Yu. V. Seryotkin

Synthesis and crystal structure of silver–gold sulfide AgAuS. Four-fold interpenetrated three-dimensional [(Au,Ag)10S8]-networks

Crystals of the silver(I) thioaurate(I), AgAuS, were obtained by fusing the elements in stoichiometric amounts. The X-ray diffraction analysis showed that the synthesized phase AgAuS represents a new structural type. The unit cell parameters are a = 13.4235(3), c = 9.0873(4) A, V = 1418.07(6) A3 and Z = 24, and the space group is Rm. The sublattice of sulfur atoms has a strongly distorted body-centered cubic packing. All Au atoms are in a typical linear coordination with sulfur ones. Three-quarters of the silver atoms are surrounded by distorted tetrahedra of sulfur atoms, while the rest of the silver atoms are involved in a linear motif typical of Au atoms as well. The resulting motif is composed of four-fold interpenetrating networks of linearly coordinated metals with 2- and 4-connected sulfur atoms: [Au8[2]Ag2[2]S6(2)S2(4)]. The formula of AgAuS can be represented as Ag24[4][Au8[2]Ag2[2]S8]4. The features of the AgAuS structure suggest the possibility of wide variation in the Auu2006:u2006Ag ratio.

Phase transition at thermal dehydration in stilbite

Thermal dehydration of stilbite was investigated by thermogravimetry and in situ X-ray powder diffraction. Sample mass changes continuously over the whole temperature range, with anomaly near 175xa0°C described in terms of the second-order phase transition with changes in symmetry from F-centered unit cell to A-centered one. This contradicts to the step-wise change in sample mass and the first-order phase transition with symmetry changing from F2/m to Amma reported in literature. The change in the order of the phase transition by means of the changes in experimental techniques is discussed.

Synthesis and crystal structure of gold–silver sulfoselenides: morphotropy in the Ag3Au(Se,S)2 series

Gold–silver sulfoselenides of Ag3Au(Se,S)2 series—Ag3AuSe1.5S0.5, Ag3AuSeS, and Ag3AuSe0.5S1.5—have been synthesized by fusing the elements in the required stoichiometric amounts in evacuated quartz ampoules. The single crystal X-ray diffraction data indicate the existence of two solid-solution series: petzite-type cubic Ag3AuSe2—Ag3AuSeS (space group I4132) and trigonal Ag3AuSe0.5S1.5—Ag3AuS2 (space group

The deformation mechanism of a pressure-induced phase transition in dehydrated analcime

Roverline{3} c

Probable metal–insulator transition in Ag4SSe

). Both crystal structures differ in the distribution of Ag+/Au+ cations in the same distorted body-centered cubic sublattice of chalcogen anions. The morphotropic transformation results from the shrinkage of anion packing accompanied by the shortening of Ag–Ag distances. The structure of uytenbogaardtite mineral, earlier incorrectly interpreted as a tetragonal or cubic cell, is similar to that of the trigonal Ag3AuS2 end-member.

The thermal behavior of secondary analcime as leucite derivate and its structural interpretation

Three natural minerals of ettringite group were investigated by TG to refine their chemical composition. Two samples are ettringite Ca5.97Mg0.01Sr0.02Al1.99Cr0.01(SO4)3(OH)12·23.7H2O and bentorite Ca5.99Mg0.01Cr1.95Al0.01Si0.03(SO4)2.82·(CO3)0.20(OH)12·19.4H2O, but the third one Ca5.99Na0.01Al1.38Si0.62(SO4)2.49·(CrO4)0.36·(CO3)0.46(OH)12·15.8H2O has found to be a solid solution among ettringite, thaumasite, and chromate-ettringite, not registered yet as a new mineral species. Similar phase is well known in concrete formed with Cr6+ admixture, but is found for the first time as a natural compound. X-ray single-crystal investigation allowed us to refine the structure and support substitution (SO4)2−xa0↔xa0(CrO4)2− in natural minerals of ettringite group.

Crystal growth, structure, magnetic properties and theoretical exchange interaction calculations of Cu2MnBO5

Abstract The elastic and structural behaviour of dehydrated analcime in compression in a non-penetrating medium up to 3 GPa was studied in a diamond anvil cell using in situ synchrotron powder diffraction. A first-order phase transition at 0.4-0.7 GPa is accompanied by a symmetry change from monoclinic (I2/a) to pseudo-rhombohedral (R3) due to trigonalization of the aluminosilicate framework. This is due to the migration of cations to new positions close to the 6-membered rings forming the channels. The reduction of the mean aperture of the structure-forming 6- and 8-membered rings, as a result of tetrahedral tilting, leads to a 7.5% reduction in volume at the phase transition. The bulk modulus values are 38(2) GPa for the low pressure (LP) phase [fitted with a Murnaghan equation of state, Kʹ = 4 (fixed)] and 11(4) GPa for the high pressure (HP) phase [fitted with a third-order Birch-Mumaghan equation of state, Kʹ = 9(1)]. The elastic behaviour of the LP phase is anisotropic, with compressibilities βa:βb:βc in the ratio 1:4:2; the most compressible direction b coinciding with the orientation of empty 8-membered rings. The compressibility of the HP phase is isotropic. Trigonalization appears to be the most effective (and probably unique) mechanism of radical volume contraction for the ANA structure type.

Syntheses, crystal structure and luminescence properties of the novel isostructural KSrR(BO3)2 with R = Y, Yb, Tb

Abstract Single crystals of Fe-substituted Cu2Mn1-xFexBO5 ludwigites have been synthesized using flux technique (xu202f=u202f0.2, 0.4, 0.5 – in the initial flux system). Structural properties of the synthesized compounds were studied by the single crystal and powder X-ray diffraction analysis. Obtained results were analyzed in the relationship with parent compound Cu2MnBO5. It was revealed that the type of monoclinic distortions of Fe-substituted ludwigites is different from the structure of Cu2MnBO5. The real cation composition and local structure of Cu2Mn1-xFexBO5 ludwigites were studied using XANES and EXAFS techniques, respectively. Analysis of field and thermal dependencies of magnetization showed a high dependence of the magnetic properties of these ludwigites on x with changing the type of magnetic ordering.