Crystal structure of anhydrous phase X, K1.93(Mg2.02Cr0.02)Si2.00O7

Matsuzaki, Takashi; Hagiya, Kenji; Shatskiy, Anton; Katsura, Tomoo; Matsui, Masanao

doi:10.2465/jmps.090321

Cited by 16 publications

(18 citation statements)

References 21 publications

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“…The [KO 9 ] polyhedra share rectangular faces with an area of about 12⋅10 4 pm 2 . This structural motif had been reported for BaFe 4 O 7 and K 0.22 Ba 0.89 Fe 4 O 7 as well as for the high pressure phases A 2 Mg 2 Si 2 O 7 ( A =Na, K) ,…”

Section: Resultssupporting

confidence: 75%

Oxo‐Hydroxoferrate K_2−xFe₄O_7−x(OH)_x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures

et al. 2019

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The reaction of Fe(NO3)3⋅9 H2O with KOH under hydroflux conditions at about 200 °C produces red crystals of K2−xFe4O7−x(OH)x in a quantitative yield. In the crystal structure, edge‐sharing [FeO6] octahedra form ∞2[ Fe2O6] honeycomb nets. Pillars consisting of pairs of vertex‐sharing [FeO4] tetrahedra link the honeycomb layers and form columnar halls in which the potassium ions are located. The trigonal (P true3‾ 1m) and the hexagonal (P63/mcm) polytypes of K2−xFe4O7−x(OH)x show oriented intergrowth. The sub‐stoichiometric potassium content (x≈0.3) is compensated by hydroxide ions. K2−xFe4O7−x(OH)x is an antiferromagnet above 2 K and its magnetic structure was determined by neutron powder diffraction. Under ambient conditions, K2−xFe4O7−x(OH)x hydrolyzes and K2CO3 ⋅ H2O forms gradually on the surface of the K2−xFe4O7−x(OH)x crystals. Upon annealing at air at about 500 °C, the potassium atoms in the columnar halls start to order into a superstructure. The thermal decomposition of K2−xFe4O7−x(OH)x proceeds via a topotactic transformation into K1+x′Fe11O17, adopting the rhombohedral β’’ or the hexagonal β‐aluminate‐type structure, before γ‐Fe2O3 is formed above 950 °C, which then converts into thermodynamically stable α‐Fe2O3.

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Section: Resultssupporting

confidence: 75%

Oxo‐Hydroxoferrate K_2−xFe₄O_7−x(OH)_x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures

et al. 2019

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“…Two alternative structures for anhydrous-PhX, K 2 Mg 2 Si 2 O 7 , have been reported: a one-layer structure having the centrosymmetric space group P31m (Matsuzaki et al 2010), and a twolayer structure having the non-centrosymmetric space group P6 3 cm (Yang et al 2001;Mancini et al 2002). Until the study of Matsuzaki et al (2010), the trigonal structure had only been found for anhydrous sodic-PhX, ideally Na 2 Mg 2 Si 2 O 7 (Yang et al 2001).…”

Section: Introductionmentioning

confidence: 95%

“…Until the study of Matsuzaki et al (2010), the trigonal structure had only been found for anhydrous sodic-PhX, ideally Na 2 Mg 2 Si 2 O 7 (Yang et al 2001).…”

Section: Introductionmentioning

confidence: 98%

New structural features of the high-pressure synthetic sheet-disilicate Phase-X, K(2-x)Mg2Si2O7Hx

