Light Alkali Metals Research Articles

Limits of Laser Cooling of Light Alkali Metals in a Polychromatic Light Field

A model was developed for laser cooling of alkali atoms in a polychromatic field, considering the real structure of atomic levels. The model was tested by the example of the 6Li atom. The minimum achievable temperatures of laser cooling of light alkali atoms were studied for different polarizations of the light field components, and the possibility of cooling below the Doppler limit was shown.

Potassium doping for grain boundary passivation and defect suppression enables highly-efficient kesterite solar cells

The complicated and diverse deep defects, voids, and grain boundary in the CZTSSe absorber are the main reasons for carrier recombination and efficiency degradation. The further improvement of the open-circuit voltage and fill factor so as to increase the efficiency of CZTSSe device is urgent. In this work, we obtained K-doped CZTSSe absorber by a simple solution method. The medium-sized K atoms, which combine the advantages of light and heavy alkali metals, are able to enter the grain interior as well as segregate at grain boundary. The K-Se liquid phase can improve the absorber crystallinity. We find that the accumulation of the wide bandgap compound K2Sn2S5 at grain boundary can increase the contact potential difference of grain boundary, form more effective hole barriers, and enhance the charge separation ability. At the same time, K doping passivates the interface as well as bulk defects and suppresses the non-radiative recombination. The improved crystallinity, enhanced charge transport capability and reduced defect density due to K doping result in a significant enhancement of the carrier lifetime, leading to 13.04 % device efficiency. This study provides a new idea for simultaneous realization of grain boundary passivation and defect suppression in inorganic kesterite solar cells.

Isolable rubidium and caesium derivatives of common organic carbonyl compounds.

Light alkali metal (Li, Na, K) amides have a long history of synthetic utility, but heavier (Rb, Cs) congeners have barely been studied. This study reveals remarkable structurally complex outcomes of reacting AM(HMDS) (AM = Rb, Cs; HMDS = hexamethyldisilazide) with benzaldehyde and acetophenone. Though complicated, reactions give a diversity of eye-catching isolated products, an enolate with a hexagonal prismatic network, two dienolates with distinct extended ladder motifs, and two β-imino-alkoxides comprising zig-zag chains of metal-oxygen bonds in infinite cages.

Imaging a ^{6}Li Atom in an Optical Tweezer 2000 Times with Λ-Enhanced Gray Molasses.

We have imaged lithium-6 thousands of times in an optical tweezer using Λ-enhanced gray molasses cooling light. Despite being the lightest alkali metal, with a recoil temperature of 3.5 μK, we achieve an imaging survival of 0.999 50(2), which sets the new benchmark for low-loss imaging of neutral atoms in optical tweezers. Lithium is loaded directly from a magneto-optical trap into a tweezer with an enhanced loading rate of 0.7. We cool the atom to 70 μK and present a new cooling model that accurately predicts steady-state temperature and scattering rate in the tweezer. These results pave the way for ground state preparation of lithium en route to the assembly of the LiCs molecule in its ground state.

Assessment of lithium bioaccumulation by quinoa (Chenopodium quinoa willd.) and its implication for human health.

Lithium (Li) is the lightest alkali metal and 27th most abundant element in the earth crust. In traces, the element has medicinal value for various disorders in humans, however, its higher concentrations may lead to treatment-resistant depression and altered thyroid functioning. Quinoa (Chenopodium quinoa) has gained popularity owing to its halophytic nature and its potential use as an alternative to the traditional staple foods. However, quinoa response to Li-salt in terms of growth, Li accumulation potential and health risks associated with consumption of the quinoa seeds grown on Li-contaminated soils has not been explored yet. During this study, quinoa was exposed to various concentrations of Li (0, 2, 4, 8 and 16mM) at germination as well as seedling stages. The results showed that seed germination was the highest (64% higher than control) at Li concentration of 8mM. Similarly, at 8mM doses of Li shoot length, shoot dry weight, root length, root dry weight and grain yield were increased by 130%, 300%, 244%, 858% and 185% than control. It was also revealed that Li increased the accumulation of calcium and sodium in quinoa shoots. Carotenoids contents were increased, but chlorophyll contents remained un-changed under Li application. The activities of antioxidants viz. Peroxide dismutase, catalase and super oxide dismutase were also increased with an increase in the levels of Li in the soil. Estimated daily intake and hazard quotient of Li in quinoa were less than the threshold level. It was concluded that Li concentration of 8mM is useful for quinoa growth and it can be successfully grown on Li contaminated soils without causing any human health risks.

