Structure of the new mineral paratsepinite-Na and its place in the labuntsovite group

X-ray diffraction study of high-strontium Ti-enadkevichite showed that it is a new mineral, which was given the name paratsepinite-Na, sp. gr. C2/m, a double value of the parameter c, and a different distribution of the non-framework cations in comparison with tsepinite-Na. In particular, strontium is located not only in the hexagonal window of the small channel, but also in three positions of the large channel. The characteristics of the mosaic blocks constituting the crystal are studied. It is assumed that polysynthetic twinning in these crystals and many other representatives of this family is associated with the phase transformation occurring in this hydrothermal mineral during its cooling after formation. The comparison of all the three structures of the vuoriyarvite subgroups of the labuntsovite group allows us to explain the disability of vuoriyarvite to absorb strontium from the aqueous solution by its smaller unit-cell volume and higher framework charge in comparison with those of tsepinites.     

Crystal structure of litvinskite: A new natural representative of the lovozerite group

A new representative of the lovozerite group—Na, Zr, Mn-silicate litvinskite (Na, H₂O, □) ₃(□, Na, Mn²⁺)Zr[Si₆O₁₂(OH)₃(OH, O)₃]—was discovered in ultraagpaitic pegmatites from the Lovozero massif. The crystal structure of the mineral was solved on an automated Syntex P $\bar 1$ diffractometer (MoK _α radiation, 1398 reflections, 2θ/θ scanning technique, anisotropic refinement to R _hkl = 0.065). The unit-cell parameters are a = 10.589(7) Å, b = 10.217(8) Å, c = 7.355(5) Å, β = 92.91(5)°, V = 794.6(9) ų, sp. gr. Cm, Z = 2, d _calcd = 2.63 g/cm³. The structure of the mineral consist of a three-dimensional framework of discrete six-membered rings of Si-tetrahedra linked to isolated Zr-octahedra. The framework cavities are occupied by Na cations. The litvinskite composition and the structure differ from all known natural and synthetic compounds of the lovozerite group, which supports the assumption about diversity of mineral types in this group.     

Crystal structure of a new representative of the cancrinite group with a 12-layer stacking sequence of tetrahedral rings

The crystal structure of a 12-layer tounkite-like mineral of the cancrinite group was determined for the first time by single-crystal X-ray diffraction analysis (the unit-cell parameters are a = 12.757 Å, c = 32.211 Å). The structure was refined in the space group P3 to R = 0.035 using 3834 reflections with | F| > 2σ(F). Si and Al atoms occupy tetrahedral framework positions in an ordered fashion. The average distances in the tetrahedra are 〈Si-O〉 = 1.611 Å and 〈Al-O〉 = 1.723 Å. The stacking sequence of the layers is described as CACACBCBCACB, where A, B, and C are six-membered rings arranged around the [2/3 1/3 z], [1/3 2/3 z], and [0 0 z] axes, respectively. In the structure of the mineral, the columns along the [0 0 z] axis are composed of cancrinite cages. The columns along the [2/3 1/3 z] and [1/3 2/3 z] axes contain alternating cancrinite, bystrite, and liottite cages.     

Crystal structure and microtwinning of a calcium-rich analogue of labuntsovite

The structure of a new representative of the labuntsovite family, which was found in the Khibiny alkaline massif (the Kola Peninsula), was established by the method of X-ray diffraction analysis. The unit-cell parameters are a = 14.365(7) Å, b = 13.887(7) Å, c = 7.814(2) Å, β = 117.36(5)°, sp. gr. Cm, R _aniso = 0.058, 1385 F > 4σ(F). The mineral differs from other members of the family by the absence of Na-atoms and the high Ca-content. The Ca-polyhedron is reduced to a seven-vertex polyhedron (the average Ca-O distance is 2.48 Å) compared to the eight-vertex Na-polyhedron (the average Na-O distance is 2.57 Å). The structure channels are orderly occupied, thus lowering the symmetry to Cm.     

Structural characteristics of peroxo complexes of group IV and V transition metals. Review

Structural characteristics of peroxo complexes of transition metals of Groups IV and V (Ti, V, Nb, and Ta) with the ratios M: O₂ = 1: 1, 1: 2, 1: 3, and 1: 4 and alkyl peroxo complexes of Ti, Hf, and V have been considered. The structural manifestation of the trans effect of η²-coordinated peroxo ligand in pseudooctahedral Ti, Nb, and V monoperoxo complexes is characterized. The structural manifestations of the trans effect of multiply bonded peroxo and oxo ligands in monooxomonoperoxo complexes of vanadium(V) are compared.     

