Crystal structure of zirconium-rich seidozerite

The crystal structure of seidozerite was refined (a Siemens P4 diffractometer, MoK _α radiation, 1180 independent reflections, anisotropic refinement, R = 0.053). The monoclinic unit-cell parameters are a = 5.627(1) Å, b = 7.134(1) Å, c = 18.590(4) Å, β = 102.68(1)°, sp. gr. P2/c, Z = 4. The structural formula, Na_1.6Ca_0.275Mn_0.425Ti_0.575Zr_0.925[Si₂O₇]OF, agrees well with the results of the electron probe analysis. Seidozerite is demonstrated to belong to the meroplesiotype polysomatic series including the structures of more than 30 titano-and zirconosilicates.     

Crystal structures of K-and Cs-exchanged forms of zorite

The crystal structures of K-and Cs-exchanged forms of zorite were studied by X-ray diffraction and IR spectroscopy: K_4.75Na_1.82[Ti(Ti_0.79Nb_0.20)₄Si₁₂O₃₄(O,OH)_5.2] × 10.62 H₂O (sp. gr. Cmmm, R= 0.0481 for 516 independent reflections) and Cs_4.34Na_1.90[Ti(Ti_0.80Nb_0.18)₄Si₁₂O₃₄(O,OH)₅] × 5.37 H₂O (sp. gr. Cmmm, R = 0.0285 for 621 independent reflections). Both structures retain the mixed polyhedral framework of zorite: Na₆Ti(Ti,Nb)₄(Si₆O₁₇)₂(O,OH)₅ × nH₂O, where n ～ 11. It is shown that the positions of the atoms located in the cavities of the frameworks of these compounds differ from those in the structures of zorite and its synthetic analogs.     

Crystal structure of byelorussite-(Ce) NaMnBa<Subscript>2</Subscript>Ce<Subscript>2</Subscript>(TiO)<Subscript>2</Subscript>[Si<Subscript>4</Subscript>O<Subscript>12</Subscript>]<Subscript>2</Subscript>(F,OH) · H<Subscript>2</Subscript>O

The crystal structure of the mineral byelorussite-(Ce) NaMnBa₂Ce₂Ti₂Si₈O₂₆(F,OH) · H₂O belonging to the joaquinite group was solved and refined to R = 0.033 based on 4813 reflections with I > σ2(I). The parameters of the orthorhombic unit cell are a = 22.301(4) Å, b = 10.514(2) Å, c = 9.669(2) Å, V = 2267.1(8) ų, sp. gr. Ama2, and Z = 4. The structure is composed of three-layer sheets, which consist of dimers of edge-sharing Ti octahedra located between isolated four-membered [Si₄O₂] rings. The sheets are linked to each other by Mn 5-vertex polyhedra to form a heteropolyhedral framework. Large cavities in the framework are occupied by Na 6-vertex polyhedra, Ba 11-vertex polyhedra, and REE 9-vertex polyhedra.     

Electron microscopic study of austenite microtwins and their influence on the crystallographic features of the pearlitic transformation

The crystallographic relationship between the structural components in high-carbon 120G4 steel after a partial isothermal pearlitic transformation has been studied by TEM. It has been found that a high density of microtwins and stacking faults was observed in the retained austenite. A new type of crystallographic relationship has been detected—parallelism of close-packed directions and planes of the structural components of fine-plate pearlite to one of the variants of twinned austenite.     

Crystal structure of loparite

The crystal structure of the cubic modification of the natural mineral loparite has been studied for the first time by the methods of the X-ray diffraction analysis (γMoK _α radiation, 105 independent reflections with I > 3σ(I), R = 0.041 in the anisotropic approximation). The structure belongs to the perovskite type (ABO ₃) with the double period of the cubic unit cell, a = 7.767(1) Å (sp. gr. Pn3m; Z = 2 for the composition (Ca,Na,Ce)(Na,Ce)₃(Ti,Nb)₂Ti₂O₁₂. Period doubling is explained by ordering of cations both in the A and the B positions.     

Crystal Chemistry of Cation-Exchanged Forms of Hilairite: New Experimental Data and Chemical Composition—Structure—Genesis Relations

Crystallography Reports - The crystal structures of cation-exchanged forms of hilairite obtained at 90°C (Pb- and Rb- exchanged samples (Pb0.60Na0.40H0.40ZrSi3O9 ? 3H2O [R32, a =...     

Corrector estimates in homogenization of a nonlinear transmission problem for diffusion equations in connected domains

This paper is devoted to the homogenization of a nonlinear transmission problem stated in a two-phase domain. We consider a system of linear diffusion equations defined in a periodic domain consisting of two disjoint phases that are both connected sets separated by a thin interface. Depending on the field variables, at the interface, nonlinear conditions are imposed to describe interface reactions. In the variational setting of the problem, we prove the homogenization theorem and a bidomain averaged model. The periodic unfolding technique is used to obtain the residual error estimate with a first-order corrector.     

Study of infrared spectrum of 3,3′-dichloroindanthrone

A complete calculation has been performed for the infrared spectrum of the molecule of 3,3-dichloroindanthrone, including vibration frequencies and intensities and the spectral curve. The satisfactory agreement that has been obtained between the calculated and experimental spectra has made it possible to interpret the spectrum in detail; to determine the characteristic spectral regions for manifestation of vibrations that pertain in form to such structural fragments of the molecule as the anthraquinone fragment, the nitrogen-containing ring, and the ring that embodies a hydrogen bond; and to obtain information on the sensitivity of vibrations to chlorination of indanthrone. The features that have been revealed have the character of a spectrum/structure correlation and can be used for analytical purposes.K. A. Timiryazev Agricultural Academy. Scientific-Research Institute of Physical Problems. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 190–196, January–February, 1993.     

New data on vlasovite: Refinement of the crystal structure and the radiation damage of the crystal during the x-ray diffraction experiment

The crystal structure of vlasovite obtained from the Kipawa alkaline complex in Quebec is refined to R _F = 0.053 for 1515 unique reflections with |F| > 4σ(F). The parameters of the monoclinic unit are as follows: a = 11.063(8) Å, b = 10.15(1) Å, c = 8.60(1) Å, β = 100.3(1)°, space group C2/c, and Z = 4. The X-ray diffraction, electron microprobe, and IR spectroscopic data indicate that, under X-ray radiation, the specimen suffers radiation damage, which is accompanied by a partial removal of Na atoms, incorporation of H₂O molecules into the structure, and, possibly, a change in the configuration of the (Si,O) framework.