Polymorphism and topological features of compounds with the general formula A1−x+Bx2+ {Mx2+M1−x3+ [BP2O8(OH)]} (where x = 0, 1): Synthesis and structure refinement of Rb{V[BP2O8(OH)]}, analysis of the ion-migration paths, and comparative crystal chemistry of vanadium borophosphates

2021 ◽  
pp. 122831
Author(s):  
Sergey M. Aksenov ◽  
Julia S. Mironova ◽  
Natalia A. Yamnova ◽  
Anatoly S. Volkov ◽  
Olga V. Dimitrova ◽  
...  
Keyword(s):  
General Formula ◽  
Crystal Chemistry ◽  
Structure Refinement ◽  
Ion Migration ◽  
Topological Features

X-ray Structure Refinement and Vibrational Spectroscopy of Ca8Gd2 (PO4)6 O2

2013 ◽  
Vol 12 (10) ◽  
pp. 719-726
Author(s):  
R. Ayadi ◽  
Mohamed Boujelbene ◽  
T. Mhiri
Keyword(s):  
Solid State ◽  
General Formula ◽  
Vibrational Spectroscopy ◽  
Powder Diffraction ◽  
Infrared Spectra ◽  
Solid State Reaction ◽  
Structure Refinement ◽  
Unit Cell ◽  
Cell Group ◽  
X Ray

The present paper is interested in the study of compounds from the apatite family with the general formula Ca10 (PO4)6A2. It particularly brings to light the exploitation of the distinctive stereochemistries of two Ca positions in apatite. In fact, Gd-Bearing oxyapatiteCa8 Gd2 (PO4)6O2 has been synthesized by solid state reaction and characterized by X-ray powder diffraction. The site occupancies of substituents is0.3333 in Gd and 0.3333 for Ca in the Ca(1) position and 0. 5 for Gd in the Ca (2) position.  Besides, the observed frequencies in the Raman and infrared spectra were explained and discussed on the basis of unit-cell group analyses.

The crystal chemistry of rhodizite: a re-examination

1986 ◽  
Vol 50 (355) ◽  
pp. 163-172 ◽  
Author(s):  
A. Pring ◽  
V. K. Din ◽  
D. A. Jefferson ◽  
J. M. Thomas
Keyword(s):  
Single Crystal ◽  
Crystal Chemistry ◽  
Structure Refinement ◽  
High Resolution Electron Microscopy ◽  
Basic Structure ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Alkali Cations ◽  
X Ray ◽  
Using Data

AbstractThe crystal chemistry of rhodizite was re-examined using data from high-resolution electron microscopy (HREM), magic angle spinning nuclear magnetic resonance (MASNMR), a single crystal X-ray structure refinement, and a new chemical analysis. The analysis calculates to the formula: (K0.46Cs0.36Rb0.06 Na0.02)Σ0.90Al3.99Be4(B11·35Be0.55Li0.02)O28· The distribution of alkali cations was shown to be truly random by HREM images and computer image simulations. The distribution of boron and beryllium was monitored by MASNMR, the spectra for both elements gave only single resonances indicating that all beryllium and boron atoms are located in chemically equivalent sites. The structure of rhodizite was refined by single crystal X-ray diffraction techniques. The mineral is cubic a = 7.318(1) Å, space group P3. A full matrix least-squares refinement using 152 unique observed reflections [F > 3σ(F)] converged to R = 0.0344. The refinement confirmed the basic structure as determined by Taxer and Buerger (1967), 4 beryllium atoms of the unit cell were found to occupy a 4e special position, the remaining 0.5 being randomly distributed with the 11.35 boron atoms over the 12h sites.

The crystal structure of cesanite, Ca1+xNa4−x(SO4)3(OH)x · (1 − x)H2O, a sulphate isotypic to apatite

1983 ◽  
Vol 47 (342) ◽  
pp. 59-63 ◽  
Author(s):  
V. Tazzoli
Keyword(s):  
Crystal Structure ◽  
General Formula ◽  
Structure Refinement ◽  
Structural Features ◽  
Partial Substitution ◽  
Crystal Structure Refinement ◽  
Charge Balance ◽  
Space Group ◽  
The Relationship

AbstractCesanite, Ca1+xNa4−x(SO4)3(OH)x · (1 − x) H2O, is hexagonal, space group P63/m, a = 9.446(1) and c = 6.895(1) Å, Z = 2. The crystal structure refinement, carried out by utilizing 457 independent reflections (final R = 0.021), shows that cesanite is isotypic to hydroxyapatite. The P atom of apatite is completely replaced in cesanite by an S atom; the two independent Ca sites of apatite are occupied respectively by Na and Na + Ca, the charge balance being by partial substitution of H2O for OH− although the occupancy of the (H2O,OH−) sites is not complete. The relationship between the water vacancies and the structural features of the (Ca,Na) polyhedron is discussed. A new general formula for the apatite-wilkeite-ellestadite series is proposed.

