scholarly journals Modulated Structures, Microstructures and Subsolidus Phase Relations of Labradorite Feldspars

2021 ◽  
Vol 6 (1) ◽  
pp. 1
Author(s):  
Huifang Xu ◽  
Shiyun Jin ◽  
Seungyeol Lee
Keyword(s):  
Cooling Rate ◽  
Group Symmetry ◽  
Subsolidus Phase ◽  
Plagioclase Feldspar ◽  
Modulated Structure ◽  
Modulated Structures ◽  
Coupled Substitution ◽  
Density Modulation ◽  
Q Vector ◽  
Rich Side

The coupled substitution between Na+Si and Ca+Al, in the plagioclase solid solution, results in a continuous variation in the Al/Si ratio of the composition, which is the reason for the complicated ordering patterns in the intermediate plagioclase feldspars such as labradorite. Both fast-cooled and slow-cooled labradorite feldspars display the incommensurately modulated structures. The ordering pattern in the incommensurately modulated structures of e-plagioclase (characterized by the satellite diffraction peak called e-reflections) is the most complicated and intriguing. The modulated structure has a super-space group symmetry of X(αβγ)0, with a special centering condition of (½ ½ ½ 0), (0 0 ½ ½), (½ ½ 0 ½), and the q-vector has components (i.e., δh, δk, δl) along all three axes in reciprocal space. Displacive modulation, occupational modulation, and density modulation are observed in slowly cooled labradorite feldspars. No density modulation was observed in fast cooled (volcanic) labradorite feldspars. The amplitudes of the modulation waves are new parameters for quantifying the ordering state of labradorite. Iridescent labradorite feldspars display exsolution lamellae with an average periodicity ranging from ~150 nm to ~350 nm. Compositional difference between the lamellae is about 12 mole % in anorthite components. Areas or zones with red (or yellow) iridescent color (i.e., long lamellae periodicity) always contain more Ca (~1 to 3 mole %) than the areas with blue (or green) iridescent color within the same labradorite crystal. We proposed that the solvus for Bøggild intergrowth has a loop-like shape, ranging from ~An44 to ~An63. The Ca-rich side / zone has higher exsolution temperature than the Na-rich side / zone. The shapes of satellite peaks, the distances between e-reflections (modulation periods), and even the intensity of e-reflections may also be used to evaluate the ordering state or cooling rate of the plagioclase feldspar. Both modulated structure and the exsolution lamellae can be used as proxies for quantifying cooling rate of a labradorite and it’s host rock.

Incommensurately modulated structures and subsolidus phase relations of intermediate plagioclase feldspars

2020 ◽  
Author(s):  
Huifang Xu ◽  
Shiyun Jin
Keyword(s):  
Cooling Rate ◽  
Group Symmetry ◽  
Contrast Imaging ◽  
Subsolidus Phase ◽  
Plagioclase Feldspar ◽  
Modulated Structure ◽  
Modulated Structures ◽  
Density Modulation ◽  
Z Contrast ◽  
Rich Side

