Farneseite, a new mineral of the cancrinite - sodalite group with a 14-layer stacking sequence: occurrence and crystal structure

AbstractTwo quintinite polytypes, 3R and 2T, which are new for the Kovdor alkaline-ultrabasic complex, have been structurally characterized. The crystal structure of quintinite-2T was solved by direct methods and refined to R1 = 0.048 on the basis of 330 unique reflections. The structure is trigonal, P$\bar 3$c1, a = 5.2720(6), c = 15.113(3) Å and V = 363.76(8) Å3. The crystal structure consists of [Mg2Al(OH)6]+ brucite-type layers with an ordered distribution of Mg2+ and Al3+ cations according to the $\sqrt 3 $ × $\sqrt 3 $ superstructure with the layers stacked according to a hexagonal type. The complete layer stacking sequence can be described as …=Ab1C = Cb1A=…. The crystal structure of quintinite-3R was solved by direct methods and refined to R1 = 0.022 on the basis of 140 unique reflections. It is trigonal, R$\bar 3$m, a = 3.063(1), c = 22.674(9) Å and V = 184.2(1) Å3. The crystal structure is based upon double hydroxide layers [M2+,3+(OH)2] with disordered distribution of Mg, Al and Fe and with the layers stacked according to a rhombohedral type. The stacking sequence of layers can be expressed as …=АB = BC = CA=… The study of morphologically different quintinite generations grown on one another detected the following natural sequence of polytype formation: 2H → 2T → 1M that can be attributed to a decrease of temperature during crystallization. According to the information-based approach to structural complexity, this sequence corresponds to the increasing structural information per atom (IG): 1.522 → 1.706 → 2.440 bits, respectively. As the IG value contributes negatively to the configurational entropy of crystalline solids, the evolution of polytypic modifications during crystallization corresponds to the decreasing configurational entropy. This is in agreement with the general principle that decreasing temperature corresponds to the appearance of more complex structures.

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Zincalstibite-9R: the first nine-layer polytype with the layered double hydroxide structure-type

Mineralogical Magazine ◽

10.1180/minmag.2012.076.5.01 ◽

2012 ◽

Vol 76 (5) ◽

pp. 1337-1345 ◽

Cited By ~ 13

Author(s):

S. J. Mills ◽

A. G. Christy ◽

A. R. Kampf ◽

R. M. Housley ◽

G. Favreau ◽

...

Keyword(s):

Crystal Structure ◽

Layered Double Hydroxide ◽

Structure Type ◽

Refractive Indices ◽

Stacking Sequence ◽

Oh Groups ◽

Layer Stacking ◽

Periodic Layer ◽

Double Hydroxide ◽

The Ideal

AbstractZincalstibite-9R, a new polytype in the hydrotalcite supergroup is reported from the Monte Avanza mine, Italy. It occurs as pale blue curved disc-like tablets flattened on {001} intergrown to form rosettes typically less than 50 μm in diameter, with cyanophyllite and linarite in cavities in baryte. Zincalstibite-9R is uniaxial (–), with refractive indices ω = 1.647(2) and ε = 1.626(2) measured in white light. The empirical formula (based on 12 OH groups) is (Zn1.092+Cu0.872+Al0.04)Σ2.00Al1.01(Sb0.975+Si0.02)Σ0.99(OH)12, and the ideal formula is (Zn,Cu)2Al(OH)6[Sb(OH)6]. Zincalstibite-9R crystallizes in space group R, with a = 5.340(2), c = 88.01(2) Å, V = 2173.70(15) Å3 and Z = 9. The crystal structure was refined to R1 = 0.0931 for 370 unique reflections [Fo > 4σ(F)] and R1 = 0.0944 for all 381 unique reflections. It has the longest periodic layer stacking sequence for a layered double hydroxide compound reported to date.

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Crystal chemistry of natural layered double hydroxides. I. Quintinite-2H-3c from the Kovdor alkaline massif, Kola peninsula, Russia

Mineralogical Magazine ◽

10.1180/minmag.2010.074.5.821 ◽

2010 ◽

Vol 74 (5) ◽

pp. 821-832 ◽

Cited By ~ 28

Author(s):

S. V. Krivovichev ◽

V. N. Yakovenchuk ◽

E. S. Zhitova ◽

A. A. Zolotarev ◽

Y. A. Pakhomovsky ◽

...

