Calcium Atoms Research Articles

Quantum entanglement of optical photons: the first experiment, 1964–67

The first experimental observation of entangled visible light was achieved by optically exciting free atoms of calcium and detecting pairs of photons emitted in a two-stage cascade. The polarizations of the entangled photons were observed to be correlated, in agreement with quantum theory. This review describes the rationale, methodology, challenges, and results, including experimental details not previously published.

CaRu2Zn10, SrRu2Zn10 and EuRu2Zn10 – new superstructure variants of ThMn12

Abstract The zinc-rich intermetallic phases CaRu2Zn10, SrRu2Zn10 and EuRu2Zn10 were synthesized by induction-melting of the elements in sealed tantalum ampoules followed by annealing to increase the crystallinity. The samples were characterized by powder X-ray diffraction and the structures were refined from single crystal X-ray diffractometer data: new type, P42/nnm, a = 894.68(14), c = 518.44(9) pm, wR2 = 0.0830, 432 F 2 values, 22 variables for CaRu2Zn10, a = 907.01(10), c = 516.35(6), wR2 = 0.0469, 445 F 2 values, 22 variables for SrRu2Zn10 and a = 902.84(9), c = 515.91(5) pm, wR2 = 0.0469, 434 F 2 values, 22 variables for EuRu2Zn10. The three structures are new ordering variants of the aristotype ThMn12. They are discussed on the basis of a group-subgroup scheme and compared to the known superstructures CaCr2Al10, ErNi10Si2 and ScFe6Ga6. The calcium atoms within the Ca@Ru4Zn16 polyhedra have flattened tetrahedral ruthenium coordination, reducing the calcium site symmetry to 4 ‾ $\bar{4}$ 2m (instead of 4/mmm in the aristotype). Electronic structure calculations show a substantial charge transfer from calcium to ruthenium and an almost neutral zinc substructure.

Shell Composition Analysis of European Flat Oyster (Ostrea edulis, Linnaeus 1758) From Marmara Sea, Türkiye: Insights Into Chemical Properties

The chemical structure of Ostrea edulis (O. edulis) shells was investigated in this work. The study determined zero charge points (PZC) of Ostrea edulis shells. The shell surface charge status is indicated by the PZC value. It was found that the shell PZC value was 8.30. The shells were subjected to Energy Dispersive X-Ray Spectroscopy (EDS) analyses and scanning electron microscope (SEM) pictures. The main structure of calcium carbonate (CaCO3) is made up of carbon, oxygen, and calcium atoms, which were found in the largest quantities based on the EDS data. The structure of CaCO3 was supported by Fourier Transform Infrared Spectroscopy (FT-IR) analysis. As part of the study, X-Ray Diffraction (XRD) investigations were conducted, and it was found that the shell structures are primarily composed of an aragonite and CaCO3 mixture. As is well known, CaCO3, which makes up roughly 94% of the shell, is the primary constituent of bivalves’ shells. This research offers a thorough examination of the chemical makeup of O. edulis shells. This study is thought to serve as the foundation for further research on the biological and chemical characteristics of marine species.

Development of a ReaxFF reactive force field for ternary phosphate-based bioactive glasses.

Phosphate-based glasses (PBGs) in the CaO-Na2O-P2O5 system have diverse applications as biomaterials due to their unique dissolution properties. A reactive force field (ReaxFF) has been developed to simulate these materials at the atomic level. The ReaxFF parameters of PBGs, including the interaction between phosphorus and calcium atoms, have been developed using a published code based on genetic algorithms. The training data, including the atomic charges, atomic forces, bond and angle parameters, and different differential energies, are chosen and measured from static quantum-mechanical calculations and abinitio molecular dynamics of PBGs. We did different short- and medium-range structural analyses on the bulk simulated PBGs with different compositions to validate the developed potential. Radial and angular distribution functions and coordination numbers of network formers and modifiers, as well as the network connectivity of the glass, are in agreement with experimental and previous simulations using both shell-model classical force fields and abinitio simulated data; for example, the coordination number of phosphorus is 4.0. This successful development of ReaxFF parameters being able to describe the bulk PBGs enables us to work on the dissolution behavior of the glasses, including the interaction of water molecules with PBGs, in future works.