Lithium Ion Wave Function (3Li2+) in a Momentum Chamber at n?3

Lithium ion (3Li2+) is a light alkali metal which is reactive and flammable when exposed to water or air. Lithium becomes ionic when lithium metal loses two of its three valence electrons. The wave function is a complex quantity that shows the characteristics of the de Broglie wave. The wave function in question is the radial wave function in the particle, because to find the probability that the electron is in the particle, only the radial part of the wave function is needed. However, there is no literature that discusses the wave function in the momentum space in the case of hydrogenic ions. Therefore, this research will examine the wave function of Lithium ion (3Li2+) in the momentum space. This type of research in the preparation of this article uses non-experimental research. Based on the results of the research that has been done, the wave function of Lithium ion (3 Li2+) in the momentum space at n 3 is obtained. The wave function consists of a radial, angular (polar and azimuth) wave function, as well as the wave function of Lithium ion (3Li2+) as a whole. The fundamental difference between the wave function of Lithium ion (3Li2+) in the momentum space and the wave function of hydrogenic atoms in the other momentum space is the value of the radial function caused by the difference in the value of (z) or atomic number.

Quantitative analysis of Li, Na and K in single-element standard solutions using portable laser-induced breakdown spectroscopy

Laboratory-based laser-induced breakdown spectroscopy (LIBS) instruments have proven themselves for trace element analysis of an extensive range of elements. As portable devices have evolved greatly in recent years, new areas of field application are opening up. However, no portable LIBS (pLIBS) has yet been used for quantitative inorganic water analysis. The aim of this study was to explore whether pLIBS combined with a surface-enhanced liquid-to-solid conversion method can quantify light alkali element concentrations in standard solutions. Multivariate calibrations were performed with single-element standard solutions at detection limits of 0.006, 0.011 and 0.007 mg l −1 for Li, Na and K, respectively. Coefficients of determination ( R 2 ) for the calibration lines from 0.1 to 100 mg l −1 for Li and Na, and 0.1 to160 mg l −1 for K were between 0.96 and 0.99. It has been shown that the surface preparation technique used improves the homogeneity of the spread and shape of the evaporation residue and thus the accuracy and precision of the analysis. Hence, this study demonstrates that it is possible to quantify light alkali metals in single-element standard solutions in the range of 0.1 to 160 mg l −1 using handheld LIBS.

Dielectric response and polarization mechanism of alkali silicate glasses in gigahertz to terahertz frequency range

AbstractOxide glasses are dielectric materials with potential applications in high‐frequency communications; hence, their dielectric properties in the gigahertz to terahertz frequency range should be investigated. In this study, the dielectric properties of silica glass and five single alkali silicate glasses were measured at 0.5–10 THz using terahertz time‐domain spectroscopy and far‐infrared spectroscopic ellipsometry. At 0.5–10 THz, the silica glass exhibited low dielectric dispersion with a low dielectric constant and loss. By contrast, the alkali silicate glasses exhibited high dielectric dispersion, and the dielectric constant and loss were higher than those of the silica glass. The shape of the dielectric dispersion profile depended on the alkali‐metal ions; it was broader for lighter ions such as Li ions and sharper for heavier ions such as Cs ions. The peak dielectric loss shifted toward a lower frequency as the weight of the alkali‐metal ions in the alkali‐silicate glass increased. To understand the dielectric dispersion, the complex permittivity was calculated using molecular dynamics simulations. The theoretical results qualitatively agreed with the experimental data. Ion dynamics analysis revealed that alkali‐metal ions vibrate and migrate under an applied electric field, which affects the dielectric constant and loss of alkali‐silicate glasses at gigahertz to terahertz frequencies. To fabricate filter devices at low temperatures, alkali metals should be added to silicate glass; therefore, a minimum amount of light alkali metals should be used to minimize the dielectric loss of the glass materials while maintaining productivity.

