Cation Masses Research Articles

Chaotic evolution of the energy of the electron orbital and the hopping integral in diatomic molecule cations subjected to harmonic excitation

We analysed the dynamics of the positively charged ions of diatomic molecules (X2+ and XY+), in which the bond is realized by the single electron. We assumed that the atomic cores separated by the distance R were subjected to the external excitation of the harmonic type with the amplitude A and frequency Ω. We found the ground states of ions using the variational approach within the formalism of second quantization (the Wannier function was reproduced by means of Gaussian orbitals). It occurred that, on the account of the highly non-linear dependence of the total energy on R, the chaotic dynamics of cores induced the chaotic evolution of the electronic Hamiltonian parameters (i.e. the energy of the electron orbital ε and the hopping integral t). Changes in cation masses or in the charge arrangement does not affect qualitatively the values of Lyapunov exponents in the A-Ω parameter space.

ION cyclotron resonance: Geomagnetic strategy for living systems?

ABSTRACTExcept for relatively few polarity reversals the magnitude of the magnetic dipole moment of the earth has remained constant since life first began, allowing evolutionary processes to integrate the geomagnetic field (GMF) into several biological functions. One of these, bearing the classical signature of an ion cyclotron resonance (ICR)-like interaction, results in biological change associated with enhanced proton transport. The wide range of cation masses over which this effect is found suggest a fundamental biological dependence on the GMF, one that functions equally well for electric as well as magnetic fields. Such generalization of ICR requires two things: transparency of tissues to the GMF and suitably tuned ELF resonant magnetic or electric fields. To complement the widely reported ICR responses to applied AC magnetic fields, we hypothesize the existence of weak endogenous ICR electric field oscillations within the cell. This equivalence implies that even in the absence of applied AC magnetic fields, biological systems will exhibit intrinsic GMF-dependent ion cyclotron resonance intracellular interactions. Many ICR effects that have been reported appear as antagonist pairs suggesting that the characteristics of the GMF have not only been incorporated into the genome but also appear to function in an endocrine-like manner.

Control of thermal conductivity with species mass in transition-metal dichalcogenides

In this paper, we examine how the behaviour of the thermal conductivity of bulk and monolayer transition-metal dichalcogenides XY2 in their 2-H form can be controlled with different choices of cation and anion masses. We employ a semi-ab-initio approach, which combines first-principles phonon eigensolutions, the elastic anharmonic Hamiltonian for phonon-phonon interactions, a quasi-harmonic scheme for the temperature-dependent Grüneisen's constant, and a relaxation-time solution of the Boltzmann transport equation. Our results confirm an earlier finding [Gu and Yang, Appl. Phys. Lett. 105, 131903 (2014)] that the thermal conductivity of 2-H MoS2 is lower than that of 2-H WS2 contrary to what would be expected from the relative masses of Mo and W and the relative stiffnesses of both compounds. In addition to confirming this anomaly as a result of the larger acoustic optical gap of WS2 relative to that of MoS2, it is found that where one constituent species is fixed, more profound changes on the thermal conductivity occur for different anion masses than for different cation masses. We explain how these behaviours arise from the dispersion relations of each compound and the anharmonic interactions of phonon modes, and its connection with the relative masses of the constituent species. This finding provides useful insight into which 2-H dichalcogenides might be suitable for which thermal applications.

Thermal conductivity of ternary III-V semiconductor alloys: The role of mass difference and long-range order

Thermal transport in bulk ternary III-V arsenide (III-As) semiconductor alloys was investigated using equilibrium molecular dynamics with optimized Albe-Tersoff empirical interatomic potentials. Existing potentials for binary AlAs, GaAs, and InAs were optimized to match experimentally obtained acoustic-phonon dispersions and temperature-dependent thermal conductivity. Calculations of thermal transport in ternary III-Vs commonly employ the virtual-crystal approximation (VCA), where the structure is assumed to be a random alloy and all group-III atoms (cations) are treated as if they have an effective weighted-average mass. Here, we showed that it is critical to treat atomic masses explicitly and that the thermal conductivity obtained with explicit atomic masses differs considerably from the value obtained with the average VCA cation mass. The larger the difference between the cation masses, the poorer the VCA prediction for thermal conductivity. The random-alloy assumption in the VCA is also challenged because X-ray diffraction and transmission electron microscopy show order in InGaAs, InAlAs, and GaAlAs epilayers. We calculated thermal conductivity for three common types of order (CuPt-B, CuAu-I, and triple-period-A) and showed that the experimental results for In0.53Ga0.47As and In0.52Al0.48As, which are lattice matched to the InP substrate, can be reproduced in molecular dynamics simulation with 2% and 8% of random disorder, respectively. Based on our results, thermal transport in ternary III-As alloys appears to be governed by the competition between mass-difference scattering, which is much more pronounced than the VCA suggests, and the long-range order that these alloys support.

