scholarly journals On the incorporation of strontium into the crystal structure of bredigite: structural effects and phase transition

2021 ◽  
Author(s):  
Volker Kahlenberg ◽  
Lukas Prosser ◽  
Michael F. Salzmann ◽  
Clivia Hejny
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Solid Solution ◽  
Single Crystal ◽  
Mode Analysis ◽  
Nominal Composition ◽  
Solid Solution Series ◽  
Space Group ◽  
Cell Parameters ◽  
Solution Series

AbstractSr-substitution in the crystal structure of bredigite has been studied in detail. Samples of a hypothetical solid-solution series with nominal composition Ca7-xSrxMg[SiO4]4 (x = 0, 2, …,7) have been prepared from sinter reactions in the temperature range between 1275 and 1325 °C and characterized using powder and single-crystal X-ray diffraction. Synthesis runs between x = 1 and x = 4 resulted in compounds with increasing Sr contents, for which single-crystal diffraction studies revealed the following Sr/(Sr + Ca) atomic ratios: 0.133,0.268, 0.409 and 0.559. They are isostructural to the pure calcium end-member (x = 0) and adopt the orthorhombic space group Pnnm. Evolution of the unit-cell parameters and cell volumes of the solid-solution series are defined by linear or nearly linear trends when plotted against the Sr/(Sr + Ca) atomic ratio. Replacement of calcium with strontium atoms on the different sites shows clear preferences for specific positions. For the experiment with x = 5, formation of bredigite-related single-crystals with Sr/(Sr + Ca) = 0.675 was observed. These samples, however, exhibited a halved c lattice parameter when compared with the corresponding value in the Pnnm structure, pointing to a compositionally induced phase transition somewhere in region between Sr/(Sr + Ca) = 0.559 and 0.675. The crystal structure of this new phase with composition Ca2.32Sr4.82Mg0.86[SiO4]4 was successfully determined in space group Pbam. Basic crystallographic data are as follows: a = 18.869(2) Å, b = 6.9445(8) Å, c = 5.5426(6) Å, V = 726.28(14) Å3, Z = 2. Structure determination was accomplished using charge flipping. Subsequent least-squares refinements resulted in a residual of R(|F|) = 2.70% for 822 independent reflections and 87 parameters. The Pbam- and the Pnnm-structures are in a group-subgroup relationship and topologically related. Both are based on so-called pinwheel-like MSi6O24 clusters consisting of a central magnesium-dominated [MO6]-octahedron as well as six attached [SiO4]-tetrahedra. The clusters are linked into chain-like elements running along [001]. Linkage between the chains is provided by mixed Sr/Ca positions with 6 to 10 oxygen ligands. Differences between the two phases result from changes in Sr-Ca site occupancies in combination with displacements of the atoms and tilts of the tetrahedra. The distortion pattern has been studied using group-theoretical methods including mode analysis. Notably, for the samples with x = 6 and x = 7—the latter corresponding to the hypothetical pure strontium end-member composition—no bredigite-type phases could be identified, indicating that there is an upper limit for the Sr-uptake.

Structural and Raman spectroscopic characterization of pyroxene-type compounds in the CaCu1−xZnxGe2O6solid-solution series

2017 ◽  
Vol 73 (3) ◽  
pp. 419-431 ◽  
Author(s):  
Günther J. Redhammer ◽  
Gerold Tippelt ◽  
Andreas Reyer ◽  
Reinhard Gratzl ◽  
Andreas Hiederer
Keyword(s):  
Solid Solution ◽  
Raman Spectroscopy ◽  
Phase Change ◽  
Single Crystal ◽  
Spectroscopic Characterization ◽  
Phase Changes ◽  
Solid Solution Series ◽  
Teller Distortion ◽  
Cell Parameters ◽  
Solution Series