Influence of ion beam surface treatment on the emission performance of photocathodes.

Photocathodes are mainly used in such hi-tech fields as photoelectric conversion devices, radiation detection, and accelerators. Laser-driven photocathodes are characterized by low emission, high brightness, easy control, rapid response, etc., and are hopeful to become satisfactory electron sources for next-generation high-frequency miniaturized electric vacuum microwave devices, to effectively improve the performance and rapid response capability of the devices. For this reason, based on previous research efforts on photocathodes, we proposed an idea that ion beam surface treatment technology was used to modify the substrate surface of photocathodes and make the surface textured, enhancing the light absorptivity and alkali metal adsorption performance of photocathodes, so as to improve their emission performance. The surface appearance of photocathodes was analyzed using the scanning electron microscope (SEM) method, and it was found that the surface of oxygen-free copper treated by ion bombardment had a nanocone structure. The photoemission characteristics of photocathodes before and after the treatment of the surface of oxygen-free copper were studied. Before and after the treatment, the maximum photoemission current densities under stable emission performance of the photocathode were 60.5 mA cm−2 and 146.0 mA cm−2, respectively, and the calculated quantum efficiencies were 2.67 × 10−3 and 1.71 × 10−2, respectively. The quantum efficiency of the photocathode was increased by 5.41 times after the ion surface treatment. The results show that the photoemission quantum efficiency of the oxygen-free copper surface was increased greatly after modification. It was believed through analysis that the main cause for the increase in quantum efficiency was the enhancement of light absorptivity and the increase in the emission surface area.

Polyacrylonitrile/Crown Ether Composite Nanofibres With High Efficiency for Adsorbing Li(I): Experiments and Theoretical Calculations

Lithium, as the lightest alkali metal, is widely used in military and new energy applications. With the rapid growth in demand for lithium resources, it has become necessary to improve the effectiveness of extraction thereof. By using chemical grafting and electrospinning techniques, nanofibres containing crown ether were developed for adsorbing Li(I) from the brine in salt lakes, so as to selectively adsorb Li(I) on the premise of retaining specific vacancies of epoxy groups in crown ether. In lithium-containing solution, the adsorbing materials can reach adsorption equilibrium within three hours, and the maximum adsorption capacity is 4.8 mg g−1. The adsorption mechanisms of the adsorbing materials for Li(I) were revealed by combining Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) with density functional theory (DFT) calculation. The results indicated that in crown ether, O in epoxy groups was coordinated with Li(I) to form Li–O and four O atoms in the epoxy groups were used as electron donors. After coordination, two O atoms protruded from the plane and formed a tetrahedral structure with Li(I), realising the specific capture of Li(I). By desorbing fibres that adsorbed Li(I) with 0.5-M HCl, the adsorption capacity only decreased by 10.4% after five cycles, proving ability to regenerate such materials. The nanofibres containing crown ether synthesised by chemical grafting and electrospinning have the potential to be used in extracting lithium resources from the brine in salt lakes.

Alkali-Metal-Mediated Reversible Chemical Hydrogen Storage Using Seawater.

