Ionic Model Calculations Research Articles

The behavior of nickel isotopes during mantle melting

Mantle-derived mafic rocks show relatively large variations in nickel (Ni) isotopes and mostly isotopically light compared to the bulk silicate Earth (BSE). Whether this signature is due to the source heterogeneity or controlled by melting processes has been a debatable issue. Here, we analyzed Ni isotopic compositions of 18 intraplate basalts from the Sabzevar region, northern Iran and 16 serpentinized peridotites from Cyprus and South China. The Sabzevar basalts were likely sourced from a sulfur-free/barren mantle domain with recycled pyroxenites involved, manifested by their high Cu contents (127–265 ppm), FeT/Mn (58.2–77.4) and Zn/FeT ratios (11.9–16.4). The Ni isotopic compositions of the Sabzevar basalts (average δ60/58Ni = +0.15 ± 0.08 ‰; 2SD) are slightly heavier than the BSE value (average δ60/58Ni = +0.11 ± 0.06 ‰; 2SD), consistent with equilibrium Ni isotope fractionation during mantle silicate melting as predicted by ionic model calculations. Our new data of serpentinized peridotites (average δ60/58Ni = +0.16 ± 0.06 ‰; 2SD), together with previously reported data for oceanic sediments and metabasalts, suggest that recycled lithologies have mantle-like or relatively heavy Ni isotopic compositions. Thus, the isotopically light Ni in mafic rocks is unlikely to be caused by crustal recycling-induced mantle heterogeneity. Rather, the light Ni isotopic signature is caused by the dissolution of recycled sulfides into the mantle melts. We suggest two sulfide dissolution models (“dissolve and go” and “dissolve and equilibrium”) to describe the δ60/58Ni and Cu systematics in terrestrial basalts. In both models, the initial sulfide content (Sinitial) and oxygen fugacity (fO2) exert a major control on Ni isotopic compositions of resulting melts. These two parameters vary among different geological settings. Basalts derived from mantle sources with high Sinitial and fO2 are characterized by light Ni isotopic compositions, whereas basalts sourced from sulfur-free/barren and reduced mantle domains are likely characterized by heavy Ni isotopic compositions, aligning with the characteristic observed in natural samples.

Combined DFT and ionic model computational study of the effect of alkali metal cations on the structure, bonding and properties of molten cryolites, M3AlF6 (M = li, Na, K, Rb, and Cs)

ABSTRACT Ionic melts, in the form of ionic liquids and molten salts, are important in many technological aspects such as metal production and energy applications. Cryolite melts constitute an important family especially for the industrial production of Al. The present computational study aims to analyse the effect of different cations on the structure and properties of Al (III) fluorocomplexes in cryolite melts. Cation effects are discussed as the ion pair interactions due to alkali metal cations of cryolite compounds M3AlF6 with M= Li, Na, K, Rb, or Cs for various microclusters using ionic interaction model (IM) and DFT calculations. DFT results for different ion complexes are compared with the energy calculations using a pseudoclassical model for isolated clusters. QTAIM and ELF analyses were performed to understand the nature of interactions in detail. A link between open-shell interactions and decreased ionic conductivity is proposed within the series of K, Rb, and Cs. Environmental effects, such as temperature and presence of other ions, are investigated in detail by DFT analysis.

Structure and bonding in cryolitic melts a combined study by density functional theory and ionic model calculations

Present study aims to analyze the nature of the bonding of ion pairs and formation of Al(III) fluorocomplexes by discussing the detailed ion pair interactions for various microclusters on AlF3/NaF solutions (cryolitic melts). Using a comparative study between the density functional theory and an interionic force-field model calculations developed in our group, the structure of neutral micro clusters in cryolitic melts are analyzed to reveal their bonding characteristics of the ion pairs. Quantum Theory of Atoms in Molecules (QTAIM) analyses were perfomed in order to understand the molecular or ionic interactions both in vacuo and in dielectric continuum. This study provides detailed information about the local structure in cryolitic melts in terms of the bonding interactions between the ions.