Pyroxene-type germanate compounds with the composition CaCuGe2O6–CaZnGe2O6have been synthesizedviaa solid-state ceramic sintering route. Phase-pure polycrystalline and small single-crystal material was obtained all over the series, representing a complete solid-solution series. Differential thermal analysis, single-crystal X-ray diffraction and Raman spectroscopy were used to characterize phase stability, phase changes and structural alterations induced by the substitution of Cu2+with Zn2+. Whereas pure CaCuGe2O6exhibitsP21/csymmetry with a strong distortion of theM1 octahedra and two different Ge sites, one of them with an unusual fivefold coordination, the replacement of Cu2+by Zn2+induces a chemically driven phase change to theC2/csymmetry. The phase change takes place around Zn2+contents of 0.12 formula units and is associated with large changes in the unit-cell parameters. Here, the increase ofcby as much as 3.2% is remarkable and it is mainly controlled by an expansion of the tetrahedral chains. Further differences between theP21/candC2/cstructures are a more regular chain of edge-sharingM1 octahedra as a consequence of more and more reduced Jahn–Teller distortion and a less kinked, symmetry-equivalent tetrahedral chain. The coordination of the Ca site increases from sevenfold to eightfold with large changes in the Ca—O bond lengths during the phase change. Raman spectroscopy was mainly used to monitor theP21/ctoC2/cphase change as a function of composition, but also as a function of temperature and to follow changes in specific Raman modes throughout the solid-solution series.

On the symmetry and crystal structure of aguilarite, Ag4SeS

2013 ◽  
Vol 77 (1) ◽  
pp. 21-31 ◽  
Author(s):  
L. Bindi ◽  
N. E. Pingitore
Keyword(s):  
Crystal Structure ◽  
Solid Solution ◽  
Structural Study ◽  
Type Locality ◽  
Solid Solution Series ◽  
Chemical Formula ◽  
Space Group ◽  
Solution Series ◽  
System A ◽  
History Of

AbstractAn examination of a specimen of aguilarite from the type locality provides new data on the chemistry and structure of this mineral. The chemical formula of the crystal used for the structural study is (Ag3.98 Cu0.02)(Se0.98 S0.84 Te0.18), on the basis of 6 atoms. The mineral was found to be monoclinic, crystallizing in space group P 21/n, with a = 4.2478(2), b = 6.9432(3), c = 8.0042(5) Å , β = 100.103(2)º, V = 232.41(2) Å3 and Z = 4. The crystal structure [refined to R1 = 0.0139 for 958 reflections with I > 2 σ (I)] is topologically identical to that of acanthite, Ag2S. It can be described as a body-centred array of tetrahedrally coordinated X atoms (X = S, Se and Te) with Ag2X3 triangles in planes nearly parallel to (010); the sheets are linked by the Ag1 silver site, which has twofold coordination.Aguilarite is definitively proved to be isostructural with acanthite; it does not have a naumannite-like structure, as previously supposed. Our data support the hypothesis that there are two solid solution series in the system: a monoclinic 'acanthite-like' series (from Ag2S - Ag2S0.4Se0.6), and an orthorhombic 'naumannite-like' series (from Ag2S0.3Se0.7-Ag2Se). This is supported by data gathered on synthetic counterparts. Aguilarite remains as a valid as a mineral species, but it should be described as the Se-analogue of acanthite.In this study we also (1) review the history of the aguilarite; (2) compare properties of synthetic and natural aguilarite; and (3) demonstrate how earlier researchers erred in describing aguilarite as orthorhombic.The Te-bearing composition of the studied aguilarite crystal suggests the possibility of a solid solution with cervelleite (Ag4TeS).

Two lithium tricyanomethanide compounds: syntheses and single-crystal structure determination of LiK[C(CN)3]2 and Li[C(CN)3]·½ (H3C)2CO

2015 ◽  
Vol 70 (3) ◽  
pp. 191-196 ◽  
Author(s):  
Olaf Reckeweg ◽  
Francis J. DiSalvo
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Single Crystals ◽  
Structure Determination ◽  
Monoclinic Space Group ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Cell Parameters ◽  
New Compounds

AbstractThe new compounds LiK[C(CN)3]2 and Li[C(CN)3]·½ (H3C)2CO were synthesized and their crystal structures were determined. Li[C(CN)3]·½ (H3C)2CO crystallizes in the orthorhombic space group Ima2 (no. 46) with the cell parameters a=794.97(14), b=1165.1(2) and c=1485.4(3) pm, while LiK[C(CN)3]2 adopts the monoclinic space group P21/c (no. 14) with the cell parameters a=1265.7(2), b=1068.0(2) and c=778.36(12) pm and the angle β=95.775(7)°. Single crystals of K[C(CN)3] were also acquired, and the crystal structure was refined more precisely than before corroborating earlier results.