Ternary crystals Sr1−y Eu y−x 2+Eu x 3+F2+x of fluorite phases with a variable europium valence and their thermal conductivity (50–300 K)

Crystals of new fluorite materials: ternary nonstoichiometric Sr0.9Eu0.086Eu0.014F2.014 and Sr0.5Eu0.432Eu0.068F2.068 phases with a structure of fluorite (CaF2) type, containing europium ions in different oxidation states (Eu2+, Eu3+), have been grown for the first time from a melt by the Bridgeman method. The variation in their thermal conductivity k(T) in a temperature range of 50–300 K has been experimentally studied. The equivalent cation positions with a large difference in cation masses (m Sr = 87.62 amu and m Eu = 151.96 amu) lead to low k(T) values of ternary (Sr1-yEuy-x 2+Eux 3+F2+x) and binary (Eu0.864 2+Eu0.136 3+F2.136) crystals. One can obtain crystals with thermal characteristics specified in a wide range by adjusting the ratio of strontium and europium (regardless of the valence). Since the thermal conductivity of Sr0.5Eu0.432Eu0.068F2.068 and Eu0.864Eu0.136F2.136 is independent of temperature in the range of 200–300 K, they can be recommended as reference materials with k(T) = const.

Revisiting the cation mass-valence sum approach to assigning infrared OH-bands in dioctahedral smectites in the light of new data from synthetic Ga-Fe3+ smectites

A series of pure Ga-Fe3+ smectites were synthesized at 180°C in order to complete IR data in the Al-Ga-Fe3+ system. MIR and NIR data from natural and synthetic smectites in the Al-Fe3+, Al-Ga and Fe3+-Ga chemical series exemplified a case where some ν OH, δ OH and (ν+δ) OH band positions did not follow the relation: ν OH (cm−1)=(1/2π c)*(kOH/μOH)1/2. This relation is often used to approximate the position of the OH vibration bands from the reduced masses of octahedral cations linked to hydroxyls in clay minerals. In this study, better relations were established between the wavenumbers of the OH absorption band of smectites and the average ionic radius of neighboring octahedral cations. Similar trends were established previously for M-(OH)2 hydroxides (G.W. Brindley, C. Kao, Phys. Chem. Miner. 10 (1984) 187-191) suggesting a possible generalization of a link between OH frequencies in IR spectra and the average ionic radii of neighboring octahedral cations for hydroxylated minerals.

Reactive matrices for matrix-assisted laser desorption/ionization mass spectrometry of primary amines.

Some aromatic carbonyl compounds [2,4-dihydroxybenzaldehyde (2,4-DHBA), 2,5- dihydroxyacetophenone (DHAP), 2,3,5-trihydroxybenzaldehyde and 2,4-dinitrobenzaldehyde] were examined as potential reactive matrices for the analysis of mono-, di-, and polyamines by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Although all the above compounds readily and quantitatively react with primary amines to form Schiff bases (the completeness of the reactions was proved by gas chromatography MS of derivatized aliphatic amines), only DHBA and DHAP provide efficient desorption/ionization under MALDI conditions. This means that two these aromatic carbonyl compounds can simultaneously exhibit properties of both derivatization agents and efficient matrices for MALDI-MS analysis. The use of such reactive matrices eliminates the need to perform additional derivatization experiments. With the aid of DHBA and DHAP, it was confirmed that each individual oligomer of polypropylene glycols and co- polyethylene/propylene glycols contained two terminal amino groups. To calculate the number of NH2 groups, mass increments of the introduced groups and a difference in the masses of cations attached to the initial and derivatized amines were used. The suggested approach, involving the application of the same reactive matrices, was applied to the determination of a number of NH(2) groups in individual oligomers of branched polyethyleneimines (PEIs) by MALDI-MS. In this case, DHAP appeared to be the best reactive matrix. The dependence of the number of NH(2) groups on the quantity of monomeric units and branching of each individual PEI oligomer is shown.