Flotation Separation of Cassiterite from Calcite Using Low-Molecular-Weight Citrus Pectin as Depressant

This paper presents the development of an environmentally friendly, small molecular depressant citrus pectin for improving the recovery of cassiterite resources. Citrus pectin extracted from citrus peel was utilized as the depressant, and it demonstrated significant potential in separating calcite from cassiterite in micro-flotation tests. The molecular weight of the citrus pectin extracted in this paper decreased from 11,485,412 Da to 32,959 Da compared to commercial pectin, resulting in the depressant efficiency of the reagent. The results of a zeta potential and adsorption test indicated that citrus pectin had less and weaker adsorption on the cassiterite surface and could be replaced with NaOL. The chemical adsorption process of citrus pectin on the surface of calcite was determined through FTIR spectroscopy analysis. XPS analysis results indicated that the interaction between the carboxyl groups of citrus pectin and calcium atoms enables adsorption to occur. The AFM revealed that citrus pectin displayed a uniform and dense pattern of point-like adsorption on the surface of calcite. Micro-flotation experiments showed that cassiterite recovery of 80% can be obtained at a citrus pectin dosage of 10 mg/L. Citrus pectin has the advantages of being low-cost, highly selective, and environmentally suitable, making it a promising alternative to conventional reagents.

Steady-State Ultracold Plasma Created by Continuous Photoionization of Laser Cooled Atoms.

In this Letter we discuss our approach that makes possible creation of the steady-state ultracold plasma having various densities and temperatures by means of continuous two-step optical excitation of calcium atoms in the magneto-optical trap. A strongly coupled ultracold plasma can be used as an excellent test platform for studying many-body interactions associated with various plasma phenomena. The parameters of the plasma are studied using laser-induced fluorescence of calcium ions. The experimental results are well described by a simple theoretical model involving equilibration of the continuous source of charged particles by the hydrodynamical ion outflux and three-body recombination. The ultracold plasma with the peak ion density of 2.7×10^{6} cm^{-3} and the minimum electron temperature near 2K has been prepared. Our steady-state approach in combination with the strong magnetic confinement of the plasma will make it possible to reach extremely strong coupling in such system.

Molecular dynamics simulations of adsorption behavior of mixtures of surfactant and polymer at C3A/water and Ettringite/water interfaces

In cementitious system, surfactant is used as air-entraining agents, which is often incompatible with other chemical admixtures, such as superplasticizers. The adsorption of surfactants at solid–liquid interface is critical for the bubble stability. The measurement of adsorption properties of surfactant in fresh cement or concrete is very difficult. In this study, classical molecular dynamics simulations is used to analysis the influence of two polymers (call as HPMC and PCA, respectively) on the adsorption behaviors of the two anionic surfactants (call as HSO4 and HPO4, respectively) at the C3A/water and ettringite/water interfaces. At solid/water interface, both of HSO4 and HPO4 molecules form a monolayer with hydrophilic head groups adsorbed on the solid surfaces. After adding polymers, the adsorption conformations are changed to spherical micelle or multilayer. The electrostatic interaction between oxygen atoms of hydrophilic head groups and calcium atoms of solid surface plays a decisive role. Therefore, the value of adsorption energy of HPO4 with more negatively charged hydrophilic head groups is greater than that of HSO4. The adsorption energies of the two surfactants are weakened by the two polymers, but the adsorption energy value of HPO4 is always greater. The influence mechanism of HPMC and PCA is different. The negatively charged PCA has a strongly competitive adsorption with the surfactants. The neutral HPMC has a weak adsorption capacity but it carries many hydroxyl groups to interact with the hydrophilic head groups of surfactants.

