s, Si2p, Na1s, Al2p and Mg2p as 531.6, 102.4, 1072.2, 74.2 and 49.9 eV, respectively. The synthesized product (1 g.L−1 dose) showed 72% adsorption of fluoride (7.24 mg.L−1) within 5 min and reached up to 94% for 90 min at pH 6.8. The adsorption capacity of the sample was calculated as 107.64 mg.g−1 from Langmuir isotherm. The sample could be regenerated up to 5th cycle. A tentative mechanism for the adsorption of fluoride from aqueous solution by the synthesized zeolite A-MgO composite was proposed.

Intermixing induced anisotropy variations in CoB-based chiral multilayer films

We examine the atomic intermixing phenomenon in three distinct amorphous CoB-based multilayer thin film platforms — Pt/CoB/Ir, Ir/CoB/Pt and Pt/CoB/MgO — which are shown to stabilise room-temperature chiral magnetic textures. Intermixing occurs predominantly between adjacent metallic layers. Notably, it is stack-order dependent, and particularly extensive when Ir sits atop CoB. Intermixing induced variations in magnetic properties are ascribed to the formation of magnetic dead layer arising from CoIr alloying in the metallic stacks. It also produces systematic variations in saturation magnetization, by as much as 30%, across stacks. Crucially, the resulting crossover CoB thickness for the transition from perpendicular to in-plane magnetic anisotropy differs by more than 2 across the stacks. Finally, with thermal annealing treatment over moderate temperatures of 150–300 °C, the magnetic anisotropy increases monotonically across all stacks, coupled with discernibly larger H c for the metallic stacks. These are attributed to thermally induced CoPt alloying and MgO crystallization in the metallic and oxide stacks, respectively. Remarkably, the CoB in the Pt/CoB/MgO stacks retains its amorphous nature after annealing. Our results set the stage for harnessing the collective attributes of amorphous CoB-based material platforms and associated annealing processes for modulating magnetic interactions, enabling the tuning of chiral magnetic texture properties in ambient conditions.

Dynamic Core Polarization in High Harmonic Generation from Solids: The Example of MgO Crystals.

Previously, the strong field processes in solids have always been explained by the single-active-electron (SAE) model with a frozen core excluding the fluctuation of background electrons. In this work, we demonstrate the strong field induced dynamic core polarization effect and propose a model for revealing its role in high harmonic generation (HHG) from solids. We show that the polarized core induces an additional polarization current beyond the SAE model based on the frozen cores. It gives a new mechanism for HHG and leads to new anisotropic structures, which are experimentally observed with MgO. Our experiments indicate that the influences of dynamic core polarization on HHG are obvious for both linearly and elliptically polarized laser fields. Our work establishes the bridge between the HHG and the dynamic changes of the effective many-electron interaction in solids, which paves the way to probe the ultrafast electron dynamics.

High-Index (Ni,Mg)O Crystallization during Molten Salt Synthesis

Heterogeneous NiO–MgO materials and (Ni,Mg)O solid solutions have found application in catalysis owing to the combined redox properties of NiO and basic properties of MgO. Examples include the use of (Ni,Mg)O to tune the surface reducibility of Ni(II), which determines the Ni cluster size and the tendency of catalysts to form coke and deactivate in dry reforming and partial oxidation of methane. To this end, control of the metal oxide structure and surface properties, both in terms of composition and faceting, are of paramount importance. In this article, we show that both compositional and morphological control can be achieved by selecting an appropriate molten salt synthesis (MSS) to obtain a solid solution of (Ni,Mg)O or segregated NiO–MgO crystals at low temperature (≤550 °C). Our findings reveal that nitrate precursors in a medium with excess NaCl/KCl (1:1) putatively results in the formation of a reaction intermediate comprised of molten K3Na(Mg,Ni)Cl6. In the presence of exchanged nitrate ions acting as Lux-Flood bases, this molten intermediate forms solid oxide solutions whose morphology is dictated by the composition of the medium, shifting from an octahedral to icositetrahedral (trapezohedral) habit with increasing Ni(II) content. Conversely, when using NaNO3/KNO3 (1:1) as a growth medium, solid solutions are inhibited and we observe segregation of the oxide phases. Under these conditions, the morphologies of the heterogeneous products are predominantly octahedral for MgO and truncated cubic-to-octahedral for NiO, depending on the Ni(II) content. Systematic examination of Ni/Mg mixed metal oxide crystallization highlights the strikingly different pathways followed in nitrate and chloride salt media. Overall, this study highlights the importance of molten intermediates in solid solution synthesis and reveals that the judicious selection of ions in MSS plays a major role in achieving well-defined crystals with high-index facets.