MD Study on the Thermal Conductivity of Molten Alkali Halides: Effect of Ionic Mass Difference

A definition suitable for the average ionic mass used for two kinds of expressions of the thermal conductivity for molten alkali halides has been explored from the viewpoint of the difference in anion and cation masses. One is the scaling equation, \({\lambda } \propto \)\(m^{-1/2}\)\((N/V)^{2/3}\), where \({m}\) is the average ionic mass between the anion and cation and \(N/V\) is the number density, which was previously obtained from molecular dynamics (MD) simulation. The other is the equation used in the corresponding-states (CS) analysis which has been applied to the thermal conductivities calculated by the MD simulation. Among some representative definitions, it turned out that a simple arithmetic average is best for the equation. As an estimation method of the thermal conductivity, it was shown that both equations have comparable precision. It was indicated that considering the difference in ionic masses between the anion and cation is important for building a more precise correlation in the CS analysis.

A molecular dynamics study of [111]-polarized gap discrete breathers in a crystal with NaCl-type structure

Molecular dynamics simulations show that a gap discrete breather (DB) polarized along the [111] direction can be excited in a crystal with NaCl-type structure and significantly different masses of anions and cations. The DB exists in both a nondeformed crystal and one subjected to significant uniaxial or biaxial elastic deformation. The dependence of the DB frequency on the amplitude at a given deformation is determined.

Influence of elastic strain on the density of phonon states and characteristics of discrete breathers in the gap of the phonon spectrum of a crystal with a NaCl structure

Appreciable elastic strain may considerably change the physical properties of crystals. This effect underlies the elastic stress technology, which has been intensively developed in recent years. The influence of elastic strain on the density of phonon states and on the properties of discrete breathers in the gap of the phonon spectrum of a crystal with a NaCl structure and a considerable difference between the anion and cation masses is studied using the molecular dynamics method. A number of crystal straining modes are considered. It is shown that the shear components of the strain tensor may significantly change the density of phonon states but slightly influence the frequencies of discrete breathers. Compression (tensile) strains raise (lower) the frequency of discrete breathers with a respective polarization.

Computational insight into the effect of monovalent cations on the electronic, optical, and lattice dynamic properties of XInSe2 (X = Cu, Ag, Li)

Interactions between monovalent cations and anions are common in ternary AIBIIIC2VI chalcopyrite crystals, and are known to significantly influence their electronic behaviors. Density functional theory was used to investigate the effect of monovalent cations on the electronic, optical, and lattice dynamic properties of XInSe2 (X = Cu, Ag, Li) compounds. It follows that the electronic configurations of X ions, as well as the interactions between X ions and InSe4 groups, are responsible for the different electronic and optical properties of XInSe2. The special lattice dynamic properties of LiInSe2 are mainly related to the smaller cationic masses of Li cations, whereas the high ionicity of Li–Se bonds leads to the anomalistic declines of the A1 and A2 modes and the greater LO/TO splitting of the upper phonon polar modes.

Effect of elastic deformation on phonon spectrum and characteristics of gap discrete breathers in crystal with NaCl-type structure

The influence of elastic deformation on the phonon spectrum and properties of the gap discrete breathers (DBs) in a crystal with the NaCl type structure and significantly different masses of anions and cations has been studied using the molecular dynamics method. Two modes of the crystal deformation were considered, including the (i) hydrostatic tension and compression and (ii) pure shear. It is established that the phonon densities of states are significantly changed in both cases, while the gap DB frequencies depend on the hydrostatic tension and compression and are almost independent of the pure shear.