Ca3Ru3Zn13 – a zinc-rich intermetallic phase composed of closest-packed layers

Abstract Ca3Ru3Zn13 was synthesized from the elements in a tantalum tube in a muffle furnace. The sample was annealed to 1123 K followed by slow cooling to enhance crystal growth. Ca3Ru3Zn13 was characterized through a Guinier powder pattern. The structure was refined from single crystal X-ray diffractometer data: new type, Pbcn, a = 522.92(5), b = 1792.72(14), c = 2789.6(2) pm, wR2 = 0.0590, 3451 F 2 values, 177 variables. One can describe the Ca3Ru3Zn13 structure by a stacking of closest packed layers of compositions Ca6Zn10, Ca6Zn12 and Ru6Zn15. The calcium atoms have high coordination numbers: Ca1@Zn13Ru3Ca2, Ca2@Zn15Ru4Ca, Ca3@Zn15Ru4Ca and Ca4@Zn15Ru4Ca. The shortest interatomic distances occur between the ruthenium and zinc atoms (255–273 pm). The Ru1@Zn8, Ru2@Zn10 and Ru3@Zn8 polyhedra condense via common edges to the [Ru3Zn13] substructure which hosts the calcium atoms. The zinc substructure consists of 15 crystallographically independent zinc sites with a broader range of Zn–Zn distances (255–307 pm).

Seasonal Variation in the Mesospheric Ca Layer and Ca+ Layer Simultaneously Observed over Beijing (40.41°N, 116.01°E)

In March 2020, an all-solid-state dual-wavelength narrow-band lidar system was deployed. A total of 226 nights spanning from March 2020 to July 2022 were employed in order to investigate the seasonal variations of calcium atoms and ions in the mesosphere over Beijing (40.41°N, 116.01°E). The Ca+ layer shows general annual variation, while a semiannual variation is observed on the Ca layer. The calcium atomic column densities ranged from 2.0 × 106 to 1.1 × 108 cm−2, and the calcium ion column densities ranged from 1.6 × 106 to 4.2 × 108 cm−2. The mean centroid heights of Ca+ and Ca are 98.6 km and 93.0 km, respectively, and the centroid heights of Ca+ and Ca are mostly influenced by annual variations. The seasonal variation in the Ca+ and Ca layers in Beijing exhibits similarities to that of Kühlungsborn (54°N). While the peak density of Ca+ in Beijing are similar to those observed in Kühlungsborn, the peak density of the Ca layer in Beijing is about half of that reported in the Ca layer at 54°N. We provide an explanation for the disparities in the column abundance and centroid altitude of the Ca layer between Yanqing and Kühlungsborn, discussing variations in neutralization among different metal ions.

Adsorption behavior of H2O on the strontium bromide surface: first-principles and molecular dynamics calculations.

Thermochemical adsorption heat storage based on gas-solid interaction is an energy storage technology for the effective recovery of industrial waste heat and renewable energy sources such as solar energy. Currently, hygroscopic salts and water are commonly used as the working pairs in thermochemical thermal storage systems. Strontium bromide (SrBr2) is a highly potential material for low-grade thermal energy storage and building applications due to its high sorption capacity and reaction enthalpy. In order to better understand the microscopic mechanism of adsorption, the water adsorption behavior of strontium bromide surfaces on the atomic scale is investigated in this study by using density functional theory (DFT). The effects of doping Ca or Mg into strontium bromide on water adsorption are analyzed by the comparison of the energy barrier, density of states (DOS) and crystal orbital Hamilton population (COHP) obtained before and after metal atom doping. The energy barrier of the SrBr2/H2O reaction system is 5.916 kcal mol-1, and the energy barrier of Ca-doped SrBr2 reduces to 3.432 kcal mol-1, whereas the energy barrier of Mg-doped SrBr2 increases to 13.394 kcal mol-1. The thermodynamic properties of strontium bromide are significantly improved by doping with calcium atoms. The absolute value of the COHP for Ca-doped SrBr2 decreases, which indicates that Ca-doped SrBr2 can adsorb the H2O molecules more easily at the same temperature. The doping of Ca atoms has a positive effect on the adsorption heat storage process. This study provides insight into the adsorption mechanism of water molecules on strontium bromide and could facilitate the design of efficient composite adsorbents.

Nitridochromate(IV) fluoride - LiCa8[CrN3]2N2F.