<p>Plagioclase feldspars are the most abundant mineral in the Earth’s crust. Intermediate plagioclase feldspars commonly display incommensurately modulated structure or aperiodic structure. Both fast-cooled and slow-cooled plagioclase feldspars display the incommensurately modulated structures. The ordering pattern in the incommensurately modulated structures of e-plagioclase (characterized by the satellite diffraction peak called e-reflections) are the most complicated and intriguing. The modulated structure has a superspace group symmetry of <em>X</em>-1(αβγ)0 with a special centering condition of (½ ½ ½ 0), (0 0 ½ ½), (½ ½ 0 ½), and the <em><strong>q</strong></em>-vector has components (i.e., δh, δk, δl) along all three axes in reciprocal space. Displacive modulation, occupational modulation, and density modulation are observed in slowly cooled labradorite feldspars. Z-contrast images show both Ca-Na ordering and density modulation. Local structure of lamellae domains has<em> I</em>1 symmetry. The neighboring lamellae domains are in inversion twinning relationship.  The results from Z-contrast imaging and low-temperature single XRD provide consistent structure with density modulation.  The amplitudes of the modulation waves are new parameters for quantifying the ordering state of plagioclase feldspars. Iridescent labradorite feldspars display exsolution lamellae with average periodicity ranging from ~ 150 nm to ~350 nm. Compositional difference between the lamellae is about 10 to 15 mole % in anorthite component. Areas or zones with red iridescent color (i.e., long lamellae periodicity) always contain more Ca (~ 1 to 3 mole %) than the areas with blue (or green) iridescent color within the same labradorite crystal.  We proposed that the solvus for Bøggild intergrowth has a loop-like shape ranging from ~An<sub>44</sub> to ~ An<sub>63</sub>. The Ca-rich side has higher temperature than the Na-rich side. The shapes of satellite peaks, the distances between e-reflections (modulation periods), and even the intensity of c-reflections may also be used evaluate the ordering state or cooling rate of the plagioclase feldspar. Both modulated structure and the exsolution lamellae can be used as proxies for quantifying cooling rate of a labradorite and its host rock.</p>

Structure of KNbOB2O5 – a commensurately modulated structure

2005 ◽  
Vol 61 (4) ◽  
pp. 361-366 ◽  
Author(s):  
Siegbert Schmid ◽  
Trixie Wagner
Keyword(s):  
Single Crystal ◽  
Diffraction Data ◽  
Group Symmetry ◽  
X Ray Diffraction ◽  
Modulated Structure ◽  
Space Group ◽  
X Ray ◽  
Average Structure ◽  
Modulated Structures ◽  
First Time

Members of the AMOB2O5 (A = K, Rb, Cs, Tl; M = Nb, Ta) family of compounds can be described as modulated structures with a single superspace group and very similar modulation functions. Single-crystal X-ray diffraction data (Mo Kα radiation) are used to solve and refine the structure of KNbOB2O5 in these terms for the first time. The average structure is solved and refined in the space group Pmn21. Subsequently, the atomic modulation functions are determined using JANA2000 and superspace-group symmetry Pmn21(0,0.375,0)s. The commensurately modulated structure is finally refined as a superstructure in the space group Pbn21 using SHELXS97 converging to R 1 = 0.024.

scholarly journals Processing Twinned-Modulated and Composite Structures from CCD / CMOS Images

2014 ◽  
Vol 70 (a1) ◽  
pp. C173-C173
Author(s):  
Charles Campana ◽  
Joerg Kaercher ◽  
John Chambers ◽  
Vaclav Petricek
Keyword(s):  
Composite Structures ◽  
Reciprocal Lattice ◽  
Image Data ◽  
Software Suite ◽  
Modulated Structure ◽  
Simultaneous Integration ◽  
Modulated Structures ◽  
Higher Dimensional ◽  
Multiple Domains ◽  
Q Vector

The Bruker APEX2 [1] software suite includes a full set of crystallographic programs for the solution and refinement of routine crystal structures. In addition to the standard tools required for routine problems, a number of advanced tools are also provided for analysis of non-merohedral twins and modulated structures. These tools include the CELL_NOW [2], SADABS [2] and TWINABS [2] programs and a Reciprocal Lattice Viewer with a q-vector analysis option. The Bruker SAINT [2] program is routinely used for the integration of image data collected with Bruker CCD (APEX II) or CMOS (PHOTON 100) two-dimensional detectors as part of the APEX2 software suite. SAINT has many advanced features for the processing of non-routine datasets. For example, a variety of new options have been implemented to facilitate the simultaneous integration of multiple domains for twinned and composite structures. Higher dimensional crystallography may be used to integrate modulated structures with up to three q-vectors. The output data for modulated structures may be output in either HKL5 or HKLF6 format suitable for input into the JANA2006[3] program. We will present results for one twinned-modulated structure and one composite structure to illustrate the use of the respective advanced options in SAINT to integrate images and JANA2006 to refine the structures.