Crystal structure of a new ten-layer feldspathoid of the cancrinite group

A new cancrinite-group mineral with composition (Na,Ca)₂₄K₁₀[(Si,Al)₆₀O₁₂₀](SO₄)_5.6Cl_1.5(CO₃)_0.4·11H₂O from the Sacrofano Caldera (Italy) was studied by X-ray diffraction. The unit-cell parameters are a = 12.847 Å, c = 26.461 Å, sp. gr. P3; the R factor is 5.7% based on 3111 reflections with F > 5σ(F). The mineral has a ten-layer stacking sequence of six-membered rings ACACBCBCBCAC…, whereas franzinite (Na,K)₃₀Ca₁₀[Si₃₀Al₃₀O₁₂₀](SO₄)₁₀·2H₂O having the same unit cell (sp. gr. P321) is characterized by a stacking sequence ABCABACABCAB. Both minerals contain three types of cages, including the cancrinite cage. The distinguishing feature of the analog of franzinite is that it contains the largest cages (liottite and giuseppettite) instead of the sodalite and bystrite (losod) cages found in the franzinite structure.     

Structural mineralogy of the eudialyte group: A review

New data on the chemical composition and structure of minerals of the eudialyte group are reviewed with respect to their classification; structural prerequisites of their properties; and structural changes occurring upon isomorphous substitutions, decationization, hydration, and solid-phase transformations of eudialyte due to the processes of potassium metasomatism. The problems associated with the separation of mineral species are considered within the structural-chemical approach. The nomenclature of mineral species, their typomorphism, and a number of other problems important for modern mineralogy are discussed.     

Crystal structure of ilyukhinite,a new mineral of the eudialyte group

The crystal structure of ilyukhinite, a new mineral of the eudialyte group, is studied by X-ray diffraction. The mineral found in pegmatite bodies of the Kukisvumchorr Mountain (Khibiny alkaline complex) is characterized by low sodium content, high degree of hydration, and predominance of manganese over iron. The trigonal cell has the following parameters: a = 14.1695(6) and c = 31.026(1) Å; space group R3m. The structure is refined to final R = 0.046 in the anisotropic approximation of atomic displacements using 1527F > 3σF. The idealized formula of ilyukhinite (Z = 3) is written as (H₃O,Na)₁₄Ca₆Mn₂Zr₃Si₂₆O₇₂(OH)₂ · 3H₂O. The new mineral differs from other representatives of the eudialyte group by the predominance of both oxonium in the N positions of extra-framework cations and manganese in the М2 position centering the tetragonal pyramid.     

Structural characteristics of the boron nitride sphalerite modification synthesized in a shock wave

Crystallography Reports - The real structure of ultradispersed powders of sphalerite boron nitride synthesized under shock compression has been studied by X-ray diffraction. The lattice microstrain...     

Ikranite: Composition and structure of a new mineral of the eudialyte group

The crystal structure of a new mineral, ikranite, of the eudialyte group discovered in the Lovozero massif (the Kola Peninsula) was established by X-ray diffraction analysis. The crystals belong to the trigonal system and have the unit-cell parameters a = 14.167(2) Å, c = 30.081(2) Å, V = 5228.5 Å 3, sp. gr. R3m. Ikranite is the first purely ring mineral of the eudialyte group (other minerals of this group contain ring platforms of either tetrahedral or mixed types). It is also the first representative of the eudialyte group where Fe³⁺ prevail over Fe²⁺ ions.     

Structural characteristics of some lanthanide violurate complexes

The magnetic moments and the electronic spectra of violurate complexes of Ce³⁺, Pr³⁺, Pr⁴⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Ho³⁺, Er³⁺, and Yb³⁺ have been investigated. The solid complexes are paramagnetic and have magnetic moment values near to the ground state values of the free ions. Few cases differ, since there exist possible electronic transitions (4f → 5d) in case of Ce³⁺ complexes and (f → f) for Ho³⁺ and Dy³⁺ complexes. The magnetic measurements in connection with the electronic spectra were used to decide the different electronic structural configuration of elements and hence the configuration of the coordination polyhedra around the central metal ions of the investigated complexes.     

Model of the crystal structure of biachellaite as a new 30-layer member of the cancrinite group

A crystal-structure model of biachellaite was determined. Biachellaite is a new mineral of the cancrinite group found in a volcanic ejectum from the Biachella Valley near Sacrofano Caldera (Italy). The unitcell parameters are a = 12.913(1) Å and c = 79.605(5) Å, sp. gr. P3. This mineral is characterized by a 30-layer packing of six-membered rings stacked in the following order: ABC ABC ACA CBA CBA CBC ACB ACB ACB ABC.... This new member of the cancrinite group has the largest number of layers and a maximum period of c ～ 80 Å. The structure contains four types of cavities, from the smallest cancrinite cavity to the largest liottite cavity.     

