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M1 Site (m1 + site)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Determination of the metal ordering in meteoritic (Fe,Ni)3P crystals

JOURNAL OF SYNCHROTRON RADIATION, Issue 2 2005
O. Moretzki
Synchrotron radiation diffraction studies of meteoritic (Fe,Ni)3P crystals have been performed to reveal the ordering of the elements Fe and Ni on the three metal sites M1, M2 and M3 of the unit cell. The , synthesis technique, which is a two-wavelength method using anomalous dispersion effects, was applied. For (Fe,Ni) phosphide crystals with different Fe:Ni ratios extracted from different meteorites, it was found that Ni occupies the M3 site and also partially the M2 site, avoiding the M1 position, whereas the M1 site is preferentially occupied by Fe. In connection with earlier results known from the literature, this metal distribution seems to be characteristic of this compound, and is independent of thermodynamic formation conditions. [source]

On the crystal chemistry of olivine-type germanate compounds, Ca1,+,xM1,,,xGeO4 (M2+ = Ca, Mg, Co, Mn)

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2008
Günther J. Redhammer
Germanate compounds, CaMGeO4 with M2+ = Ca, Mg, Co and Mn, were synthesized as single crystals by slow cooling from the melt or by flux growth techniques. All the compositions investigated exhibit Pnma symmetry at 298,K and adopt the olivine structure. The M2 site is exclusively occupied by Ca2+, while on M1 both Ca2+ and M2+ cations are found. The amount of Ca2+ on M1 increases with the size of the M1 cation, with the smallest amount in the Mg compound (0.1,atoms per formula unit) and the largest in the Mn compound (0.20,atoms per formula unit), while in Ca2GeO4, also with olivine structure, both sites are completely filled with Ca2+. When compared with those of Ca silicate olivine, the lattice parameters a and c are distinctly larger in the analogous germanate compounds, while b has essentially the same values, regardless of the tetrahedral cation, meaning that b is independent of the tetrahedral cation. Structural variations on the octahedrally coordinated M1 site are largely determined by the size of the M1 cation, the average M1,O bond lengths being identical in Ca silicate and Ca germanate olivine. Increasing the size of the M1 cation induces an increasing polyhedral distortion, expressed by the parameters bond-length distortion, octahedral angle variance and octahedral quadratic elongation. However, the Ca germanate olivine compounds generally have more regular octahedra than the analogous silicates. The octahedrally coordinated M2 site does not exhibit large variations in structural parameters as a consequence of the constant chemical composition; the same is valid for the tetrahedral site. [source]

Natural monoclinic AgPb(Bi2Sb)3S6, an Sb-rich gustavite

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009
Richard Pa
The crystal structure of the Sb-rich variety of the mineral gustavite, silver lead tris(dibismuth/antimony) hexasulfide, AgPb(Bi2Sb)3S6, consists of blocks of diagonal chains of four octahedra, viz. M1a (Bi), M2a (Sb/Bi), M2b (Bi/Sb) and M1b (Ag), separated by Pb atoms in a trigonal prismatic coordination. Two marginal octahedral sites, M1a and M1b, where the gustavite substitution Ag+ + Bi3+ = 2Pb2+ takes place, are formed by Bi and Ag, respectively. Two central octahedra, M2a and M2b, where the Bi3+ = Sb3+ substitution takes place, are formed by two mixed Bi/Sb sites with different occupancies of Bi and Sb. The alternating occupation of the M1 site by Bi and Ag atoms (which thus creates two distinct sites M1a and M1b) results in the monoclinic space group P21/c. A statistical distribution of Ag/Bi in the M1 position (one mixed Ag/Bi site) was reported for synthetic gustavite, resulting in the orthorhombic space group Cmcm. [source]

Chromium-based clinopyroxene-type germanates NaCrGe2O6 and LiCrGe2O6 at 298,K

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2008
Günther J. Redhammer
The structure analyses of sodium chromium digermanate, NaCrGe2O6, (I), and lithium chromium digermanate, LiCrGe2O6, (II), provide important structural information for the clinopyroxene family, and form part of our ongoing studies on the phase transitions and magnetic properties of clinopyroxenes. (I) shows C2/c symmetry at 298,K, contains one Na, one Cr (both site symmetry 2 on special position 4e), one Ge and three O-atom positions (on general positions 8f) and displays the well known clinopyroxene topology. The basic units of the structure of (I) are infinite zigzag chains of edge-sharing Cr3+O6 octahedra (M1 site), infinite chains of corner-sharing GeO4 tetrahedra, connected to the M1 chains by common corners, and Na sites occupying interstitial space. (II) was found to have P21/c symmetry at 298,K. The structure contains one Na, one Cr, two distinct Ge and six O-atom positions, all on general positions 4e. The general topology of the structure of (II) is similar to that of (I); however, the loss of the twofold symmetry makes it possible for two distinct tetrahedral chains, having different conformation states, to exist. While sodium is (6+2)-fold coordinated, lithium displays a pure sixfold coordination. Structural details are given and chemical comparison is made between silicate and germanate chromium-based clinopyroxenes. [source]