Intergrowth of modulated structures in high Tc Bi-Sr-Ca-Cu-O superconductors

1990 ◽  
Vol 48 (4) ◽  
pp. 76-77
Author(s):  
A.Q. He ◽  
G.W. Qiao ◽  
J. Zhu ◽  
H.Q. Ye
Keyword(s):  
Twin Structure ◽  
Modulated Structure ◽  
High Tc ◽  
One Dimensional ◽  
Lattice Constants ◽  
Superconducting Phases ◽  
Modulated Structures ◽  
Layer Structures

Since the first discovery of high Tc Bi-Sr-Ca-Cu-O superconductor by Maeda et al, many EM works have been done on it. The results show that the superconducting phases have a type of ordered layer structures similar to that in Y-Ba-Cu-O system formulated in Bi2Sr2Can−1CunO2n+4 (n=1,2,3) (simply called 22(n-1) phase) with lattice constants of a=0.358, b=0.382nm but the length of c being different according to the different value of n in the formulate. Unlike the twin structure observed in the Y-Ba-Cu-O system, there is an incommensurate modulated structure in the superconducting phases of Bi system superconductors. Modulated wavelengths of both 1.3 and 2.7 nm have been observed in the 2212 phase. This communication mainly presents the intergrowth of these two kinds of one-dimensional modulated structures in 2212 phase.

scholarly journals Revisiting the Bøggild Intergrowth in Iridescent Labradorite Feldspars: Ordering, Kinetics, and Phase Equilibria

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 727
Author(s):  
Shiyun Jin ◽  
Huifang Xu ◽  
Seungyeol Lee
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Atom Probe ◽  
Phase Region ◽  
Two Phase ◽  
Subsolidus Phase ◽  
Plagioclase Feldspar ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission

The enigmatic Bøggild intergrowth in iridescent labradorite crystals was revisited in light of recent work on the incommensurately modulated structures in the intermediated plagioclase. Five igneous samples and one metamorphic labradorite sample with various compositions and lamellar thicknesses were studied in this paper. The lamellar textures were characterized with conventional transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The compositions of individual lamellae were analyzed with high-resolution energy-dispersive X-ray spectroscopy (EDS) mapping and atom probe tomography (APT). The average structure states of the studied samples were also compared with single-crystal X-ray diffraction data (SC-XRD). The Na-rich lamellae have a composition of An44–48, and the Ca-rich lamellae range from An56 to An63. Significant differences between the lamellar compositions of different samples were observed. The compositions of the Bøggild intergrowth do not only depend on the bulk compositions, but also on the thermal history of the host rock. The implications on the subsolidus phase relationships of the plagioclase feldspar solid solution are discussed. The results cannot be explained by a regular symmetrical solvus such as the Bøggild gap, but they support an inclined two-phase region that closes at low temperature.

The role of hydrogen bonds in order-disorder transition of a new incommensurate low temperature phase β-[Zn-(C7H4NO4)2]·3H2O

2018 ◽  
Vol 233 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Masoumeh Tabatabaee ◽  
Morgane Poupon ◽  
Václav Eigner ◽  
Přemysl Vaněk ◽  
Michal Dušek
Keyword(s):  
Low Temperature ◽  
Hydrogen Bonds ◽  
Dicarboxylic Acid ◽  
Room Temperature ◽  
Temperature Phase ◽  
Temperature Structure ◽  
Modulated Structure ◽  
Q Vector ◽  
Low Temperature Phase

AbstractThe room temperature structure withP21/csymmetry of the zinc(II) complex of pyridine-2,6-dicarboxylic acid was published by Okabe and Oya (N. Okabe, N. Oya, Copper(II) and zinc(II) complexes of pyridine-2,6-dicarboxylic acid.Acta Crystallogr. C.2000,56, 305). Here we report crystal structure of the low temperature phaseβ-[Zn(pydcH)2]·3H2O, pydc=C7H3NO4, resulting from the phase transition around 200K. The diffraction pattern of the low temperature phase revealed satellite reflections, which could be indexed with q-vector 0.4051(10)b* corresponding to (3+1)Dincommensurately modulated structure. The modulated structure was solved in the superspace groupX21/c(0b0)s0, whereXstands for a non-standard centring vector (½, 0, 0, ½), and compared with the room temperature phase. It is shown that hydrogen bonds are the main driving force of modulation.