Structural characteristics of gas hydrates within the framework of generalized crystallography

It is shown that the symmetry of the {5, 3, 3} polytope (four-dimensional dodecahedron) embedded into E⁴ enables one to derive all the polyhedra—cavities that make up gas hydrates from the {5, 3} dodecahedron. Consideration is given to the allomorphic embedding of the {5, 3} subgraph into the incidence graph of the Desargues configuration 10₃, which determines the mechanism of incorporation of guest molecules into the polyhedra—cavities of gas hydrates and their escape from these polyhedra at the symmetry level. The relationships obtained may be considered as a basis for an a priori derivation of the determined (periodic and aperiodic) structures of gas hydrates.     

Optics and spectroscopy of a Pb3Ga2Ge4O14:Nd3+ crystal, a new representative of the langasite family

Absorption and luminescent properties of a Pb₃Ga₂Ge₄O₁₄:Nd³⁺ crystal have been studied. The refractive indices are measured in the range from 0.405 to 1.064 μm, and the molecular refraction is calculated.     

Structural characteristics and connection mechanism of gold-catalyzed bridging silicon nanowires

Lateral, single-crystalline silicon nanowires were synthesized using chemical vapor deposition catalyzed by gold nanoparticles deposited on one of the vertical {1 1 1} sidewalls of trenches etched in Si(0 1 1) substrates. Upon encountering the opposing sidewalls of the trenches, the lateral nanowires formed a mechanically strong connection. The bridging connection at the opposing sidewall was observed using high-resolution transmission electron microscopy (TEM) to be epitaxial and unstrained silicon-to-silicon. Using energy-dispersive X-ray spectroscopy in TEM, gold could not be detected at the interface region where the nanowires formed a connection with the opposing sidewall silicon deposit but was detected on the surface adjacent to the impingement region. We postulate that a silicon-to-silicon connection is formed as the gold–silicon liquid eutectic is forced out of the region between the growing nanowire and the opposing sidewall.     

Structural and electrical characteristics of InGaAsN layers grown by LPE

Crystallographic and transport properties of nominally undoped and Sn-doped InGaAsN layers grown by low-temperature LPE have been studied and related to the growth conditions.In the case of lattice matching, flat and uniform mirror-like layers of 8–10 μm in thickness are obtained. The compositions of the layers under study have been determined by combination of X-ray microanalysis and X-ray diffraction methods to be In_0.035Ga_0.065As_0.086N_0.014. The lattice mismatch between layer and substrate Δa_l/a_s calculated from X-ray diffraction curves is less than?7×10^?4 for all samples. The layers grown at lower epitaxy temperatures exhibit the highest crystalline quality, better lattice match and better homogeneity. This is in good agreement with the results of morphological study by atomic force microscopy which show root mean-square surface roughness of 0.18 nm for the best layers.CV and Hall measurements reveal that intentionally undoped InGaAsN layers are n-type with free carrier concentration about one order of magnitude higher in comparison to layers not containing nitrogen and high electron mobility values over 2000 cm²/Vs. A dramatic reduction in the free carrier concentration and slightly increase in mobility are observed for Sn-doped InGaAsN layers.     

Structural study on a new Cs2S2(SO4)3 crystal

A new type of dicesium disulfur trisulfate, Cs₂S₂(SO₄)₃, crystal has been crystallized. Differential scanning calorimetry (DSC) and X‐ray diffraction measurements have been performed on this compound. The crystal does not reveal any structural phase transition in the temperature range from 120 to 920 K. The compound belongs to a cubic system with space group P2₁3 at room temperature. It is found that both Cs and S atoms located on special positions are 93% occupied and 7% in exchange with each other. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural chemistry of peroxo compounds of group VI transition metals: I. Peroxo complexes of chromium (a review)

The specific features revealed in the structure of the d ³ Cr(III), d ² Cr(IV), d ¹Cr(V), and d ⁰ Cr(VI) peroxo complexes with the ratios M:O₂ = 1:1, 1:2, and 1:4 are considered. It is noted that, in eleven compounds of the general formula Cr(O₂)_nO_m A _p (n = 1, 2, 4; m = 0, 1; p = 0–4), the metal atoms can be in four oxidations states: +3 (d ³), +4 (d ⁴), +5 (d ¹), and +6 (d ⁰). This property distinguishes chromium peroxo compounds from molybdenum and tungsten dioxygen complexes, which, with one exception, are represented by the d ⁰ M(VI) compounds.