Keyword(s):

Crystal Structure ◽

Kola Peninsula ◽

Direct Methods ◽

Stacking Sequence ◽

Layer Sequence ◽

Layer Stacking ◽

Double Hydroxide ◽

Double Hydroxides ◽

First Time ◽

Alkaline Massif

AbstractThe crystal structure of quintinite-2H-3c, [Mg4Al2(OH)12](CO3)(H2O)3, from the Kovdor alkaline massif, Kola peninsula, Russia, was solved by direct methods and refined to an agreement index (R1) of 0.055 for 484 unique reflections with |Fo| ≥ 4σF. The mineral is rhombohedral, R32, a = 5.2745(7), c = 45.36(1) Å. The diffraction pattern of the crystal has strong and sharp Bragg reflections having h–k = 3n and l = 3n and lines of weak superstructure reflections extended parallel to c* and centred at h–k ≠ 3n. The structure contains six layers within the unit cell with the layer stacking sequence of …AC=CA=AC=CA=AC=CA… The Mg and Al atoms are ordered in metal hydroxide layers to form a honeycomb superstructure. The full superstructure is formed by the combination of two-layer stacking sequence and Mg-Al ordering. This is the first time that a long-range superstructure in carbonate-bearing layered double hydroxide (LDH) has been observed. Taking into account Mg-Al ordering, the unique layer sequence can be written as …=Ab1C=Cb1A=Ab2C=Cb2A=Ab3C=Cb3A=… The use of an additional suffix is proposed in order to distinguish between LDH polytypes having the same general stacking sequence but with different c parameters compared with the ‘standard’ polytype. According to this notation, the quintinite studied here can be described as quintinite-2H-3c or quintinite-2H-3c[6R], indicating the real symmetry.

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

Crystallography Reports ◽

10.1134/1.1780629 ◽

2004 ◽

Vol 49 (4) ◽

pp. 635-642 ◽

Cited By ~ 9

Author(s):

K. A. Rozenberg ◽

A. N. Sapozhnikov ◽

R. K. Rastsvetaeva ◽

N. B. Bolotina ◽

A. A. Kashaev

Keyword(s):

Crystal Structure ◽

Stacking Sequence ◽

Layer Stacking

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Polytypism, polymorphism, and superconductivity in TaSe2−xTex

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1502460112 ◽

2015 ◽

Vol 112 (11) ◽

pp. E1174-E1180 ◽

Cited By ~ 50

Author(s):

Huixia Luo ◽

Weiwei Xie ◽

Jing Tao ◽

Hiroyuki Inoue ◽

András Gyenis ◽

...

Keyword(s):

Crystal Structure ◽

Physical Properties ◽

Single Layer ◽

Large Family ◽

Layered Materials ◽

Stacking Sequence ◽

Superconducting Transition ◽

Surprising Effect ◽

Layer Stacking ◽

Structural Layer

Polymorphism in materials often leads to significantly different physical properties—the rutile and anatase polymorphs of TiO2 are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer-stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivity of TaSe2, one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access two stable polytypes and two stable polymorphs in the TaSe2−xTex solid solution and find that the 3R polytype shows a superconducting transition temperature that is between 6 and 17 times higher than that of the much more commonly found 2H polytype. The reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of Tc on subtle differences in the characteristics of the single layers present or from a surprising effect of the layer-stacking sequence on electronic properties that are typically expected to be dominated by the properties of a single layer in materials of this kind.

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Stacking sequences of the crystallites in Co-Sm films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100166038 ◽

1996 ◽

Vol 54 ◽

pp. 714-715

Author(s):

B. W. Robertson ◽

Y. Liu

Keyword(s):

Crystal Structure ◽

Equilibrium Phase ◽

High Resolution Electron Microscopy ◽

Magnetic Thin Films ◽

Equilibrium Phase Diagram ◽

Stacking Sequence ◽

Close Packed Structure ◽

Resolution Electron ◽

Layer Stacking ◽

Packed Structure

Magnetic thin films sputtered from the Co-Sm system have been shown to be promising as recording media. High coercivities of up to 4.0 kOe have been obtained from Co-Sm films. Recent microstructure characterization of Co-Sm films deposited by the DC magnetron sputtering has shown that the microstructure is composed of the amorphous matrix and crystallites with a grain size of about 5nm . As different sputtering processes have different dynamics for the formation of the nanostructure, phases formed could be different from those predicted by the equilibrium phase diagram. Crystal structure determination is important for understanding the high anisotropy and epitaxy growth of the Co-Sm films. The crystal structure of the crystallites was identified to be a close-packed structure. However, the stacking sequence changes from crystallite to crystallite. This paper describes the detailed high resolution electron microscopy (HREM) study of the stacking sequence of the crystallites in Co-Sm films. It is found that the stacking near the Cr underlayer tends to be hexagonal (ABAB) stacking. As the film grows, the stacking sequence is disturbed and three layer stacking, four layer stacking and random stacking are formed.