Minerals from Macedonia. XXVI. Characterization and spectra–structure correlations for grossular and uvarovite. Raman study supported by IR spectroscopy

AbstractThe characterization and spectra–structure correlations of grossular and uvarovite garnets by Raman and infrared (IR) spectroscopy were carried out. Attention was focused on the explanation of the spectral differences between both minerals from structural and compositional points of view because they are isomorphous and share the general chemical formula [Ca3Y2(SiO4)3; Y = Al (grossular) and Cr (uvarovite)]. It was established that the prominent spectral differences are mainly due to the presence of various Y3+ cations and the possibility for their interchange. It was found that the substitution of Al3+ with Cr3+ promotes blue shifting of the high‐energy Raman bands (SiO4 stretchings) and red shifting of the corresponding IR bands. This peculiar observation is explained by the introduction of two different effects that promote band shifting in opposite directions—the effect of different cation crystal field stabilization energies versus the effect of different cation masses and radii. Copyright © 2010 John Wiley & Sons, Ltd.

Application of the sublattice method to the investigation of phonon spectra and frequency density of fluorite-structure crystals

Phonon spectra and state densities of MeF 2 (Me = Ca, Sr, Cd, Ba, or Pb) crystals are calculated in the basis of sublattice state vectors using the Born-Mayer model. The phonon spectra and the sublattice state densities are calculated in the field of the second frozen sublattice. It is demonstrated that optical crystal branches are mainly due to oscillations of fluorine ions; moreover, the topology of optical branches in the spectrum and the crystal state densities are close to the topology of the spectra and state densities of the fluorine sublattice in the frozen metal sublattice. Exception is CaF 2 whose ion and cation masses are close in values.

Cation mass-valence sum (CM-VS) approach to assigning OH-bending bands in dioctahedral smectites

AbstractThe assignments of OH-bending bands in the infrared (IR) spectra of dioctahedral smectites (montmorillonites, ferruginous smectites, and nontronites) have been revisited using a cation mass-valence sum (CM-VS) approach to quantify octahedral cation occupancy. The CM-VS approach enabled prediction of OH-bending band positions (in wavenumbers) related to OH-sharing octahedral cation pairs that had valence sums of 4 and 5, and cation masses associated with Fe(II) and Mg. Application of rules for the relationship enabled determination of the location of OH-sharing octahedral cation pairs containing Mg and Fe(II) for which previous assignments have been considered controversial, e.g. Fe(III)Mg-OH and MgMg-OH, or for which assignments have been missing due to lack of spectroscopic evidence, e.g. AlFe(II)-OH, Fe(III)Fe(II)-OH, Fe(II)Mg-OH, and Fe(II)Fe(II)-OH. Examples of these bands from several natural ferruginous smectites and nontronites are discussed. Quantification of IR spectra was used to develop a better understanding of the octahedral cation occupancy of this important class of Fe(III)-enriched smectites. While Fe(II) contents may be somewhat overestimated by the IR technique, those for four of the six ferruginous smectites studied here agree well with data from Mössbauer spectroscopy.

On the use of the 16O( 4He, 4He) 16O resonance for the evaluation of radiation damage in oxides

This paper deals with the evaluation of the radiation damage induced in the various sublattices of oxide single crystals submitted to irradiation with energetic ions. The study is focused on the depth distribution of the disorder (disorder profile) and the variation of the disorder as a function of the ion fluence (disordering kinetics). More specifically we discuss the pertinence of the use of the standard RBS or of the 16O( 4He, 4He) 16O resonance at 3.04 MeV for the study of the anionic sublattice in oxides with different cation masses. The experimental results obtained on several binary oxides indicate that the RBS mode is better suited for the study of oxides with low cation mass (e.g. SiO 2), whereas the resonant mode is more adapted to the study of oxides with high cation mass (e.g. UO 2). In the medium mass region (illustrated by ZrO 2), either the RBS or the resonant modes can be used depending whether the disorder profile or the disordering kinetics are evaluated.

Parameters and properties of crystals of ionic compounds obtained by centrifugal separation of supersaturated aqueous solutions

The change in the chemical composition, structural parameters, and properties of Ba(NO3)2, PbCl2, and KI crystals and the binary alkali-halide systems LiCl-KCl (eutectic) and LiCl-NaCl and KCl-KI (solid solutions) after centrifugal separation under acceleration (1.3, 6.2, 11.8)×103g is investigated. The composition variation was monitored by the methods of chemical gravimetric and titration analyses, as well as of flame-photometric and spectrophotometric analyses. Acceleration causes a change in the chemical composition, lattice parameter, refractive index, and microhardness in all systems as compared to the initial values. It is found that centrifugation affects the systems with different masses of cations more strongly than the systems with different masses of anions. A criterion of the ratio of the masses of ions (cations and anions) rat i/i is proposed for predicting the effect of centrifugation on the change in the chemical composition and properties of compounds and their systems (a larger value of this ratio leads to a stronger variation of the composition and properties). The crystals of all compounds and solid solutions display an increase in microinclusions (visible only in transmitted light) upon an increase in the acceleration. The lattice parameters and microhardness measured in KCl and KBr crystals four years after their fabrication by using centrifugal separation indicate a considerable return to their initial values.

