Analysis of the charge transfer mechanisms responsible for the current-voltage characteristics of Ca<Subscript>4</Subscript>Ga<Subscript>2</Subscript>S<Subscript>7</Subscript>: Eu<Superscript>3+</Superscript> single crystals

The current-voltage characteristics of Ca₄Ga₂S₇: Eu³⁺ single crystals are measured for the first time, and the processes affecting these characteristics are analyzed theoretically. It is demonstrated that Ca₄Ga₂S₇: Eu³⁺ single crystals are high-resistance semiconductors with a resistivity of ～10⁹ Ω cm and a relative permittivity of 10.55. The electrical properties of the studied materials are governed by traps with activation energies of 0.13 and 0.19 eV and a density ranging from 9.5×10¹⁴ to 2.7×10¹⁵ cm^?3. The one-carrier injection is observed in weak electric fields. In electric fields with a strength of more than 4×10³ V/cm, traps undergo thermal field ionization according to the Pool-Frenkel mechanism. At low temperatures and strong fields (160 K and 5×10⁴ V/cm), the electric current is most likely due to hopping conduction by charge carriers over local levels in the band gap in the vicinity of the Fermi level.     

Structural equilibrium (S=0) ⇄ (S=1)and inversion of the configuration of the seven-membered saturated metal-containing ring in four-coordinate pyrazolealdiminate metal chelates of nickel(II) based on tetradentate ligands

¹H and¹³C NMR, x-ray structural analysis, and magnetic moment measurements have shown that in 5-thio(seleno)pyrazolealdiminate complexes of nickel(II) based on tetradentate ligands containing the fragment, with n=2, flattening of the chelate unit takes place in solution and in the solid state. A similar structure in which the diamine metal-containing ring has the twist-chair conformation is observed for the crystals of the complexes with n=4. For the complexes with n=4 in solution at a temperature below –50°C, rapid (on the NMR time scale) interconversion of the flattened (P) (S=0) and pseudotetrahedral (T) (S=1) structures is observed, not accompanied by inversion of the tetrahedral configuration of the metal atom. At temperatures above –50°C, in addition to the low-barrier reactions (T) (P), conversion of the seven-membered saturated metal-containing ring and inversion of the tetrahedral configuration of the Ni atom with activation barriers of 48–51 kJ/mole are observed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 327–335, February, 1990.     

Catalytic activity of tetracoordinated stereochemically flexible Ni(II) bis(5-thiopyrazol-4-aldiminates) in the dimerization of propylene

The catalytic activity of Ni(II) bis-(5-thiopyrazol-4-aldiminates) was found to be related to the stereochemical flexibility of these compounds in the dimerization of propylene. The propylene conversion decreases with decreasing stereochemical flexibility of the complexes resulting from an increase in the bulk of the substituent at the coordinated nitrogen atom of the NiN₂S₂ chelate ring.Institute of Inorganic and Physical Chemistry, Academy of Sciences of Azerbaidjan, 370143 Baku. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2667–2670, November, 1992.     

Physicochemical Aspects of Development of Multicomponent Chalcogenide Phases Having the Tl<Subscript>5</Subscript>Te<Subscript>3</Subscript> Structure: A Review

The literature data on ternary structural analogues of the compound Tl₅Te₃ and multicomponent phases based on them are systematized. This class of inorganic substances is of considerable scientific and practical interest as promising functional materials having thermoelectric, optical, and magnetic properties, as well as topologically protected surface states and superconductivity. The focus of the survey is on phase equilibria in ternary and more complex systems where structural analogues of Tl₅Te₃ are formed. Crystalstructure features, thermodynamic and some physical properties of these compounds and phases of variable composition are considered.     

Thermodynamic Study of the Ag–Sb–Se System by the EMF Method with Ag4RbI5 Solid Electrolyte

Russian Journal of Electrochemistry - The results of studying the Ag–Sb–Se system by measuring the electromotive force (EMF) of concentration cells with the Ag4RbI5 solid electrolyte...     

Phase effects at second harmonic generation of powerful laser radiation in noncentrosymmetrical media

There has been developed the theory of second harmonic generation of the intensive laser fields in the existence of both quadratic and cubic polarization in medium in the constant-intensity approximation accounting for the reverse effect of the excited wave on the exciting one and simultaneously allowing us to take into account phase mismatch and the damping of all the interacting waves. It is shown that the changes of pump intensity through self-phase and cross-phase modulation processes effect optimum phase relationship between interacting waves, the change of the spatial beating period. The conditions of compensating undesirable phase shifts between interacting waves have been determined, the analytical expressions for calculation of optimum values of phase mismatch, length of noncentrosymmetrical medium and the spatial beating period are offered. It is shown that in the absence of linear phase mismatch with an increase of basic radiation intensity the spatial beating period is being reduced. The numerous analysis has been made of frequency doubling process efficiency for KDP and LiNbO₃ crystals.