The economic viability and systemic sustainability of a green hydrogen economy are primarily dependent on its storage. However, none of the current hydrogen storage methods meet all the targets set by the US Department of Energy (DoE) for mobile hydrogen storage. One of the most promising routes is through the chemical reaction of alkali metals with water; however, this method has not received much attention owing to its irreversible nature. Herein, we present a reconditioned seawater battery-assisted hydrogen storage system that can provide a solution to the irreversible nature of alkali-metal-based hydrogen storage. We show that this system can also be applied to relatively lighter alkali metals such as lithium as well as sodium, which increases the possibility of fulfilling the DoE target. Furthermore, we found that small (1.75 cm2) and scaled-up (70 cm2) systems showed high Faradaic efficiencies of over 94%, even in the presence of oxygen, which enhances their viability.

Lithium-, Sodium-, and Potassium-ion Conduction in Polymeric and Discrete Coordination Systems

Abstract Coordination compounds have been increasingly studied as a new class of promising candidates for the matrix of ionic conducting materials because of their designability and high crystallinity. The ionic conduction of light alkali metal ions (Li+ and Na+) has been developed in polymeric coordination systems, which are commonly used under nonaqueous conditions. Recent studies have shown that discrete coordination compounds, as well as hydrated polymeric coordination compounds, can function as excellent ionic conductors even for heavier K+.

Narrowing of the Absorption Line of Light Alkali Metal Atoms in an Atmosphere of Heavy Inert Gases at Growing Radiation Intensity

The effect of narrowing of the absorption line of light alkali metal 7Li and 23Na atoms present in an atmosphere of heavy inert gas (xenon) with an increase in the external radiation intensity has been investigated. For 7Li atoms at temperature T = 300 K and buffer gas (Xe) pressure $${{p}_{{{\text{Xe}}}}} = 0.002$$ Torr, the linewidth at half maximum decreases by a factor of 1.20 with an increase in the radiation intensity from 1 µW/cm2 to 2.5 mW/cm2. For 23Na atoms at T = 600 K and $${{p}_{{{\text{Xe}}}}} = 0.01$$ Torr, the linewidth at half maximum decreases by a factor of 1.29 with an increase in the radiation intensity from 1 µW/cm2 to 6 mW/cm2. The effect of field narrowing of the absorption line is due to the following factors. First, the collisional relaxation of the velocities of light resonance particles in an atmosphere of heavy buffer particles is divided into two stages with significantly different durations: relaxation in the velocity direction (fast stage) and relaxation in the velocity magnitude (slow stage). Second, there are no collisional transitions between hyperfine components of the ground state.

Antiferromagnetic Kitaev interaction in f -electron based honeycomb magnets

We theoretically propose a family of $f$-electron based magnets that realizes Kitaev-type bond-dependent anisotropic interactions. Based on {\it ab initio} calculations, we show that $A_2$PrO$_3$ ($A$: alkali metals) crystalize in a triclinic structure with honeycomb layers of edge-sharing PrO$_6$ octahedra. Each Pr$^{4+}$ cation has a $4f$ electron in the $\Gamma_7$ doublet, which comprises a spin-orbital entangled Kramers pair with the effective moment $J_{\rm eff}=1/2$. By using the Wannier orbitals from the {\it ab initio} calculations, we find that the effective interactions between the $J_{\rm eff}=1/2$ moments are predominantly of {\it antiferromagnetic} Kitaev type for light alkali metals $A$=Li and Na, in stark contrast to the ferromagnetic ones in $4d$- and $5d$-electron based materials. Our finding would provide a playground for the Kitaev spin liquids that is hard to be accessed by the candidates ever discovered.

Titanium Carbene Complexes Stabilized by Alkali Metal Amides

Facile α-H elimination from tetrakis(trimethylsilylmethyl)titanium precursors to give adducts of (alkylidene)bis(alkyl)titanium complexes is induced by light alkali metal amides of the NNNN-type macrocyclic anionic ligand Me3 TACD [(Me3 TACD)H=1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane]. In the crystal, the alkali metal interacts with the carbene carbon atom or with the CH2 group of the trimethylsilymethyl ligand. The nucleophilic character of the carbene carbon atom was shown by the reaction with benzophenone and terminal acetylenes.