The Crystal Structure of Bi2PbMnO4(PO4)2, a Member of a New Solid Solution Series in the Bi–Pb–Mn–P Oxide System

2002 ◽  
Vol 165 (2) ◽  
pp. 324-333 ◽  
Author(s):  
Olivier Cousin ◽  
Marielle Huve ◽  
Pascal Roussel ◽  
Olivier Perez ◽  
Hugo Steinfink
Keyword(s):  
Crystal Structure ◽  
Solid Solution ◽  
Oxide System ◽  
Solid Solution Series ◽  
Solution Series

scholarly journals Struktur- und Phasenübergangsuntersuchungen an β-Li2ZnGe/ Structure and Phase Transition Investigations on β-Li2ZnGe

1981 ◽  
Vol 36 (8) ◽  
pp. 917-921 ◽  
Author(s):  
Hans-Otto Cullmann ◽  
Heinz-Walter Hinterkeuser ◽  
Hans-Uwe Schuster
Keyword(s):  
Phase Transition ◽  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Single Crystal ◽  
Ternary Compound ◽  
Type Structure ◽  
Crystal Data ◽  
Space Group ◽  
Cell Parameters ◽  
Structure Space

Abstract The ternary compound β-Li2ZnGe was prepared and its structure determined from powder and single crystal data. The compound crystallizes in a modified Na3As type structure, space group Ṗ̇̇̇̇̇̇̇̇̇̇̇̇̇̇3̄m 1 - D33d.The cell parameters are: a = 432.6 pm, c = 1647.0 pm, c/a= 3.83.A phase transition between a-and β-Li2ZnGe was found and the reaction of the elements lithium, zinc and germanium to a-Li2ZnGe was followed by differential thermal analysis. The temperatures and the enthalpies of transition and fusion were determined.

Crystal chemistry of lamprophyllite-group minerals from the Murun alkaline complex (Russia) and pegmatites of Rocky Boy and Gordon Butte (USA): single crystal X-ray diffraction and Raman spectroscopy study

2021 ◽  
Vol 77 (2) ◽  
Author(s):  
Sergey M. Aksenov ◽  
Anastasia D. Ryanskaya ◽  
Yuliya V. Shchapova ◽  
Nikita V. Chukanov ◽  
Nikolay V. Vladykin ◽  
...  
Keyword(s):  
Solid Solution ◽  
Single Crystal ◽  
Raman Spectra ◽  
Crystal Chemistry ◽  
Solid Solution Series ◽  
X Ray Diffraction ◽  
Alkaline Complex ◽  
Oh Groups ◽  
X Ray ◽  
Solution Series

Specific features of the crystal chemistry of lamprophyllite-group minerals (LGMs) are discussed using the available literature data and the results of the single-crystal X-ray diffraction and a Raman spectroscopic studies of several samples taken from the Murun alkaline complex (Russia), and Rocky Boy and Gordon Butte pegmatites (USA) presented here. The studied samples are unique in their chemical features and the distribution of cations over structural sites. In particular, the sample from the Gordon Butte pegmatite is a member of the barytolamprophyllite–emmerichite solid solution series, whereas the samples from the Murun alkaline complex and from the Rocky Boy pegmatite are intermediate members of the solid solution series formed by lamprophyllite and a hypothetical Sr analogue of emmerichite. The predominance of O2− over OH− and F− at the X site is a specific feature of sample Cha-192 from the Murun alkaline complex. New data on the Raman spectra of LGMs obtained in this work show that the wavenumbers of the O—H stretching vibrations depend on the occupancies of the M2 and M3 sites coordinating with (OH)− groups. Cations other than Na+ and Ti4+ (mainly, Mg and Fe3+) can play a significant role in the coordination of the X site occupied by (OH)−. Data on polarized Raman spectra of an oriented sample indicate that the OH groups having different local coordinations have similar orientations with respect to the crystal. The calculated measures of similarity (Δ) for lamprophyllite and ericssonite are identical (0.157 and 0.077 for the 2M- and 2O-polytypes, respectively), which indicates that these minerals are crystal-chemically isotypic and probably should be considered within the same mineral group by analogy to the other mineralogical groups which combine isotypic minerals.