Rational Design of 3d Transition-Metal Compounds for Thermoelectric Properties by Using Periodic Trends in Electron-Correlation Modulation.

The electronic structures in solid-state transition-metal compounds can be represented by two parameters: the charge-transfer energy (Δ), which is the energy difference between the p-band of an anion and an upper Hubbard band contributed by transition-metal d-orbitals, and the onsite Coulomb repulsion energy (U), which represents the energy difference between lower and upper Hubbard bands composed of split d-orbitals in transition metals. These parameters can facilitate the classification of various types of electronic structures. In this study, the dependences of anion species (N3-, P3-, As3-, O2-, S2-, Se2-, Te2-, F-, Cl-, Br-, and I-) on Δ and U of 566 different binary and ternary 3d transition-metal compounds were investigated using ionic-model calculations. We were able to identify the systematic chemical trends in the variations in Δ and U values with the anion species of 11 different families of 3d transition-metal compounds in a comprehensive manner. The effective use of Δ-U diagrams given here, to facilitate the discovery and development of functional compounds, was demonstrated on thermoelectric compounds by classifying the thermoelectric properties of 3d transition-metal compounds and by predicting unrealized high-performance thermoelectric compounds.

Zinc isotope fractionation between Cr-spinel and olivine and its implications for chromite crystallization during magma differentiation

We report the first zinc isotope data (expressed as δ66Zn relative to the JMC-Lyon standard) for chromian spinels (Cr-spinels) and coexisting olivines in oceanic peridotites. All spinel-olivine pairs fall on the 1:1 fractionation line in the diagram of δ66Znspinel versus δ66Znolivine, suggesting equilibrium isotope fractionation. Cr-spinels are always isotopically lighter than coexisting olivines (Δ66Znspinel-olivine = δ66Znspinel − δ66Znolivine = −0.50‰ to −0.33‰; n = 13), which is opposite to the positive Zn isotope fractionation between Al-spinel and olivine observed in cratonic peridotites. The “inverse” Zn isotope fractionation between Cr-spinel and olivine is unlikely to have been caused by low-temperature alteration of the oceanic peridotites, given the lack of correlation between Δ66Znspinel-olivine values and chemical indices of serpentinization and weathering (e.g., LOIs, MgO/SiO2). Ionic model calculation indicates that even considering that Zn occurs at both tetrahedral and octahedral sites in the crystal lattice of spinel, the magnitude of equilibrium fractionation is still inconsistent with the observed Zn isotope fractionation between Cr-spinel and olivine. We suggest a “chemical effect” in which the ZnO bond length (tetrahedral site) in spinel increases when Cr substitutes Al in octahedral site, which is corroborated by the striking negative correlation of δ66Zn with Cr# [molar Cr3+/(Cr3+ + Al)] in natural spinels. Therefore, Zn isotopic compositions of natural spinels can be highly variable depending on their chemical compositions.During magma differentiation, zinc is moderately incompatible in silicate minerals (olivine and pyroxene) but highly compatible in Cr-spinels/chromites that have Zn contents tens of times higher than those of basaltic melts. Given its light Zn isotopic composition, chromite crystallization–if any–can evidently elevate δ66Zn and lower Zn contents of the residual melts. Lunar mare basalts are typically characterized by higher δ66Zn and lower Zn contents relative to terrestrial basalts, but modelling suggests that chromite crystallization during magmatic differentiation is unlikely to account for Zn isotopic and elemental data of lunar mare basalts. Global ocean island basalts (OIBs) and some intraplate alkali basalts have systematically higher δ66Zn and higher Zn contents than those of the normal mantle-derived melts (e.g., mid-ocean ridge basalts; MORBs), which contradicts with a chromite crystallization model. Instead, such signatures can reflect recycling of surface carbonates into the Earth’s deep mantle, reinforcing the application of zinc isotopes as a tracer of deep carbonate recycling.

Observation of the 4f ground-state symmetry in strongly correlated cubic Pr compounds probed by linearly polarized 3d core-level photoemission spectroscopy

We report the core-level photoemission study of cubic PrBe13, PrIr2Zn20 and PrB6 using linearly polarized hard X-ray. We have successfully observed linear dichroism (LD) in Pr3+ 3d core-level photoemission spectra reflecting the 4f ground-state symmetry for all the compounds. The observed LDs and polarization-dependent spectra are reproduced by ionic-model calculations including the full multiplet theory and the local crystalline electric field (CEF) splitting. We have confirmed that LDs in Pr3+ 3d core-level photoemission spectra are able to determine unambiguously the Pr3+ 4f ground-state symmetry.

Electronic Structure of Copper Antimony Using Compton Scattering Technique

In this paper we present the first ever measured experimental electron momentum density of Cu2Sb at an intermediate resolution (0.6 a.u.) using 59.54 keV 241Am Compton spectrometer. The measurements are compared with the theoretical Compton profiles using density function theory (DFT) within a linear combination of an atomic orbitals (LCAO) method. In DFT calculation, Perdew-Burke-Ernzerhof (PBE) scheme is employed to treat correlation whereas exchange is included by following the Becke scheme. It is seen that various approximations within LCAO-DFT show relatively better agreement with the experimental Compton data. Ionic model calculations for a number of configurations (Cu+x/2)2(Sb-x) (0.0≤x≤2.0) are also performed utilizing free atom profiles, the ionic model suggests transfer of 2.0 electrons per Cu atom from 4s state to 5p state of Sb.

Crystal chemistry and thermal behavior of La doped (U, Th)O2

X-ray diffraction, chemical and thermal studies of [(U0.2Th0.8)1-yLay]O2+x (LUTL) and [(U0.3Th0.7)1-yLay]O2+x (UTL); compounds (where y ≤ 0.4) were carried out. These compounds were synthesized by gel combustion method followed by heating in reduced atmospheres at 1673 K. To co-relate lattice parameters with metal and oxygen concentrations, reduced oxides were heated in Ar, CO2 and air atmospheres. Retention of FCC phase was confirmed in all mixed oxides with y ≤ 0.4. The cubic lattice parameters could be expressed in a linear equation of x and y as:a (Ǻ) = 5.5709 − 0.187 x + 0.032 y; [x < 0 and 0 ≤ y ≤ 0.40] for LUTL anda (Ǻ) = 5.5580 − 0.26 x + 0.015 y; [x < 0 and 0 ≤ y ≤ 0.36] for UTL.Oxidation studies and simple ionic model calculations suggested that uranium is predominantly present as a mixture of +5 and + 6 states when La/U ratio ∼2. Oxidation kinetics of mixed oxides was studied by non-isothermal method using thermogravimetry and was found to be a diffusion controlled reaction. High temperature X-ray diffraction studies of LUTL and UTL mixed oxides showed positive thermal expansion in the temperature range of 298–1273 K and % expansion increases with La concentration.

High-Temperature Monoclinic Cc Phase with Reduced c/a Ratio in Bi-based Perovskite Compound Bi2ZnTi1–xMnxO6

Monoclinic phases with Cm, Pm, and Cc space groups are indispensable to understand the high performance of electromechanical properties at the morphotropic phase boundary (MPB) of lead-based perovskite oxides Pb(ZrxTi1-x)O3 (PZT), [Pb(Mg1/3Nb2/3)O3]1-x-(PbTiO3)x (PMN-PT), and [Pb(Zn1/3Nb2/3)O3]1-x-(PbTiO3)x (PZN-PT). Here, a nearly single monoclinic phase with space group Cc was observed in the Bi-based lead-free perovskite compound Bi2ZnTi1-xMnxO6 at x = 0.4. This phase was the same as the low-temperature phase of the MPB composition of PZT but existed at a much higher temperature. Despite the reduced pseudo c/a ratio of 1.065, which is the same as that of PbTiO3 at room temperature, ionic model calculation based on the Rietveld refinement data indicated the polarization of Bi2ZnTi0.6Mn0.4O6 is 95.8 μC/cm(2). The tilting and significant anisotropic distortion of the octahedron were found to cause the c/a ratio to reduce. Accordingly, the effective piezoelectric constant d33 of Bi2ZnTi0.6Mn0.4O6 thin film was found to be 12 pm/V.