Glass crystallization making red phosphor for high-power warm white lighting

Rapid development of solid-state lighting technology requires new materials with highly efficient and stable luminescence, and especially relies on blue light pumped red phosphors for improved light quality. Herein, we discovered an unprecedented red-emitting Mg2Al4Si5O18:Eu2+ composite phosphor (λex = 450 nm, λem = 620 nm) via the crystallization of MgO–Al2O3–SiO2 aluminosilicate glass. Combined experimental measurement and first-principles calculations verify that Eu2+ dopants insert at the vacant channel of Mg2Al4Si5O18 crystal with six-fold coordination responsible for the peculiar red emission. Importantly, the resulting phosphor exhibits high internal/external quantum efficiency of 94.5/70.6%, and stable emission against thermal quenching, which reaches industry production. The maximum luminous flux and luminous efficiency of the constructed laser driven red emitting device reaches as high as 274 lm and 54 lm W−1, respectively. The combinations of extraordinary optical properties coupled with economically favorable and innovative preparation method indicate, that the Mg2Al4Si5O18:Eu2+ composite phosphor will provide a significant step towards the development of high-power solid-state lighting.

A periodic equation-of-motion coupled-cluster implementation applied to F-centers in alkaline earth oxides.

We present an implementation of the equation of motion coupled-cluster singles and doubles (EOM-CCSD) theory using periodic boundary conditions and a plane wave basis set. Our implementation of EOM-CCSD theory is applied to study F-centers in alkaline earth oxides employing a periodic supercell approach. The convergence of the calculated electronic excitation energies for neutral color centers in MgO, CaO, and SrO crystals with respect to the orbital basis set and system size is explored. We discuss extrapolation techniques that approximate excitation energies in the complete basis set limit and reduce finite size errors. Our findings demonstrate that EOM-CCSD theory can predict optical absorption energies of F-centers in good agreement with experiment. Furthermore, we discuss calculated emission energies corresponding to the decay from triplet to singlet states responsible for the photoluminescence properties. Our findings are compared to experimental and theoretical results available in the literature.

Effects of BaO on crystallization, structure and dielectric properties of MgO–Al2O3–SiO2 glass–ceramics for LTCC applications

Cordierite-based glass–ceramics for LTCC applications were prepared by traditional sintering method. And the effects of BaO addition on the crystallization, structure and dielectric properties were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffractometer (XRD), dilatometer and impedance instrument. The DSC curves displayed that the glass transition temperature (Tg) slowly decreased with the BaO content increasing from 0 to 4 mol%. However, the onset of crystallization temperature (Tx) and crystallization peak temperature (Tc) showed the opposite trend. XRD analysis revealed that μ-cordierite was the major crystal phase for all the glass–ceramic samples, while α-cordierite precipitated as the minor crystal phase with BaO addition. As more BaO was added, the bulk density gradually increased, while the porosity decreased, indicating that BaO improved the sinterability of the glass samples. The dielectric constant showed minimum value with the addition of 2 mol% BaO, and the dielectric loss reached the minimum value when the content of BaO was 3 mol%. Wherein, after heated at 950 °C, glass–ceramics doped with 2 mol% BaO showed a dense structure, a relatively low dielectric constant (4.53), a low dielectric loss (2 × 10−3) at 1 MHz, and a proper CTE value (3.74 × 10–6/°C), which can be used to prepare LTCC materials.

Investigation of factors affecting on the efficiency of second harmonic ‎generation of the continuous-wave focused Gaussian beam of 1064 nm inside the ‎periodically poled nonlinear crystals

In this research, the nonlinear propagation equations of the fundamental and second harmonic waves coupled to the heat equation are solved for a focused Guassian beam inside two quasi-phase matched periodically poled MgO: PPLN and MgO: PPLT crystals, and the optimum focal length and radius of the continuous-wave laser beam with the wavelength of 1064 nm and with Gaussian profile, and also, the optimal phase-mismached parameter are calculated and the dependence of the second harmonic efficiency on these parameters is shown. Also, the effects of the thermal distribution inside the crystal on the second harmonic generation efficiency are investigated and it is shown how the thermal distribution reduces the second harmonic efficiency and, accordingly, the optimal crystal length for different incident powers is determined and shown that the lower crystal lengths should be selected for higher incident powers. Finally, a comparison between the second harmonic efficiencies in two crystals of MgO: PPLN and MgO: PPLT is performed considering the thermal distribution for different insident powers and it is shown that for the lower/ higher incident power than 21 watts, the crystal of MgO: PPLN / MgO: PPLT is more suitable and more efficient for second harmonic generation.