Phase transitions in solid solution series bismutocolumbite – stibiocolumbite (Bi-Sb)(Nb0.79Ta0.21)O4

2002 ◽  
Vol 217 (10) ◽  
Author(s):  
S. S. Kazantsev ◽  
D. Yu. Pushcharovsky ◽  
B. Maximov ◽  
V. Molchanov ◽  
S. Werner ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Solid Solution ◽  
Phase Transitions ◽  
Solid Solution Series ◽  
Solution Series

AbstractThe crystal structure of bismutocolumbite, Bi(Nb

Spontaneous deformation of protocatechuic acid monohydrate crystals: crystallographic aspects

1983 ◽  
Vol 387 (1793) ◽  
pp. 311-330 ◽  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Hydrogen Bonding ◽  
Single Crystal ◽  
Protocatechuic Acid ◽  
Crystal Structure Analysis ◽  
Stable Phase ◽  
Space Group ◽  
Molecular Arrangement ◽  
Two Phases

Remarkable aspects of the crystallization of 3,4-dihydroxybenzoic acid (protocatechuic acid, PCA) from water as described by R. W. Wood ( Proc. R. Soc. Lond . A 197,283-294 (1949)) are confirmed. This compound crystallizes as the monohydrate in four different polymorphic phases: three are triclinic (oblique needles, needles and rhombs) and belong to one subgroup, while the fourth, monoclinic, phase constitutes a separate subgroup. It is probable that the triclinic rhombs are the stable phase at 25° C, with the other phases monotropically related to it. Crystal data for the triclinic needles are a = 9.926(9), b = 9.532(9), c = 8.131(8)Å, α = 100.8(1), β = 90.7(1), γ = 102.4(1)°, Z = 4, space group P1 - ; and for th e triclinic rhombs a = 12.693(9), b = 8.011(6), c = 8.121(6) Å, α = 72.2(1), β = 108.5(1), γ = 103.2(1)°, Z = 4, space group P1 - . Both crystals can be described in terms of a unit cell containing eight formula units, with dimensions a ≈ 12.7, b ≈ 9.5, c ≈ 13.0 Å, α ≈ 88, β ≈ 101, γ ≈ 107°; the space group for the triclinic needles is B1 - and for the triclinic rhombs A1 - . Crystal structure analyses (four-circle diffractometer, MoKα) of these two phases (triclinic needles, 1287 reflexions used in the final refinement cycle, R F = 11.1%; triclinic rhombs, 1761 reflexions, R F = 6.9%) show that both contain essentially similar layer pairs of PCA and H 2 O molecules, with hydrogen bonding both within each layer and, apparently, between them; however, the stacking of the layer pairs in the two phases differs. The crystals of the oblique needles are so small and unstable to stress that crystal structure analysis was not possible. The crystal structure of the monoclinic needles ( a = 12.32(1), b = 3.64(1), c = 17.60(2) Å, β = 107.7(2)°, Z = 4, space group P2 1 / n was determined (CuK α , 787 reflexions, R F = 6.8%); the overall molecular arrangement differs from that in the triclinic phases in an absence of PCA•H 2 O layers although there are distinct resemblances between the hydrogen bonding schemes. The phase transition ‘oblique needles → triclinic needles’ is ‘single crystal to single crystal’ and is a topotaxic transition. The phase transition ‘triclinic needles → triclinic rhombs’ is ‘single crystal to oriented polycrystal’ and is described as partially topotaxic, there being preservation of layer arrangement but not of complete three-dimensional orientation.

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