Cужение линии поглощения легких атомов щелочных металлов в атмосфере тяжелых инертных газов при росте интенсивности излучения

Abstract The effect of narrowing of the absorption line of light alkali metal ^7Li and ^23Na atoms present in an atmosphere of heavy inert gas (xenon) with an increase in the external radiation intensity has been investigated. For ^7Li atoms at temperature T = 300 K and buffer gas (Xe) pressure $${{p}_{{{\text{Xe}}}}} = 0.002$$ Torr, the linewidth at half maximum decreases by a factor of 1.20 with an increase in the radiation intensity from 1 µW/cm^2 to 2.5 mW/cm^2. For ^23Na atoms at T = 600 K and $${{p}_{{{\text{Xe}}}}} = 0.01$$ Torr, the linewidth at half maximum decreases by a factor of 1.29 with an increase in the radiation intensity from 1 µW/cm^2 to 6 mW/cm^2. The effect of field narrowing of the absorption line is due to the following factors. First, the collisional relaxation of the velocities of light resonance particles in an atmosphere of heavy buffer particles is divided into two stages with significantly different durations: relaxation in the velocity direction (fast stage) and relaxation in the velocity magnitude (slow stage). Second, there are no collisional transitions between hyperfine components of the ground state.

Hydrogen bonding in alkali metal cation-bound i-motif-like dimers of 1-methyl cytosine: an IRMPD spectroscopic and computational study.

The structures of alkali metal cation bound 1-methylcytosine (1-mCyt) dimers were explored using vibrational spectroscopy in the form of infrared multiple photon dissociation (IRMPD) spectroscopy and by computational methods. For the smaller alkali metal cations, Li+ and Na+, only non-hydrogen bonded symmetric anti-parallel structures were observed in agreement with the lowest energy computed structures. For K+, Rb+, and Cs+ the vibrational spectra in the N-H stretch region showed strong evidence for hydrogen bonding in agreement with the lowest energy structures which contained hydrogen bonding interactions between the amine group of one cytosine and the carbonyl oxygen of the other cytosine. The lowest energy structures for these complexes were compared to previously studied cytosine complexes [(Cyt)2M]+ where M = Li, Na, and K. The calculations are in agreement that only the non-hydrogen bonded structures would be observed for these cytosine complexes.

High-pressure vibrational properties of dense rubidium

At ambient conditions, alkali metals adopt the body centered cubic structure, while if compressed up to tens of GPa and above, they exhibit complex low-symmetry modifications, due to the density-driven transition of the valence electrons from the $s$ state to states of higher angular momentum. These high-pressure, low-symmetry phases, whose unit cells may include up to tens of atoms, allow rich Raman activity, which was previously observed only in lighter alkalis Na and Li. Here we report an extensive study of the optical phonons of highly dense Rb up to 100 GPa in diamond anvil cells, conducted by challenging experimental Raman spectroscopy measurements and ab initio computer simulations. The relative (relative to the normal condition value) density behavior of Raman frequencies of Rb is compared to that of Na and Li, once the frequencies of the two light alkali elements have been rescaled by $\sqrt{{M}_{\mathrm{Na}}/{M}_{\mathrm{Rb}}}$ and $\sqrt{{M}_{\mathrm{Li}}/{M}_{\mathrm{Rb}}}$, respectively, where ${M}_{\mathrm{Na}}$, ${M}_{\mathrm{Li}}$, and ${M}_{\mathrm{Rb}}$ are the atomic masses of the here considered alkali elements. Importantly, while the rescaled density behaviors of Na and Li agree with each other, Rb significantly differs, which highlights the different nature of the valence electron transition being of the $s\text{\ensuremath{-}}d$ and of the $s\text{\ensuremath{-}}p$ type in heavy and light alkali metals, respectively, a result that calls for further similar investigations of K and Cs.