LiCa8[CrIVN3]2N2F (Pnnm (#58), a = 17.5230(13) Å, b = 7.3379(5) Å, c = 4.9433(4) Å) is an example of a multinary nitridochromate fluoride, that provides additional information on almost elusive tetravalent nitridochromates. Shorter Cr-N bond lengths compared to those in the previously reported nitridochromates(III), as well as diamagnetic behavior and vibrational spectroscopy data suggest Cr(IV), which is in good agreement with the charge balance and crystal structure refinement. According to band structure calculations, LiCa8[CrIVN3]2N2F is a semiconductor with a band gap of 1.1 eV. The compound features trigonal planar [CrN3]5- units of Cs symmetry, and lithium, calcium, nitrogen and fluorine atoms arranged in a fragment of the rock salt type structure.

Zinc-Substituted Structures of Hydroxyapatite: Modeling and Experiment

The results of calculations of the substitution of calcium atoms for zinc in the structure of hydroxyapatite using density functional theory methods using hybrid functionals in the supercell model are presented. Changes in the parameters and volume of the unit cell, energy bands and energy of formation of substitutions with increasing number of substitutions in different positions of calcium (Ca1 and Ca2) are analyzed in comparison with experimental data. A proportional decrease in the parameters and volume of the cell with an increase in the number of substitutions has been established, and a more complex behavior of various cell parameters has been revealed, which is a consequence of the violation of the original symmetry. Electronic energy levels were found to depend on the zinc concentration and the positions of the calcium ions being replaced. In this case, the band gap Eg of hydroxyapatite experiences a jump of 0.6–0.8 eV with the introduction of one zinc ion per supercell, and then decreases and reaches values below the initial Eg value by 0.5–0.6 eV for substitutions in Ca1 positions, and by 0.8–0.9 eV for substitutions in Ca2 positions. It has been shown that the energy of substitution has a complex dependence on the concentration of the substituent and the replacement of calcium ions with zinc occurs predominantly in the Ca2 position over the entire concentration range. An analysis of changes in interatomic distances during the process of relaxation to the equilibrium state at different zinc concentrations was carried out. We revealed formation of bonds between zinc atoms and nearby oxygen anions, which violates the original symmetry of hydroxypatite structures. The data obtained are important for understanding the structural changes that occur during substitution, as well as for understanding and predicting the properties of synthesized biocompatible materials.

New promising class of anode materials for Ca-ion battery: polyaromatic hydrocarbons

Using first-principles calculations we propose new anode materials for calcium-ion batteries, namely anthracene (AN), tetracene (TN) and pentacene (PN) crystals. We show that adsorption of calcium atoms on isolated AN, TN and PN molecules is energetically favorable, as well as intercalation into bulk crystals in a wide range of calcium concentrations. For all crystals, volume expansion during intercalation is less than 20% and for pentacene, it is less than 8%. We assess the diffusion and electronic properties of AN, TN and PN. We show that calcium diffusion barriers along the polyacene molecules are less than 0.45 eV, but calcium diffusion is limited by “jumps” between the molecules. Sequential band filling upon increasing levels of intercalation leads to the reentrant semiconducting-metallic-semiconducting behavior. Our results point to the promise of anthracene, tetracene, and pentacene as anodes for calcium-ion batteries.

Nanoscale insight into fluidity improvement of supplementary cementitious materials on concrete: The nano-lubrication process

The workability of concrete is a fundamental property that is frequently influenced by chemical admixtures. In this paper, we provide an interesting perspective to understand the effect of silica fume on the fluidity of cement slurries. By employing molecular dynamics techniques, a nanoscale boundary friction model is proposed to evaluate the flow of cement slurries resulting from cement hydration. According to conventional experimental data, interfacial friction decreases as the water content rises. And additional lubrication of the silica surface is possible. The investigation into the microscopic mechanisms behind interfacial lubrication reveals that water lubricates SiO2 and CSH sheets in various ways at low and high water levels. Throughout the system, non-covalent water-water and water-calcium bonds break down during the lubricating process. It appears that some calcium atoms are split out of the CSH matrix, a sign of a covalent break. In the high water content system, this separation did not happen despite the lubricating action in the low water content system. It is also possible to visually evaluate the impact of additional cementitious materials on the cement paste's fluidity by using the recently discovered mechanism.