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Two Astrophyllite-Supergroup Minerals: Bulgakite, A New Mineral From the Darai-Pioz Alkaline Massif, Tajikistan and Revision of the Crystal Structure and Chemical Formula of Nalivkinite

The Canadian Mineralogist ◽

10.3749/canmin.1500085 ◽

2016 ◽

Vol 54 (1) ◽

pp. 33-48 ◽

Cited By ~ 8

Author(s):

Atali A. Agakhanov ◽

Leonid A. Pautov ◽

Elena Sokolova ◽

Yassir A. Abdu ◽

Vladimir Y. Karpenko

Keyword(s):

Crystal Structure ◽

New Mineral ◽

Chemical Formula ◽

Alkaline Massif

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Shimazakiite-4M and shimazakiite-4O, Ca2B2O5, two polytypes of a new mineral from Fuka, Okayama Prefecture, Japan

Mineralogical Magazine ◽

10.1180/minmag.2013.077.1.09 ◽

2013 ◽

Vol 77 (1) ◽

pp. 93-105 ◽

Cited By ~ 10

Author(s):

I. Kusachi ◽

S. Kobayashi ◽

Y. Takechi ◽

Y. Nakamuta ◽

T. Nagase ◽

...

Keyword(s):

Crystal Structure ◽

Diffraction Pattern ◽

Powder Diffraction ◽

Refractive Indices ◽

New Mineral ◽

Calcium Borate ◽

Crystalline Limestone ◽

Okayama Prefecture

AbstractShimazakiite occurs as greyish white aggregates up to 3 mm in diameter. Two polytypes, shimazakiite-4M and shimazakiite-4O, have been identified, the former in nanometre-sized twin lamellae and the latter in micrometre-sized lamellae. Shimazakiite was discovered in an irregular vein in crystalline limestone near gehlenite-spurrite skarns at Fuka mine, Okayama Prefecture, Japan. Associated minerals include takedaite, sibirskite, olshanskyite, parasibirskite, nifontovite, calcite and an uncharacterized hydrous calcium borate. The mineral is biaxial (–), with the following refractive indices (at 589 nm): α = 1.586(2), β = 1.650(2), γ = 1.667(2) and 2Vcalc = 53º [shimazakiite-4M]; and α = 1.584(2), β = 1.648(2), γ = 1.670(2) and 2Vcalc = 54.88º [shimazakiite-4O]. Quantitative electronmicroprobe analyses (means of 28 and 25 determinations) gave the empirical formulae Ca2B1.92O4.76(OH)0.24 and Ca2B1.92O4.76(OH)0.24 for shimazakiite-4M and shimazakiite-4O, respectively. The crystal structure refinements: P21/c, a = 3.5485(12), b = 6.352(2), c = 19.254(6) Å , β = 92.393(13)°, V = 433.6(3) Å3 [for shimazakiite-4M]; and P212121, a = 3.55645(8), b = 6.35194(15), c = 19.2534(5) Å , V = 434.941(18) Å3[for shimazakiite-4O], converged into R1 indices of 0.1273 and 0.0142, respectively. The crystal structure of shimazakiite consists of a layer containing B2O5 units (two near-coplanar triangular corner-sharing BO3 groups) and 6- and 7-coordinate Ca atoms. Different sequences in the c direction of four layers are observed in the polytypes. The five strongest lines in the powder-diffraction pattern [listed as d in Å (I)(hkl)] are: 3.02(84)(022); 2.92(100)(10) 2.81(56)(104); 2.76(32)(113); 1.880(32)(11,12,126,118) [for shimazakiite-4M]; and 3.84(33)(014); 3.02(42)(022); 2.86(100)(104); 2.79(29)(113); 1.903(44)(126,118) [for shimazakiite-4O].

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