Metal chloride-loaded biochar for phosphorus recovery: Noteworthy roles of inherent minerals in precursor

Phosphorus (P) is a valuable resource, while it is vastly lost with wastewater causing eutrophication. In this study, to recover P, composite biochars were prepared by pyrolyzing biowaste impregnated with FeCl3 or MgCl2. It was found that inherent mineral profiles in the biowastes played important roles in interacting with metal chlorides and determined P sorption and precipitation. Specifically, two biowastes containing distinct mineral contents, sawdust and sediment, were selected as model components, being alone or mixed at 1:1 (w/w) to prepare biochars with low, moderate and high mineral contents. Results showed that biochar itself could not absorb P, while loading FeCl3 or MgCl2 achieved P recovery rates of approximate 60–100% and 50–100%, respectively, via electrostatic attraction or ligand exchange of PO43− with –OH/-COOH, which was attributed to the enhanced positive charges and –OH/-COOH on the materials by these metal chlorides. Inherent minerals inhibited FeCl3 transforming into Fe3O4 in pyrolysis and promoted generation of Fe4(PO4)3(OH)3 in P sorption, thus high-mineral content was more appropriate for FeCl3 loading; however, precursors with low-mineral content was suitable for MgCl2 loading, since the bulk-C in biochar acted as porous structure to support MgO crystals with high superficial area (∼255.85 m2 g−1). Besides, FeCl3 and MgCl2 both drove dissolution of inherent minerals significantly, while inherent minerals inhibited release of soluble Fe and Mg2+ into solution, which minimized secondary pollution. This study implied that in constructing composite biochar for catching P, the type of metal chloride should match the inherent minerals in biowastes to maximize P recovery and minimize secondary pollution.

Generation of tunable ultraviolet femtosecond pulse in MgO crystal by cascaded four wave mixing

Ultraviolet femtosecond laser pulse is an important tool in studying ultrafast chemical and physical processes. Realizing broadband ultraviolet laser pluses with a wide tunable range would significantly facilitate the study of ultrafast processes. As an effective and convenient method, the cascaded four-wave mixing (CFWM) has been widely adopted to generate broadband and tunable ultraviolet femtosecond laser pulses. In this work, we carry out CFWM in MgO crystal by using two 400-nm pulses to generate tunable ultraviolet femtosecond pulse. The MgO crystal is chosen due to its high third-order nonlinear susceptibility, large band gap and high transmittance in the ultraviolet region. In the experiment, nine frequency up-converted and five frequency down-converted sidebands are observed. The measured wavelength and scattering angle of each sideband are consistent with the CFWM theory predictions. The wavelength range of the sidebands covers 350–450 nm. The total conversion efficiency of the ultraviolet sidebands is 1.2%, which is higher than the reported values with visible/near infrared driven lasers. Meanwhile, the spectra of the high-order sidebands present a Gaussian profile and can support a Fourier-transform-limited pulse duration of less than 50 fs. Besides, the central wavelengths of the sidebands can be effectively tuned by adjusting the time-delay between the two pre-chirped pump pulses. Our study provides an efficient and convenient scheme to generate short ultraviolet femtosecond pulses with a wide tunable range.

Enhancement of the Congo Red Adsorption Capacity of Biochars by Surface Modification with MgCl2 Pretreatment