Synthesis of magnesium-containing calcium phosphates by methods of chemical precipitation in aqueous solutions and solid-state interaction

The peculiarities of the partial isovalent substitution of calcium atoms by magnesium in the structure of -Са3(РО4)2 within the compositions of Ca10.5–хMgx(PO4)7 (х=0.4, 0.8, 1.0 and 1.5) were investigated by methods of chemical precipitation in aqueous solutions and solid-state interaction. In the first case, the biphasic calcium phosphates (based on Са10(РО4)6(ОН)2 and -Са3(РО4)2) doped with magnesium cations as well as monophasic Ca9.5Mg(PO4)7 and Ca9Mg1.5(PO4)7 (whitlockite-related, trigonal system, space group R-3c) were prepared as a result of mixing aqueous solutions at molar ratios Ca2+:Mg2+:PO43–=(10.5–x):x:7 (where x=0.4, 0.8, 1.0 and 1.5), with further evaporation of water and heating of the solid residue at a temperature of 6000С (for 2 hours). The biphasic calcium phosphates were also obtained by the solid-state interaction of initial components at the temperature range of 500–7000С (for 6 hours) and the same molar ratios Ca2+:Mg2+:PО43–=(10.5–х):х:7 (х=0.4, 0.8, 1.0 and 1.5). It was found that only the apatite-type phase (Са10(РО4)6(ОН)2) contains magnesium, and the content of this phase in the biphasic composites increases with the growing of magnesium amount in the initial mixtures. The established conditions of the formation of single phasic whitlockite-related magnesium-containing calcium phosphates as well as biphasic composites of modified calcium phosphates can be used in the future to obtain bioactive materials for medical purposes.

The scale inhibition mechanism of sodium humate on heat transfer surface: Insights from electrochemical experiments, quantum chemical calculations, and molecular dynamics simulation

The scale inhibition mechanism of sodium humate (HAS) on Calcium Carbinate (CaCO3) was investigated by experiments, quantum chemical calculations and molecular dynamics simulations. The changes of electrochemical impedance spectroscopy were analyzed by electrochemical methods at different concentrations (0, 10, 30, 50, 70, 100 mg/L) of HAS. The molecular structure of HAS was optimized by quantum chemical calculation, and the charge distribution, electrostatic potential distribution and frontier orbital energy of HAS were obtained. The interaction simulation system between HAS and the crystal planes of calcite was constructed based on molecular dynamics simulation. The interaction mechanism between specific functional groups in HAS and calcite crystal plane was analyzed. The results show that the capacitance arc and charge transfer resistance increase with the increase of HAS concentration in the range of 0–50 mg. However, In the concentration range of 50–100 mg, the capacitance arc and charge transfer resistance decrease with the increase of concentration. In the optimized structure of HAS, the oxygen atom on the carboxyl group is more negatively charged. There is a strong mutual attraction between HAS and calcite crystal plane. The primary functional group responsible for achieving scale inhibition is formed through the bonding between the carboxyl oxygen atom within its molecular structure and the calcium atom on the calcite crystal plane. The research in this paper provides a strong guidance for the treatment of scale and the development of scale inhibitors.

Lithium doping effect on structural, electronic and optical properties of KCaF3 fluoroperovskite: DFT insights using GGA-PBE