Welch

Konzett

Bindi

et al. 2012

American Mineralogist

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The structure of the synthetic high-pressure sheet-disilicate Phase-X (PhX), a possible host of H 2 O and K in the mantle, has been determined for a crystal synthesized at 16 GPa/1300 °C/23 h. The composition of the sample is close to K 1.5 Mg 2 Si 2 O 7 H 0.5 , which is 50% PhX/50% Anhydrous-PhX and has 25% of interlayer K sites vacant. The structures of four crystals were determined by singlecrystal X-ray diffraction and had very similar diffraction characteristics and structural results; the structure of one of the larger crystals is reported here. Reflection intensity statistics strongly indicate that PhX is centrosymmetric, space group P6 3 /mcm, in contrast to other studies that have reported non-centrosymmetric space group P6 3 cm. While it was possible to obtain good agreement indices for refinements in P6 3 cm, there were strong correlations between atoms that are equivalent in P6 3 /mcm, suggesting that the correct structure is centrosymmetric. Full anisotropic refinement in space group P6 3 /mcm gave R 1 = 0.036, wR 2 = 0.079, GoF = 1.467. As with all previous studies of PhX, the H atom was not located. Difference-Fourier maps of the residual electron density indicated that the K atom is displaced from the 4c site lying on the sixfold axis on to three split 12j sites 0.2 Å away, each having ¼ occupancy, giving a total of 3 K atoms per unit cell and corresponding to 1.5 K apfu, in good agreement with the content derived from electron microprobe analysis. Diffraction patterns of all four crystals examined, reconstructed from the full-intensity data collection, consistently show the presence of a large hexagonal superstructure with dimensions 8a sub × 8a sub × c sub , having Z = 128, compared with Z = 2 for the two-layer subcell. Complex arrays of superlattice reflections occur in layers with l = 2n, but are absent from l = 2n + 1 layers.Unpolarized infrared spectra of single crystals of PhX were obtained that are similar to those reported previously in the literature. Spectra in the OH-stretching region consist of a major absorption band at 3595 cm -1 and three much weaker bands at 3690, 3560, and 3405 cm -1 . Bond-valence analysis of PhX indicates that O1 is very over-bonded, whereas O2 is slightly under-bonded and a possible site for protonation. We present geometrical and crystal-chemical arguments that exclude O1 as a candidate for protonation, whereas a much better case can be made for O2. In PhX structures, H must be located at a partially occupied site with a multiplicity 4 ≤ m ≤ 24 in P6 3 /mcm or 4 ≤ m ≤ 12 in P6 3 cm. Such low occupancies for H sites are the likely reason for their invisibility to diffraction. We outline a model for the incorporation of H into PhX of composition K 1.5 Mg 2 Si 2 O 7 H 0.5 that suggests a mechanism for ordering based upon avoidance of H and K, coupled with K-site vacancies. Such behavior may also be the origin of the superstructure. The P6 3 /mcm structure and the presence of an underlying superstructure may well be characteristic of ordered intermediate composit...

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“…In order to find structurally related compounds one may start with other silicates having a similar chemical formula of the type [50]. However, the majority of these materials do not exhibit a closer relationship with the present compound.…”

Section: Discussion and Comparison With Related Structuresmentioning

confidence: 96%

Li2Ca2Si2O7: Structural, spectroscopic and computational studies on a sorosilicate

Kahlenberg

Brunello

Hejny

et al. 2015

Journal of Solid State Chemistry

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Crystal structure of anhydrous phase X, K1.93(Mg2.02Cr0.02)Si2.00O7

Cited by 16 publications

References 21 publications

Oxo‐Hydroxoferrate K_2−xFe₄O_7−x(OH)_x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures

Oxo‐Hydroxoferrate K_2−xFe₄O_7−x(OH)_x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures

New structural features of the high-pressure synthetic sheet-disilicate Phase-X, K(2-x)Mg2Si2O7Hx

Li2Ca2Si2O7: Structural, spectroscopic and computational studies on a sorosilicate

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Crystal structure of anhydrous phase X, K1.93(Mg2.02Cr0.02)Si2.00O7

Cited by 16 publications

References 21 publications

Oxo‐Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures

Oxo‐Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures

New structural features of the high-pressure synthetic sheet-disilicate Phase-X, K(2-x)Mg2Si2O7Hx

Li2Ca2Si2O7: Structural, spectroscopic and computational studies on a sorosilicate

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Oxo‐Hydroxoferrate K_2−xFe₄O_7−x(OH)_x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures

Oxo‐Hydroxoferrate K_2−xFe₄O_7−x(OH)_x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures