Electronic structures,chemical bonding,and defect formation in mixed cyanoferrates M<Subscript>2</Subscript>Cu[Fe(CN)<Subscript>6</Subscript>] (M = Na,K, Rb,and Cs)

The effect of the alkali metal nature on the electronic structures and chemical bonding in mixed cyanoferrates M₂Cu[Fe(CN)₆] (M = Na, K, Rb, and Cs) was studied by ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method (in the spin-polarized implementation) and the extended Hückel molecular orbital (EHMO) method. It was found that the X-ray photoelectron spectra of the ferrimagnetic compounds Na₂Cu[Fe(CN)₆] (I), K₂Cu[Fe(CN)₆] (II), Rb₂Cu[Fe(CN)₆] (III), and Cs₂Cu[Fe(CN)₆] (IV) are similar. The magnetic moments on Cu²⁺ and iron ions remain virtually constant in compounds I–IV (μ(Cu) = 0.9 μ_B, μ(Fe) < ?0.06 μ_B). Analyses of the electron density maps and the bond overlap populations showed that the cubic frameworks of cyanoferrates are built from stable fragments ?-Fe-C≡N-Cu-?. The bond strength in these fragments decreases substantially in the order C-N → Fe-C → Cu-N and only slight in the order IV → III → II → I. The calculated total energies of the cyanoferrates Cs_2?x Cu[Fe(CN)₆], CsHCu[Fe(CN)₆], and NaHCu[Fe(CN)₆] for different concentrations and configurations of defects (cesium vacanices and hydrogen substitution defects) suggest mutual repulsion of defects. This repulsion is responsible for the experimentally observed lowering of the ionic conductivity with an increase in the defect concentration in the mixed cyanoferrates.     

Influence of Cation Impurities and Both Cation and Anion Nonstoichiometry on Aluminum Oxide Energy Gap Width

JETP Letters - Using the coherent potential approximation, the electronic structure of α- $${\text{A}}{{{\text{l}}}_{2}}{{{\text{O}}}_{3}}$$ (corundum) with various concentrations of mono and...     

Kinetic effects in an La0.8Ba0.2MnO3 single crystal

Results are presented of a complex study of the magnetic and resistive properties, the Hall effect, the thermal emf, and the longitudinal Nernst-Ettingshausen effect of an La_0.8Ba_0.2MnO₃ single crystal at temperatures between 77 and 400 K. A maximum was observed near the Curie temperature T _c on the temperature dependences of the resistivity, the thermal emf, and the normal Hall coefficient. It was established that the Hall mobility remains constant near T _c. It is shown that these anomalies in the kinetic properties are attributable to a change in the position of the mobility edge relative to the Fermi level. A semiphenomenological theory is put forward to quantitatively describe the temperature and magnetic-field dependences of the resistivity and thermal emf of lanthanum manganites near the phase-transition temperature.     

Cerium influence on the thermal properties and structure of high-alkaline borosilicate glasses

Journal of Thermal Analysis and Calorimetry - The influence of cerium oxide on the thermal properties and the glass structure has been studied for the...     

Elastic Properties of La0.7 – yPryCa0.3MnO3 Single Crystals (0 ≤ y ≤ 0.3)

Physics of the Solid State - Temperature dependences of longitudinal sound wave velocities and internal friction of ferromagnetic La0.7&nbsp;–&nbsp;yPryCa0.3MnO3 single crystals (0...     

Giant thermal hysteresis in lanthanum manganites

The giant thermal hysteresis of the longitudinal sound velocity and internal friction turns out to be a specific feature of the orthorhombic-to-rhombohedral structural transition in La_1−xSr_xMnO₃ and La_1−xBa_xMnO₃ manganites. The mixture of the orthorhombic and rhombohedral phases can exist far beyond the thermal hysteresis loop as it is observed in magnetization or resistivity experiment. This means that in the CMR manganites, the boundary between the crystal phases is fuzzy.     

Electronic structure and properties of strontium ferrite Sr3Fe2O6

The electronic structure of strontium ferrite Sr₃Fe₂O₆ was calculated using the tight-binding linear muffin-tin orbital method (TB LMTO) in the local spin density approximation of density functional theory with Coulomb correlations correction (LSDA+U). The semiconducting character of the spectrum with charge transfer energy gap of 1.82 eV was obtained in reasonably good agreement with experimental data. The iron ions are found to be in the high spin state. The calculated value of the local spin magnetic moment of Fe³⁺ ion is 3.94 μ_B which is not typical for trivalent iron ion in the high spin state. It is shown that the strong hybridization between Fe3d and O2p orbitals favors the d⁶ L configuration of Fe³⁺ ion, where L is a hole in the oxygen p shell. The mechanism of oxygen transport in ferrite is discussed basing on the total energy calculations of the different spatial configurations of oxygen vacancies.     

Mercury(II) and silver(I) receptors based on tetrathiacalix[4]arene hydrazones

The extraction ability of phenyl hydrazone derivatives of cone- and 1,3-alternate tetrathiacalix[4]arenes towards to some alkali, alkaline earth, transition and heavy metal ions has been investigated by picrate extraction method. The synthesized cone-tetrathiacalix[4]arene hydrazones show a high efficiency coupled with an excellent selectivity towards for Ag⁺ and Hg²⁺ ions. The stoichiometry of complexes and the extraction constants have been determined. The influence of calix[4]arene platform’s structure and the electron donor substituents in phenyl fragments on the extraction efficiency has been discussed.     

Defect clusterization and transport properties of oxide and fluoride ionic conductors with fluorite structure: Quantum-chemical approach

Systematic studies of the effect of point defects on the electronic structure, chemical bond, and ionic conduction of classical ionic conductors MeF₂ (Me=Ca, Sr, Ba, Pb), ZrO₂-CaO, ZrO₂-Y₂O₃, and δ-Bi₂O₃ are carried out using the nonempirical LMTO method in the tight-binding approximation and using Hückel’s semiempirical method. The energies of formation and interaction of anti-Frenkel defects are calculated. The effect of defect clusterization in these compounds is detected. This effect is responsible for the emergence of the superionic state and anomalous physicochemical properties of the given solid electrolytes. The nature of instability of the fluorite structure is studied, and methods of its stabilization are proposed. The mechanisms and energetics of ionic transport in oxide and fluoride conductors with fluorite structure are investigated.     

Elastic properties of lanthanum manganites

We give a brief overview of the data on elastic properties of the CMR manganites published during last decade. The main emphasis is put on the results obtained for single crystals.