In order to evaluate the effects of Lithium (Li) doping on the various properties of KCaF3, we present first-principles calculations built on density functional theory (DFT) and employing approximation GGA-PBE. The compound possesses a 2 × 2 × 1 supercell and cubic geometry with space group pm3m. By putting the TDOS and PDOS concepts into practice, the effects of Li-doping on electronic structure and, consequently, optical characteristics have been investigated and evaluated in detail. With the formation of new states in band structure, the substitution of the Lithium (Li) atom for the Calcium (Ca) atom drastically adjusts the electronic band structure. The indirect bandgap of pure KCaF3 was measured to be 5.37 eV. The band gap was slightly shrunk as a result of changes in Li concentration. This causes the indirect band gap of KCaF3 to change to the direct band gap for Li-doped KCaF3. A strong interaction between the Li atom and the atoms around it is seen and the density of states for Li-doped KCaF3 relocates at slightly lower energies. Additionally, there is a noticeable change in the partial density of states of KCaF3 near the conduction band bottom, leading us to believe that Li-doping has an impact on the electronic band structure. Investigations into the optical characteristics of doped and undoped KCaF3 and correlations with its electrical structure are made. The massive difference in optical characteristics and band gap (i.e., indirect to direct) caused by Li-doping makes this substance a desirable candidate for optoelectronic materials.

Adsorption of Ca on borophene for potential anode for Ca-ion batteries.

Two-dimensional borophene can be used in rechargeable batteries due to its high specific surface area. In this paper, the performance of borophene as an anode material for calcium ion batteries is predicted based on density functional theory calculations. The calculation results show that P doping enhances the calcium storage properties of borophene. The maximum adsorption number of calcium atoms in the P-doped system is 7, with a theoretical capacity of 964 mAh/g. DOS analysis showed that borophene exhibited metallic properties after adsorbing calcium atoms, which improved the electrical conductivity of the electrode material. Calculation of the diffusion energy barrier shows that strain has an effect on calcium diffusion in monolayer borophene, and compressive strain promotes calcium diffusion through borophene. The findings suggest that borophene may be a promising electrode material for calcium-ion batteries. In this paper, the intrinsic model and doping model of borophene are constructed by Material Studio 8.0, and the first-principles calculation is carried out by CASTEP module.

Atomically dispersed calcium as solid strong base catalyst with high activity and stability

Solid strong base catalysts are highly attractive for diverse reactions owing to their advantages of neglectable corrosion, facile separation, and environmental friendliness. However, their widespread applications are impeded by basic components aggregation and low stability. In this work, we fabricate single calcium atoms on graphene (denoted as Ca1/G) by use of a redox strategy for the first time, producing solid strong base catalyst with high activity and stability. The precursor Ca(NO3)2 is first reduced to CaO at 400 °C by the support graphene, forming CaO/G with conventional basic sites, and the subsequent reduction at 850 °C results in the generation of Ca1/G with atomically dispersed Ca. Various characterizations reveal that Ca single atoms are anchored on graphene in tetra-coordination (Ca–C2–N2) where N is in situ doped from Ca(NO3)2. The atomically dispersed Ca, along with their anchoring on the support, endow Ca1/G with high activity and stability toward the transesterification reaction of ethylene carbonate with methanol. The turnover frequency value reaches 128.0 h−1 on Ca1/G, which is much higher than the traditional counterpart CaO/G and various reported solid strong bases (2.9–46.2 h−1). Moreover, the activity of Ca1/G is well maintained during 5 cycles, while 60% of activity is lost for the conventional analogue CaO/G due to the leaching of Ca.

Depression mechanism of novel organic phosphoryl depressants on calcite: DFT and coordination studies

Calcite, a commonly encountered gangue mineral, is often found associated with precious metal minerals. The separation of calcite from metallic minerals is typically achieved through flotation, necessitating the development of efficient and targeted calcite depressants. This study focuses on investigating the depressant effects of three novel calcite depressants containing phosphoryl groups, namely aminotrimethylene phosphonic acid (ATMP), tetrasodium (HEDP), and diethylenetriaminepentakis (DTPMPA), through micro-flotation experiments. The obtained flotation results demonstrated the successful depression of calcite by all three reagents, with DTPMPA exhibiting the most pronounced depressing effect. Moreover, density functional theory (DFT) analysis revealed that DTPMPA possessed superior depressant capabilities on the calcite surface compared to the other two novel depressants. Coordination studies further elucidated that phosphoryl groups can form stable 6-coordination structures with calcium atoms on the calcite surface, with the coordination ability being influenced by the molecular properties of the reagents. These findings hold significant implications for achieving an efficient separation of calcite from metallic minerals, emphasizing the importance of developing high-efficiency and targeted calcite depressants.