Electronic Structure of Copper Antimony Using Compton Scattering Technique

In this paper we present the first ever measured experimental electron momentum density of Cu2Sb at an intermediate resolution (0.6 a.u.) using 59.54 keV 241Am Compton spectrometer. The measurements are compared with the theoretical Compton profiles using density function theory (DFT) within a linear combination of an atomic orbitals (LCAO) method. In DFT calculation, Perdew-Burke-Ernzerhof (PBE) scheme is employed to treat correlation whereas exchange is included by following the Becke scheme. It is seen that various approximations within LCAO-DFT show relatively better agreement with the experimental Compton data. Ionic model calculations for a number of configurations (Cu+x/2)2(Sb-x) (0.0≤x≤2.0) are also performed utilizing free atom profiles, the ionic model suggests transfer of 2.0 electrons per Cu atom from 4s state to 5p state of Sb.

Self-doping processes between planes and chains in the metal-to-superconductor transition of YBa2Cu3O6.9.

The interplay between the quasi 1-dimensional CuO-chains and the 2-dimensional CuO2 planes of YBa2Cu3O6+x (YBCO) has been in focus for a long time. Although the CuO-chains are known to be important as charge reservoirs that enable superconductivity for a range of oxygen doping levels in YBCO, the understanding of the dynamics of its temperature-driven metal-superconductor transition (MST) remains a challenge. We present a combined study using x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) revealing how a reconstruction of the apical O(4)-derived interplanar orbitals during the MST of optimally doped YBCO leads to substantial hole-transfer from the chains into the planes, i.e. self-doping. Our ionic model calculations show that localized divalent charge-transfer configurations are expected to be abundant in the chains of YBCO. While these indeed appear in the RIXS spectra from YBCO in the normal, metallic, state, they are largely suppressed in the superconducting state and, instead, signatures of Cu trivalent charge-transfer configurations in the planes become enhanced. In the quest for understanding the fundamental mechanism for high-Tc-superconductivity (HTSC) in perovskite cuprate materials, the observation of such an interplanar self-doping process in YBCO opens a unique novel channel for studying the dynamics of HTSC.

A study of electron momentum density distribution in Al2O3 ceramic

A study of electron momentum density distribution in α-Al2O3 ceramic using Compton spectroscopy is presented in this work. Measurements have been carried out using 59.54 keV gamma-rays emanating from an Am241 source. Calculations have been performed on the basis of the ab-initio linear combination of atomic orbitals (LCAO) method embodied in the CRYSTAL code. The correlation scheme proposed by Perdew–Burke–Ernzerhof was adopted. The exchange was treated following the Becke scheme. The Hartree–Fock and hybrid schemes were also applied to the compound. All the schemes yielded results that are in good agreement with the measurements. The agreement with experiment is, however, better with the hybrid B3LYP (Lee–Yang–Parr) scheme. Ionic model calculations for a number of configurations of (Al+x)2(O−2x/3)3 (2.75⩽x⩽3 in steps of 0.125) were also performed utilizing free atom profiles. The ionic model suggests transfer of 2.875 electrons from the valence sp state of Al to the p state of O.

Electron momentum density distribution in Cd 3P 2

A study of electron momentum density distribution in Cd 3P 2 is reported in this work. The measurement of Compton profile is carried out on a polycrystalline sample using 59.54 keV gamma-rays emanating from an 241Am radioisotope. The theoretical calculations are performed using linear combination of atomic orbitals method following the Hartree–Fock and a posteriori density functional theories. The spherically averaged theoretical Compton profiles are in good agreement with the measurement. The best agreement is, however, shown by the Hartree–Fock scheme. Simple ionic model calculations for a number of configurations ( Cd + x ) 3 ( P − 3 x / 2 ) 2 ( 0.0 ⩽ x ⩽ 2.0 in step of 0.2) are also performed utilizing free atom profiles. The ionic model supports transfer of 2.0 electrons per Cd atom from 5 s state to 3 p state of P.