Hypervalent Hydrosilicates Connected to Light Alkali Metal Amides: Synthesis, Structure, and Hydrosilylation Catalysis.

When light alkali metal amides [M(Me3 TACD)]n (M=Li, Na, K; (Me3 TACD)H=1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane) were treated with H2 SiPh2 in THF, [M{(H2 SiPh2 )Me3 TACD}(thf)x ] containing a pendant hypervalent dihydridosilicate were formed and characterized by elemental analysis, NMR/IR spectroscopy, and single-crystal X-ray crystallography. The lithium complex catalyzed the hydrosilylation of styrene derivatives under mild conditions with anti-Markovnikov regioselectivity.

A Reduced Sodium Titanate/Carbon Composite As a Stable, High-Energy Sodium Ion Battery Anode Material

The use of renewable but intermittent energy sources, such as solar and wind energy, means that it is necessary to store this energy for later use. Hence, a shift towards renewable sources of energy requires the development and use of efficient and inexpensive large-scale energy storage devices. Whereas portable electronics conventionally utilize lithium ion batteries (LIBs), this is not an option for large-scale energy storage, since the increased demand for lithium would result in a significant price increase. Therefore, alternative technologies, such as sodium ion batteries (SIBs) should be considered1. Since sodium is widely available across the globe, and is the lightest alkali metal after lithium, SIBs can be a valuable alternative to LIB technologies, despite the lesser reducing nature of sodium. Because of dendrite formation, the use of sodium metal as anode results in a significant safety hazard. Therefore, it is a better option to use a technology where sodium ions are not reduced to their metallic form. Potential alternative SIB anodes are mainly carbonaceous materials, alloys and phosphorus/phosphide, as well as oxides and polyanionic compounds2. However, many reported SIB anode materials suffer from a variety of disadvantages, such as a low electrochemical stability and energy density. Therefore, one of the challenges that the commercialization of SIBs faces is the development of a suitable anode material. Recently, a reduced sodium titanate was reported as SIB anode. However, its low electrochemical stability, together with its cumbersome synthesis method and the lack of understanding of the mechanism of sodium ion intercalation, makes its use in a commercial SIB unlikely. Our density functional theory (DFT) calculations show that the material is an insulator due to its large band gap. Therefore, a new, convenient synthesis method was developed, which results in a composite of reduced sodium titanate with conductive amorphous carbon (NTO/C). This composite material was characterized by powder X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The formation mechanism was studied using thermogravimetric analysis (TGA) and electron paramagnetic resonance (EPR). The electrochemical characteristics were studied using galvanostatic cycling and the galvanostatic intermittent titration technique (GITT). Operando XRD was used to investigate the mechanism of sodium insertion. The NTO/C, with an average operation voltage of ~0.9 V vs. Na/Na+, shows a high electrochemical stability (89% capacity retention after 250 cycles at 1C), and high capacity (135 mAh g-1 at 0.1C, 105 mAh g-1 at 1C and 61 mAh g-1 at 10C). Consequently, this NTO/C is currently the most energy dense material of all stable lithium-free SIB anode materials with an appropriate operation potential, even slightly surpassing O3-NaTiO2 3. As it also requires only abundant and inexpensive elements, we believe that NTO/C is an excellent material for commercial SIB anodes. Slater, M. D., Kim, D., Lee, E. & Johnson, C. S. Sodium-ion batteries. Adv. Funct. Mater. 23, 947–958 (2013).Yabuuchi, N., Kubota, K., Dahbi, M. & Komaba, S. Research Development on Sodium-Ion Batteries. Chem. Rev. 114, 11636–11682 (2014).Wu, D. et al. NaTiO2: a layered anode material for sodium-ion batteries. Energy Environ. Sci. 8, 195–202 (2015).