Crystal chemistry of danalite from Daba Shabeli Complex (N Somalia)

1996 ◽  
Vol 60 (399) ◽  
pp. 375-379 ◽  
Author(s):  
P. Nimis ◽  
G. Molin ◽  
D. Visonà
Keyword(s):  
General Formula ◽  
Crystal Chemistry ◽  
The Other ◽  
The World ◽  
Alkali Granites ◽  
End Members ◽  
Host Rocks

Danalite is the Fe2+ end-member of the minerals of the helvite group, which have the general formula M8(BeSiO4)6S2, with M = (Mn,Fe2+,Zn). These minerals are relatively uncommon, although limited amounts are known at many localities round the world (e.g. Ragu, 1994; Larsen, 1988; Kwak and Jackson, 1986, and references therein). Their typical host rocks are skams, but occurrences in mineralized veins pegmatites, and altered alkali granites have also been reported. Danalite is rarer than helvite (Mn endmember) and genthelvite (Zn end-member) and, unlike the other two end-members, has never been found nor synthesized as a pure mineral (Mel'nikov et al., 1968).

Zaoyang chondrite cooling history from Fe2+-Mg intracrystalline ordering in pyroxenes

1994 ◽  
Vol 58 (390) ◽  
pp. 143-150 ◽  
Author(s):  
Gian Mario Molin ◽  
Mario Tribaudino ◽  
Elisabetta Brizi
Keyword(s):  
Cooling Rate ◽  
Exchange Reaction ◽  
Crystal Chemistry ◽  
Microprobe Analysis ◽  
Structure Refinement ◽  
Cooling History ◽  
Cooling Rates ◽  
X Ray ◽  
Fast Cooling ◽  
Polyhedral Volumes

AbstractThe crystal chemistry of clinopyroxene, orthopyroxene and olivine from a crushed fragment of the H5 Zaoyang chondrite has been investigated by X-ray structure refinement and detailed microprobe analysis. The meteoritic pyroxenes have cell and polyhedral volumes which compare well with such data from terrestrial pyroxenes that typically crystallize at low-pressure. Fe2+ and Mg are rather disordered in M1 and M2 sites of clino- and orthopyroxenes; the closure temperatures of the exchange reaction are 600 and 512°C respectively, which is consistent with a reasonably fast cooling rate, estimated to be of the order of 1°C/day.The closure temperature for the intercrystalline Ca-Mg exchange reaction for clino- and orthopyroxenes is 900°C as calculated from clino- and orthopyroxene intergrowth.The cooling rates obtained from Fe2+-Mg intracrystalline partitioning suggest a cooling of the order of degrees per day at temperatures of 600–500°C due to a strong loss of heat by irradiation.

scholarly journals Five-dimensional structure refinement of natural melilite, (Ca1.89Sr0.01Na0.08K0.02)(Mg0.92Al0.08)(Si1.98Al0.02)O7

2001 ◽  
Vol 57 (6) ◽  
pp. 739-746 ◽  
Author(s):  
Luca Bindi ◽  
Paola Bonazzi ◽  
Michal Dušek ◽  
Václav Petříček ◽  
Gervais Chapuis
Keyword(s):  
Data Collection ◽  
General Formula ◽  
Structure Refinement ◽  
Thermal Parameters ◽  
Dimensional Structure ◽  
Interatomic Distances ◽  
Final Model ◽  
Cell Parameters ◽  
Incommensurate Structure ◽  
Special Modification

The structure of a crystal of natural melilite from San Venanzo, Umbria (Italy) of the general formula X 2 T1(T2)2O7, where X = Ca0.945Sr0.005Na0.04K0.01, T1 = Mg0.92Al0.08 and T2 = Si0.99Al0.01, has been solved and refined as an incommensurate structure in five-dimensional superspace. The structure is tetragonal, superspace group P\bar 421 m:p4mg, cell parameters a = 7.860 (1), c = 5.024 (1) Å, modulation vectors q 1 = 0.2815 (3)(a* + b*), q 2 = 0.2815 (3)(−a* + b*). The data collection was performed on a KumaCCD diffractometer. The structure was refined from 7606 reflections to final R = 0.0481. A special modification of the refinement program Jana2000 was necessary to take into account overlapping of satellite reflections m × n = ±1, which could not be properly separated in the integration procedure. The final model includes modulations of the atomic positions as well as modulations of the thermal parameters. The latter are induced by strong differences in the neighbourhood of the actual modulated positions. The occupational modulation was neither significant for X nor for T1 sites and the sites were supposed to be occupied only by Ca and Mg, respectively. As a consequence of the Ca and O positional modulations six-, seven- and eightfold Ca coordination occur throughout the structure and the thermal ellipsoid changes its shape correspondingly. The positional modulation of the atoms causes variations in the interatomic distances which, however, do not affect bond-valence sums considerably, but induce flattening and rotation in T1 and T2 tetrahedra, respectively.

scholarly journals Crystal structure refinement and crystal chemistry of parasymplesite and vivianite

2021 ◽  
Vol 116 (4) ◽  
pp. 183-192
Author(s):  
Hidetomo HONGU ◽  
Akira YOSHIASA ◽  
Ginga KITAHARA ◽  
Yumiko MIYANO ◽  
Karin HAN ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Crystal Chemistry ◽  
Structure Refinement ◽  
Crystal Structure Refinement
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