Ab-initio determination of X-ray structure factors and the Compton profiles of CdO

X-ray structure factors and Compton profiles of CdO are presented in this work. The theoretical calculations are performed employing the first-principles linear combination of atomic orbitals (LCAO) method using the CRYSTAL code. The computations are made considering the Perdew–Burke–Ernzerhof (PBE) correlation energy functional and Becke's ansatz for the exchange. The computed X-ray structure factors for B1 structure are compared with the available experimental data. To compare the averaged theoretical Compton profile, first ever measurement on polycrystalline CdO is reported using 5Ci 241Am Compton spectrometer. The ionic model calculations have been used to estimate charge transfer in CdO. The agreement is, however, better with the LCAO calculation. The first-principles calculations of equilibrium lattice constants, bulk moduli and its pressure derivative of competing B1 and B2 phases of CdO are also reported and compared with the available results. The computed transition pressure for B1 → B2 structural phase transition is in good agreement with the experimental findings. Moreover, the electronic band structures show that B1 phase has indirect band gap of 0.43 eV in reasonable agreement with the experiments and B2 phase exhibits negative band gap of 0.9 eV.

Electron momentum distribution in SnS

AbstractA study of electron momentum density distribution in SnS by means of Compton profiles is presented. The measurement on polycrystalline sample of SnS is performed employing 59.54 keV gamma‐rays emanating from an Am241 radioisotope. The calculations are performed on the basis of density‐functional theory based ab‐initio linear combination of atomic orbitals method embodied in the CRYSTAL program. The correlation scheme proposed by von Barth and Hedin is adopted. The generalized gradient approximation proposed by Perdew and Wang is also considered to treat the correlation. The exchange is treated following the Becke scheme. Both the correlation schemes are in good agreement with the measurement. The better agreement with experimental result is, however, observed with the von Barth and Hedin correlation that also gives lower ground‐state energy than the Perdew–Wang generalized gradient approximation. Ionic model calculations for a number of configurations of Sn+xS−x (0.0 ≤ x ≤ 2) are also performed utilizing free‐atom profiles. The ionic model suggests transfer of 2.0 electrons from the valence 5p state of Sn to the 3p state of S.

Modeling phase stability in [formula omitted] perovskites

Order-disorder phenomena on the simple-cubic B-site sublattice in A(B 1 3 B′ 2 3 )O 3 perovskites is examined. A simple cubic groundstate analysis in the cube approximation reveals that this approximation is inadequate for A(B 1 3 B′ 2 3 )O 3 perovskites, because it cannot predict a common experimentally-observed [111]superstructure. A partial vertex enumeration technique is used to demonstrate that a cube + linear triplet approximation is sufficient. First-principles calculations were performed for Ba(Zn 1 3 Ta 2 3 )O 3 (BZT) and Pb(Mg 1 3 Nb 2 3 )O 3 (PMN), two technologically interesting materials, in an effort to construct generalized Ising model Hamiltonians to enable simulations of these materials. Both ionic model (SSCAD) and pseudopotential (PP) calculations were done, enumerating the relative energies of a series of B-site superstructures. Structural hierarchies are reasonable and predict the [111] groundstate for both BZT and PMN, despite the fact that it is not observed in the latter. The pseudopotential results also indicate the possibility of metal-insulator transitions in BZT as a function of B-site configuration. The latter result indicates a possible explanation for the curious dielectric properties of non-isovalent mixed B-site materials. Differences were found between the SSCAD and PP calculations for BZT; these indicate the SSCAD calculations are probably sufficient for low-energy excitations, but inaccurate for high-energy structures.

NMR study on ionic conduction in silver and alkali halides

The data of the temperature dependence of nuclear quadrupole relaxation rate, 1 T 1 in silver and sodium halides with the rocksalt structure are compared with an ionic model calculation, in which the degree of covalency is estimated. The results are discussed in connection with the ionicity of A N B 8 − N binary compounds.

