Alexey Baranov

Thermodynamic properties and neutron diffraction studies of silver ferrite AgFeO2

We present thermodynamic and neutron scattering data on silver ferrite AgFeO(2). The data imply that strong magnetic frustration Θ/T(N)∼10 and magnetic ordering arise via two successive phase transitions at T(2) = 7 K and T(1) = 16 K. At T<T(2), two metamagnetic phase transitions at B(1)∼14 T and B(2)∼30 T can be identified through the change of slope in the magnetization curve measured up to 53 T. These transitions roughly correspond to an eighth and a quarter of the saturation magnetizations. Unlike for the classical delafossite CuFeO(2), the wavevector of the magnetic structure is independent of temperature both at T<T(2) and at T(2)<T<T(1).

The structure and bonding of Ni3Sn

Abstract The electronic structure of Ni3Sn was calculated at ab initio levels for the crystal structure of the low-temperature modification of Ni3Sn refined upon data of single-crystal X-ray diffractometry (P63/mmc, a=5.2950(7), c=4.247(1) A, R=0.0288). The calculations were made with the use of fixed Gaussian (CRYSTAL98 software) and energy-dependent (Stuttgart TB-LMTO-ASA software) basis sets. Difference electron charge density maps were analysed and compared with that of a hypothetical hcp Ni in order to understand bonding in Ni3Sn. It was found that bonding in Ni3Sn has multicentre character with Ni–Sn interaction stronger than Ni–Ni one.

Crystal and electronic structure of Ni3Bi2S2 (parkerite)

The crystal structure of parkerite, Ni3Bi2S2, was studied by single-crystal X-ray diffraction analysis and refined. The single crystal was prepared by the method of chemical transport reactions. The electronic structure of Ni3Bi2S2 was calculated by the extended Hückel and DFT--LMTO--ASA methods. Substantial delocalization of electrons in the vicinity of the Fermi level and the presence of the strong Ni--S and Ni--Bi bonds were revealed. The Ni--Ni bonds are weak, which is in agreement with the X-ray diffraction data.

Synthesis and the crystal structure of [Hg6As4](InCl6)Cl: influence of covalent and electrostatic factors on the supramolecular structure

A new inorganic supramolecular complex [Hg6As4](InCl6)Cl was synthesized. The complex crystallizes in the cubic space group Pa3 with the unit cell parameter a = 12.109(1) Å and Z = 4. The crystal structure of the complex is based on the ∞3[Hg6As4]4+ three-dimensional cationic host framework. The guest InCl63– and Cl– anions are located in the cavities of the framework. The host—guest interactions were examined by quantum-chemical calculations of the equilibrium geometry of the InCl63– anion and analysis of the periodic zero-potential surface of the supramolecular complex. It was demonstrated that the electrostatic factors dominate over the covalent factors in the organization of the supramolecular structure of [Hg6As4](InCl6)Cl.

57Fe and 119Sn probe Mössbauer spectroscopy investigation of perovskite-type double manganite family CaCuxMn7−xO12 (x = 0, 0.15, 3)

CaCuxMn7−xO12 (x = 0, 0.15, 3) manganites were studied by 57Fe and 119Sn probe Mössbauer spectroscopy. It was established that the 57Fe and 119Sn probe cations are stabilized in the octahedral positions of the manganite structures by substituting the manganese cations. The magnetic and structure phase transition temperatures of CaMn7O12 and CaCu0.15Mn6.85O12 manganites fell upon the introduction of 57Fe probe cations into their structures. It was concluded that intrasublattice Mn4+-O-Mn4+ exchange interactions play a noticeable role in the formation of the magnetic structure of CaCu3Mn4O12 manganite.

High oxygen pressures and the stabilization of the highest oxidation states of transition metals : Mössbauer spectroscopic characterization of the induced electronic phenomena

High oxygen pressures are a fruitful tool for the stabilization of the highest formal oxidation states of transition metals (Mn+) leading to the strongest chemical bonds; the improvement of the Mn+-O bond covalency induces different electronic phenomena. Among the physical characterizations applied to investigate such phenomena, 57Fe and 119Sn Mössbauer spectra are evaluated for studying unusual electronic configurations, orbital ordering, charge disproportionation and insulator-metal transitions in the perovskites series of 57Fe doped RENiO3 nickelates (RE = rare earths, Y and Tl) and 119Sn doped AEFeO3 ferrates (AE = Ca, Sr).

Crystal structure and thermal stability of Ni151.5Pb24S92. Search for selenium- and tellurium-containing analogs

The crystal structure of the subvalent nickel—lead sulfide, which has been described previously as Ni60Pb9S31, was established and the composition of this sulfide was refined based on powder X-ray diffraction data. The true Ni151.5Pb24S92 composition of this compound was confirmed by the EDX techniques. The temperature range of stability of this compound (490—578 °C) was refined by differential thermal analysis. In the search for analogs, the triangulation of the Ni—Pb—Se and Ni—Pb—Te systems at 540 °C was carried out for the first time. No new ternary phases were detected.