Objectives : The physicochemical characteristics of Mg-biochar composites derived from kelp and pine after pretreatment with MgCl2 were analyzed, and their adsorption capacities for an anionic dye, Congo red (CR), were evaluated.Methods : After pretreating 60 g of kelp and pine sawdust in 1 L of 0.1 M MgCl2･6H2O, the raw materials were pyrolyzed at 500℃ to produce Mg-biochar composites (kelp based KB-Mg and pine based PB-Mg). The fundamental physicochemical characteristics of the Mg-biochar composites were examined, and their adsorption capacities for CR were investigated using different initial pH values, adsorption kinetic models, and adsorption isotherm models.Results and discussion : The Mg-biochar composites showed the development of uniform deposits of Mg minerals primarily as MgO crystal on the surface by the surface modification with MgCl2. When the pristine biochars were surface-modified with MgCl2, their adsorption capacities for CR were significantly increased over the entire pH range tested. The CR adsorption process by all biochars was best described with the pseudo-first order kinetics model, and the adsorption isotherm characteristics were better described with the Langmuir isotherm model for all biochars. The Langmuir maximum adsorption capacities for KB-Mg and PB-Mg were 423.0 mg/g and 394.7 mg/g, respectively. It is suggested that the main mechanism for CR adsorption on the Mg-biochars is electrostatic attraction between CR and the biochars.Conclusions : The results showed that surface modification with MgCl2 could greatly enhance the CR adsorption capacity of biochars, and the results demonstrated the great potential of KB-Mg and PB-Mg for CR removal.

Multianalyte Mg-Doped InGaZnO Electrolyte-Insulator-Semiconductor Biosensors and Multiple Material Characterizations of Membrane Nanostructures

Mg-doped InGaZnO (IGZO) electrolyte-insulator-semiconductor (EIS) biosensors were fabricated with multianalyte sensing capability. H+, Na+, and K+ ion sensing behaviors were examined and urea, glucose, and creatine detection through enzymatic reaction was performed. Results indicate that Mg doping IGZO membranes with appropriate annealing had better multi-sensing performance than that of regular membranes. Moreover, multiple material characterizations of membrane nanostructures, including of atomic force microscopy (AFM) surface morphology evaluation, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were conducted. Material crystalline and chemical binding properties were also performed, including energy dispersive X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDX), and photoluminescence (PL). These detailed studies indicate that the incorporation of Mg in the membrane can form MgO crystals to enhance compactness, crystallization and grainization, which can reinforce the surface sites on the membrane. Mg-doped IGZO EIS multianalyte biosensors show promise for future portable and wearable biosensing applications.

Morphological changes and their thermal conductivities of MgO crystals containing various impurities (B, Ca, Si)

AbstractMgO is industrially produced from seawater or dolomite as the raw material. MgO synthesized from seawater has a relatively low impurity concentration. However, these impurities strongly affect the fine structure and physical properties (especially the thermal conductivity) of MgO. In this research, the influence of impurity concentration on the MgO grain growth and its thermal conductivity was investigated. The processing conditions for MgO powder synthesis were optimized by a polymer complex method using magnesium nitrate hydrate, citric acid, ethylene diamine, and chemical compounds containing B, Ca, or Si, which are the main impurities of MgO produced from seawater. The morphology and phase composition of the MgO powders were investigated by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and energy dispersive X‐ray spectroscopy (EDS). The morphological changes and differences in the thermal conductivity of MgO crystalline systems containing impurities (B, Ca, and/or Si) were clarified, and the relationship between the fine structure of MgO crystals containing impurities and their thermal conductivities was described in detail.

The Sensitivity of Dislocation Rosettes to the Shape of a Berkovich Indenter on LiF and MgO Crystals

The peculiar effect observed under the indentation of the (001) plane of LiF and MgO single crystals, namely, the sensitivity of the form of dislocation rosettes to the shape of the indenter, is considered. It is shown that the dislocation rosettes being formed around Vickers indentations are symmetrical, while the rosettes around Berkovich indentations are asymmetrical, the edge arms of the dislocation rosettes are different with respect to their length, and the screw arms do not demonstrate such asymmetry. Also, an orientational effect is found under the penetration of a Berkovich indenter, thus, the form of the dislocation rosettes and length of the edge arms change at varying the orientation of the indenter relative to the crystallographic directions of the sample. It is also shown that the asymmetry of the dislocation rosettes is more pronounced on harder crystals and increases with the growth in the load on the indenter. The factors responsible for the anomaly in the development of the dislocation rosettes under nano- and microindentation of the (001) plane of cubic crystals by a Berkovich indenter are found.