Modeling Phase Stability in a(B1/3B'2/3)O3 Perovskites

AbstractOrder-disorder phenomena on the simple-cubic B-site sublattice in A(B1/3B'2/3)O3 perovskites is examined. A simple cubic groundstate analysis in the cube approximation reveals that this approximation is inadequate for A(B1/3B'2/3)O3 perovskites, because it cannot predict a common experimentally-observed [111] superstructure. A partial vertex enumeration technique is used to demonstrate that a 12 interaction subset of the cube + linear triplet approximation is sufficient. First-principles calculations were performed for Ba(Zn1/3Ta2/3)O3 (BZT) and Pb(Mg1/3Nb2/3)O3 (PMN), two technologically interesting materials, in an effort to construct generalized Ising model Hamiltonians to enable simulations of these materials. Both ionic model (SSCAD) and pseudopotential (PP) calculations were done, enumerating the relative energies of a series of B-site superstructures. Structural hierarchies are reasonble and predict the [111] groundstate for both BZT and PMN, despite the fact that it is not observed in the latter. The pseudopotential results also indicate the possibility of metal-insulator transitions in BZT as a function of B-site configuration.

Elastic constants and Debye temperature of Y 1Ba 2Cu 3O x: effect of oxygen content

Using ultrasonic methods, we measured the elastic constants of polycrystalline Y 1Ba 2Cu 3O x between 295 and 4 K. For a single specimen, using vacuum annealing and oxygen annealing, we varied the oxygen content in four steps from x=6.2 to x=6.9. Elastic stiffnesses that depend mainly on shear modes increase monotonically with increasing oxygen content. Stiffnesses that depend on dilatation modes increase up to about x=6.7 and then decrease. The elastic Debye temperature, which depends mainly on shear modes, increases monotonically, in agreement with the specific-heat Debye temperature. An ionic-model calculation for the bulk modulus and Debye temperature predicts a monotonic increase for both. We conjecture that the irregular oxygen-content dependence of the dilatation-mode-related elastic constants arises from changes in copper-oxygen valences.

Mass-spectrometric study of the formation, evaporation, and structural properties of doubly charged MgO clusters.

Doubly charged (MgO${)}_{\mathit{n}}$${\mathrm{Mg}}^{2+}$ (n=4--172) and (MgO${)}_{\mathit{n}}$${\mathrm{Mg}}_{2}^{2+}$ (n=12--24) clusters were produced in a gas-aggregation source and studied by using laser-ionization time-of-flight mass spectrometry. The mass spectrum exhibits an interesting dependence on the source conditions, such that it can be changed from one comprised of singly charged clusters to one comprised almost entirely of doubly charged clusters, simply by changing the flow rate of the carrier gas. The abundance of patterns of (MgO${)}_{\mathit{n}}$${\mathrm{Mg}}^{2+}$ clusters shows that the clusters have cubic structures resembling pieces of the MgO fcc crystal lattice, with the most stable structures being cuboids, and cuboids with an O-atom vacancy or complete terrace. The abundances of (MgO${)}_{\mathit{n}}$${\mathrm{Mg}}_{2}^{2+}$ clusters can also be explained in terms of cubic structures, but in this case the O-atom vacancies may be occupied by one or two excess electrons, analogous to a solid-state F center. Simple ionic-model calculations of the structures and relative stabilities of (MgO${)}_{\mathit{n}}$${\mathrm{Mg}}^{2+}$ clusters are in good agreement with those inferred from the mass spectra. The (MgO${)}_{\mathit{n}}$${\mathrm{Mg}}^{2+}$ clusters evaporate primarily by losing magnesium and oxygen in equal amounts, similar to the congruent vaporization of solid MgO, yielding clusters of the same series. The mechanism of evaporation is probably a stepwise one in which the movement of atoms or molecules from corners, kinks, and ledges into an adsorbed layer exerts at least partial control over the evaporation rate. At small sizes the doubly charged clusters also appear to undergo Coulomb explosion, in which they fragment to form (MgO${)}_{\mathit{n}}^{+}$ and (MgO${)}_{\mathit{n}}$${\mathrm{Mg}}^{+}$ clusters.