A. I. Kurbakov

Mesoscopic magnetic inhomogeneities in the low-temperature phase and structure of Sm1−xSrxMnO3 (x < 0.5) perovskite

Results are presented of studies of the 154Sm1−xSrxMnO3 system using neutron powder diffraction and small-angle polarized neutron scattering. An analysis of the neutron diffraction spectra showed that at T < 180 K these exhibit typical Jahn-Teller distortions of the manganese-oxygen octahedrons which persist under further cooling and on transition of the sample to a metallic magnetically ordered state. The magnetic contribution to the diffraction is satisfactorily described using the (Ax(Ay)Fz) model and is interpreted as the coexistence of ferromagnetic and antiferromagnetic phases. The exaggerated widths of the diffraction lines indicate an appreciable contribution from microdeformations evidently associated with the inhomogeneity of the system. Small-angle polarized neutron scattering showed that the Sm system for x = 0.4 and 0.25 is magnetically inhomogeneous in the low-temperature phase. Ferromagnetic correlations occur on scales of around 200 Å and having dimensions greater than 1000 Å which, combined with the temperature hysteresis of the magnetic small-angle scattering intensity observed for an x = 0.4 sample in the low-temperature phase, suggests that the transition is of a percolation nature.

Synthesis and crystal structure determination of 6-phenyl-5-phenylsulfonyl-1,2,3,4-tetrahydropyrimidine-2-thione from neutron powder diffraction data

Abstract The title compound was synthesized by reaction of N-(azidomethyl)thiourea or N-(tosylmethyl)thiourea with α-phenylsulfonylacetophenone in the presence of sodium hydride followed by p-toluenesulfonic acid treatment of the obtained N-[3-oxo-3-phenyl-2-(phenylsulfonyl)propyl]thiourea. The molecular and crystal structure of 6-phenyl-5-phenylsulfonyl-1,2,3,4-tetrahydropyrimidine-2-thione (C14H13N2S2O2; space group P21/a; Z=4; a=17.396(1) Å, b=5.887(1) Å, c=15.665(2) Å, β=104.89(1)o) have been determined and refined from neutron (the neutron diffraction was very effective for describing of this system due to using of partial hydrogen-deuterium substitution) powder diffraction data using grid search and a Rietveld procedures. The crystal structure is formed by centrosymmetric hydrogen-bonded dimers along a axis.

Atomic structure and transport and magnetic properties of the Sm1−xSrxMnO3 system

This is the first study of the temperature dependences of the atomic structure by neutron diffraction, as well as of the resistivity, differential magnetic susceptibility, and magnetoresistance of the ceramic system 154Sm1−xSrxMnO3 (x∼0.16–0.4). Samples (x⩾0.3) having an initially orthorhombic structure transfer upon cooling from the insulating to the metallic state and exhibit giant magnetoresistance, which at liquid-helium temperature reaches as high as 90% in magnetic fields up to 30 kOe. At lower doping levels (x⩽0.25), the compound has monoclinic structure. The resistivity of such compounds in zero magnetic field displays insulating behavior upon lowering the temperature to 77 K.

The possibility of catalyst preparation for oxidation of monoxide carbon (CO) by help of systems types CuCr2−xCoxO4+nCuO and TiO2+nCuO (neutron diffraction study, oxidation efficiency)

Abstract This report will try to present some confirmation of the direct relation between structural peculiarities and physical/chemical properties (oxidation efficiency) by the example of two model systems: CuCr2−xCoxO4+nCuO (carrier) and TiO2 (carrier)+nCuO. More correct crystal structure for Cu(Cr/Co)2O4+nCuO system is proposed.