Structurally improved MgO adsorbents derived from magnesium oxalate precursor for enhanced CO2 capture

Facile, green and solvent-free fabrication of efficient MgO-based adsorbents is highly necessary for their intermediate-temperature CO2 capture applications. In this work, MgO adsorbents were prepared by calcining magnesium oxalate precursor under different calcination atmospheres and temperatures. N2 adsorption-desorption, X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and CO2 temperature programmed desorption were employed to study their physicochemical properties. CO2 adsorption performance was evaluated by testing the adsorbents in a dry stream containing 10%CO2 at a mild temperature of 200 °C. The influence of calcination conditions on their structure-performance relationships was investigated. Calcination atmosphere and temperature will significantly affect the microstructure and CO2 adsorption performance. Calcination in a flowing CO2 stream will endow the adsorbent with minimized MgO crystal size, and this will offer more O2− active sites at the edges and corners for enhanced CO2 adsorption capacity. The precursor can hardly be completely decomposed at a lower calcination temperature to form porous structure, and the basic active sites available for CO2 adsorption are limited. A higher calcination temperature will result in sintering of MgO crystals, pore structure blockage and loss of the O2− basic active sites, and CO2 adsorption capacity will therefore be reduced. The desired MgO-C-500 adsorbent calcined in a flowing CO2 stream at 500 °C exhibits the highest CO2 adsorption capacity of 5.09 mmol CO2/g. The results will pave the way for developing highly efficient MgO adsorbents for separating CO2 from industrial exhaust gas.

About complexity of the 2.16-eV absorption band in MgO crystals irradiated with swift Xe ions

The precise study of the accumulation and subsequent thermal annealing of the defects responsible for the complex absorption band around 2.16 eV, being under discussion in the literature for a long time, has been performed in highly pure MgO single crystals exposed to 0.23-GeV 132Xe ions with a fluence of Φ = 5 × 1011 − 3.3 × 1014 ions/cm2. Three Gaussian components with the maxima at 2.16, 2.02 and 2.40 eV have been considered as a measure of so-called D1, D2 and D3 defects. Similar to the F and F+ centers, the concentration of these defects increases at high fluences without saturation marks, thus confirming their radiation-induced nature (involvement of novel Frenkel defects). The accumulation of D1 and the first stage of D-type defect annealing up to 700 K occurs similarly to single F-type centers, while the following increasing stage for D2,3 starts above 700 K; their concentration reaches the maximum at 900 K (practically plateau is seen in this temperature region for D1) and complete annealing of the D-type defects proceeds at 1100 K. Behavior of the D1 defects (accumulation rate, annealing kinetic at high temperatures) clearly differs from that for other D-type defects (especially D2). In our opinion, the D1 defects are high-order aggregates of anion vacancies (and not the anion vacancy dimers), while the involvement of additional structural defects into the D2,3 defects is suggested.

Effect of interband polarization on a solid's high-order-harmonic generation just belowthe band gap.

A series of theoretical and experimental results has proved that harmonics below/above the band gap are produced mainly by the intraband current/interband polarization for solids in strong mid-infrared laser pulses. However, which mechanism dominates the harmonic process is still debated. In this work, based on simulating high-order-harmonic generation from an MgO crystal in a linearly polarized mid-infrared laser by solving semiconductor Bloch equations, we demonstrate that harmonics just below the band gap originate from the interference between intraband and interband currents. Furthermore, it is found that intensities of harmonics just below the band gap are apparently enhanced with an increase in the incident laser's strength. By analyzing the band dispersion and the transition dipole moment of the 001-cut MgO crystal, this can be attributed to the interband polarization between two conduction bands.

Quantum path interferences and selection in interband solid high-order harmonic generation in MgO crystals

We theoretically investigate the quantum path interferences in interband transitions in solid high-order harmonic generation. The field strength scaling of the 19th harmonic yield from MgO crystal driven by 1600-nm lasers exhibits a sharp minimum. By solving the semiconductor Bloch equation, we separate the short and long trajectories. Our numerical calculation shows that this minimum originates from the coherent interferences between the short and long trajectories. We also illustrate that the interference minimum depends sensitively on the band dispersion, which can be used to retrieve the band structure accurately. We further report that the two-color fields can select the short or long quantum path effectively by controlling the phase. The yield at the plateau or cutoff region of the harmonic spectra can be enhanced by around one order of magnitude by adding a third harmonic with an intensity of only $10%$ of the fundamental field. Moreover, an isolated attosecond pulse (IAP) is synthesized by controlling the harmonic trajectories in the two-color scheme. The yield of this IAP is enhanced by one order of magnitude compared with the IAP generated by the single-color scheme.