The [formula omitted]– [formula omitted] (2,0) transition in 11BH and 10BH observed by (1+2)-photon resonance-enhanced multiphoton ionization spectroscopy

We report the mass-selected resonance-enhanced multiphoton ionization (REMPI) spectrum of photolytically produced diatomic boron hydride over the spectral range from 368 to 372 nm. Features recorded for time-of-flight-resolved cation masses 12, 11 and 10 amu are assigned to the one-photon transition, A 1Π ( v ′=2)– X 1Σ + (v″=0) , in 11BH and 10BH. Cation production at these wavelengths requires three photons. This signal must therefore reflect resonant one-photon absorption followed by two-photon ionization in a (1+2)-photon process. This work represents the first observation of the well-characterized A 1Π – X 1Σ + system in ionization spectroscopy and the first measurement of line positions in the A 1Π v=2 state for 10BH.

Ion irradiation of rare-earth- and yttrium-titanate-pyrochlores

Pyrochlore, A 1–2B 2O 6(O,OH,F) 0–1, is an actinide-bearing phase in Synroc, a polyphase ceramic proposed for the immobilization of high level nuclear waste. Structural damage due to alpha-decay events can significantly affect the chemical and physical stability of the nuclear waste form. Pyrochlore can effectively incorporate a variety of actinides into its structure. Four titanate pyrochlores were synthesized with compositions of Gd 2Ti 2O 7, Sm 2Ti 2O 7, Eu 2Ti 2O 7 and Y 2Ti 2O 2. These samples were irradiated with 1 MeV Kr + in order to simulate alpha-decay damage and were observed by in situ electron microscopy. Irradiations were conducted from 25 K to 1023 K. At room temperature, Gd-, Sm- and Eu-pyrochlores amorphized at a dose of ∼2×10 14 ions/cm 2 (∼0.5 dpa) and Y-pyrochlore amorphized at 4×10 14 ions/cm 2 (∼0.8 dpa). The amorphization dose became higher at elevated temperatures with different rates of increase for each composition. The critical temperatures for amorphization are ∼1100 K for Gd-, Sm-, Eu-pyrochlore and ∼780 K for Y-pyrochlore. The rare-earth-pyrochlores are more susceptible to amorphization and have higher critical temperatures than Y-pyrochlore. The difference in amorphization dose and critical temperature is attributed to the different cascade sizes caused by the different cation masses of the target. Based on a model of cascade quenching, the larger cascade is related to a lower amorphization dose and higher critical temperature. The irradiated materials were studied by electron diffraction and high-resolution electron microscopy. All the pyrochlores transformed to a fluorite substructure prior to the completion of amorphization of the observed regions. This transformation was caused by the disordering between cations and between oxygen and oxygen vacancies. The concurrence of cation disordering with amorphization suggests the partial recrystallization of the displacement cascades. Isolated cascade damage regions were observed by high-resolution electron microscopy, and the cation disordering was associated with the damaged regions.

Influence of deviations from stoichiometry on the ir spectra of yttrium-iron garnet crystals

We have measured the absorption coefficients in the IR range as well as the cathodoluminescence spectra and also evaluated the content of the basic (Y, Fe, O) and impurity (Ba, Mn, Pt, Bi, Sm, V, Pb) elements of yttrium-iron garnet Y3Fe5O12 (YIG) cut along different crystallographic planes. We show that Ba ions, as the main uncontrolled impurity, replace Y ions in varying degrees, thus exerting an inadequate influence on the absorption coefficients α (λ=1.3 µm) for samples of sections (110) and (111). It is established that Ba impurity in the concentration range 0.8 to 1.5 wt.% reduces α to a minimum, which is apparently due to suppression of the process of generation of dislocations. The quality of the YIG crystals is most fully characterized by the ratio of the sum of the masses of cations to the sum of anions.