X-ray structure refinement of (3 + 1)-dimensional incommensurate composite (1-x)Ta2O5.xWO3, x = 0.1

1996 ◽  
Vol 52 (2) ◽  
pp. 223-231 ◽  
Author(s):  
S. Schmid ◽  
K. Fütterer ◽  
J. G. Thompson
Keyword(s):  
Solid Solution ◽  
Composite Structure ◽  
Structure Refinement ◽  
Mean Square Displacement ◽  
Thermal Parameter ◽  
Group Symmetry ◽  
X Ray ◽  
Modulated Structures ◽  
Bond Valence Sum ◽  
Remarkable Agreement

The structure refinement of tantalum tungstate, (1−x) Ta2O5.xWO3, x = 0.1, as a (3 + 1)-dimensional incommensurately modulated composite structure was carried out using X-ray single-crystal diffraction data measured with Mo Kα radiation. The composite structure consists of two component substructures referred to as the metal-substructure (M), aM = 6.188 (1), bM = 3.665 (1), cM = 3.886 (1) Å, and the oxygen-substructure (O), aO = aM , bO = 2.251 Å = bM /1.628, cO = cM , respectively. The primary modulation wavevector of the M substructure is chosen to be q M = b O * = 1.628 b M * . The overall superspace-group symmetry is C′mmm(0β0)s00. The structure was refined to an overall wR = 0.0561. The structures of the compounds x = 0.267 (Ta22W4O67) and x = 0.14 (Ta74W6O203), also members of the (1 − x) Ta2O5.xWO3, 0 ≤ x ≤ 0.267, solid solution, were rerefined as incommensurately modulated structures using intensity data reported previously. The displacive modulation wave amplitudes obtained from these refinements are in remarkable agreement with each other. Beyond the similarity of the atomic modulation functions across the solid solution, the structures show subtle but significant differences as a function of composition in the following ways: displacement of atom OM along the b direction and both bond-valence sum and thermal parameter mean-square displacement along c of the metal atom.

X-ray and electron diffraction study of penfieldite: average structure and multiple cells

1995 ◽  
Vol 59 (395) ◽  
pp. 341-347 ◽  
Author(s):  
S. Merlino ◽  
M. Pasero ◽  
N. Perchiazzi ◽  
A. Gianfagna
Keyword(s):  
Electron Diffraction ◽  
Diffraction Study ◽  
Direct Methods ◽  
Electron Diffraction Study ◽  
Hexagonal System ◽  
Modulated Structure ◽  
Structural Relationships ◽  
Modulated Structures ◽  
The Common ◽  
Multiple Cells

AbstractPenfieldite is a lead hydroxychloride mineral with composition Pb2Cl3(OH). It belongs to the hexagonal system, space group P, a = 11.393(3), c = 4.024(1) Å. The 4 Å c parameter corresponds to the basic sub-cell, whereas modulated structures are known with a true c axis 12 times longer. The average crystal structure of penfieldite has been solved with direct methods and refined to Rw = 0.041 for 871 refections collected with Mo-Kα radiation. The chemical and structural relationships between penfeldite and laurelite, Pb2F3(F,Cl,OH), are briefly discussed. An electron diffraction study of penfieldite revealed the occurrence, besides the common modulated structure with C = 12c, of domains with a 15c periodicity. Moreover, a 9c periodicity has been observed in crystals heated at 180°C Penfieldite is quickly destroyed above 200°C.

Sign in / Sign up

Export Citation Format

Share Document