scholarly journals A closer look into close packing: pentacoordinated silicon in a high-pressure polymorph of danburite

IUCrJ ◽  
2017 ◽  
Vol 4 (5) ◽  
pp. 671-677 ◽  
Author(s):  
Anna Pakhomova ◽  
Elena Bykova ◽  
Maxim Bykov ◽  
Konstantin Glazyrin ◽  
Biliana Gasharova ◽  
...  
Keyword(s):  
High Pressure ◽  
Inorganic Compounds ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
Pressure Treatment ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
High Pressure Treatment ◽  
X Ray ◽  
Unusual Formation

Due to their high technological and geological relevance, silicates are one of the most studied classes of inorganic compounds. Under ambient conditions, the silicon in silicates is almost exclusively coordinated by four oxygen atoms, while high-pressure treatment normally results in an increase in the coordination from four- to sixfold. Reported here is a high-pressure single-crystal X-ray diffraction study of danburite, CaB2Si2O8, the first compound showing a step-wise transition of Si coordination from tetrahedral to octahedral through a trigonal bipyramid. Along the compression, the Si2O7groups of danburite first transform into chains of vertice-sharing SiO5trigonal bipyramids (danburite-II) and later into chains of edge-sharing SiO6octahedra (danburite-III). It is suggested that the unusual formation of an SiO5configuration is a consequence of filling up the pentacoordinated voids in the distorted hexagonal close packing of danburite-II.

Hochdruckumwandlungen der Alkalithioindate KInS2, RbInS2 und CsInS2 / High Pressure Transformations of the Alkali thioindates KInS2, RbInS2 and CsInS2

1975 ◽  
Vol 30 (1-2) ◽  
pp. 81-87 ◽  
Author(s):  
Klaus-Jürgen Range ◽  
Günther Mahlberg
Keyword(s):  
High Pressure ◽  
Pressure Treatment ◽  
Ambient Conditions ◽  
High Pressure Treatment ◽  
X Ray ◽  
Unknown Phase

New modifications of KInS2 and RbInS2 were found after high pressure treatment and quenching to ambient conditions. The tetragonal modifications KInS2-II and RbInS2-II are isotypic with TISe. KInS2-II is metastable at all p,T-conditions investigated. The stable high pressure modification KInS2-III has a-NaFeO2-structure. Pressure treatment of CsInS2 yielded an unknown phase with a diffuse X-ray pattern.

Effect of High Pressure Treatment and Synthesis on Multiferroic Properties of 0.9BiFeO3-0.1SrTiO3 Ceramics

2014 ◽  
Vol 1082 ◽  
pp. 61-64
Author(s):  
Zheng Zheng Ma ◽  
Zi Peng Chen ◽  
Jian Qing Li ◽  
Hai Jun Huang
Keyword(s):  
High Pressure ◽  
Room Temperature ◽  
Single Phase ◽  
Pressure Treatment ◽  
X Ray Diffraction ◽  
High Pressure Treatment ◽  
X Ray ◽  
Multiferroic Properties ◽  
Pressure Synthesis ◽  
High Temperature High Pressure

The solid solution ceramics of 0.9BiFeO3-0.1SrTiO3 (BFST) were processed under cool-high pressure (BFST-H1, BFST-H2) and high temperature-high pressure (BFST-H3). And the high pressure synthesis with different temperature was used to prepare the sample BFST-H4 and BFST-H5. X-ray diffraction showed that these ceramics are almost of single phase. Among all the samples, the 3GPa,900°C high pressure synthesized one shows the optimal ferroelectricity at room temperature, with enhanced magnetic properties was observed.

Changes in the defect structure of diamond due to high temperature+ high pressure treatment

1975 ◽  
Vol 344 (1636) ◽  
pp. 111-130 ◽  
Keyword(s):  
Electron Microscopy ◽  
High Pressure ◽  
High Temperature ◽  
Optical Absorption ◽  
Defect Structure ◽  
Pressure Treatment ◽  
High Pressure Treatment ◽  
X Ray ◽  
High Temperature High Pressure ◽  
Absorption Measurements

Type la and type IIa diamonds have been heated to temperatures in the range 2000-2300 °C under a pressure of about 4.8 GPa. The changes in the defect structure of these diamonds as a result of the heat treatm ent have been examined by optical absorption measurements, integrated X-ray spike measurements and by electron microscopy. Type la diamonds changed colour from colourless to yellow after being heated for 1 min in the temperature range 2250-2300 °C and it has been shown that the yellowing was due to scattering. The scattering centres responsible were elliptically shaped cracks in the cube planes with their longest dimension in a <110> direction

High-pressure transformations of NbO2F

2000 ◽  
Vol 56 (2) ◽  
pp. 189-196 ◽  
Author(s):  
Stefan Carlson ◽  
Ann-Kristin Larsson ◽  
Franziska E. Rohrer
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
High Pressures ◽  
Ambient Pressure ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
Rietveld Refinements ◽  
X Ray ◽  
Anion Coordination ◽  
Diamond Anvil

The ReO3-type structure NbO2F, niobium dioxyfluoride, has been studied at high pressures using diamond anvil cells and synchrotron X-ray radiation. High-pressure powder diffraction measurements have been performed up to 40.1 GPa. A phase transition from the cubic (Pm3¯m) ambient pressure structure to a rhombohedral (R3¯c) structure at 0.47 GPa has been observed. Rietveld refinements at 1.38, 1.96, 3.20, 6.23, 9.00 and 10.5 GPa showed that the transition involves an a − a − a − tilting of the cation–anion coordination octahedra and a change of the anion–anion arrangement to approach hexagonal close packing. Compression and distortion of the Nb(O/F)6 octahedra is also revealed by the Rietveld refinements. At 17–18 GPa, the diffraction pattern disappears and the structure becomes X-ray amorphous.

scholarly journals The untypical high-pressure Zintl phase SrGe6

2020 ◽  
Vol 75 (1-2) ◽  
pp. 209-216 ◽  
Author(s):  
Ulrich Schwarz ◽  
Rodrigo Castillo ◽  
Julia M. Hübner ◽  
Aron Wosylus ◽  
Yurii Prots ◽  
...  
Keyword(s):  
High Pressure ◽  
Ambient Pressure ◽  
Three Dimensional ◽  
Structure Type ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Quantum Chemical Analysis ◽  
Electronic Density ◽  
X Ray ◽  
High Pressure High Temperature

AbstractThe binary strontium germanide SrGe6 was synthesized at high-pressure high-temperature conditions of approximately 10 GPa and typically 1400 K before quenching to ambient conditions. At ambient pressure, SrGe6 decomposes in a monotropic fashion at T = 680(10) K into SrGe2 and Ge, indicating its metastable character. Single-crystal X-ray diffraction data indicate that the compound SrGe6 adopts a new monoclinic structure type comprising a unique three-dimensional framework of germanium atoms with unusual cages hosting the strontium cations. Quantum chemical analysis of the chemical bonding shows that the framework consists of three- and four- bonded germanium atoms yielding the precise electron count Sr[(4bGe0]4[(3b)Ge−]2 in accordance with the 8 − N rule and the Zintl concept. Conflicting with that, a pseudo-gap in the electronic density of states appears clearly below the Fermi level, and elaborate bonding analysis reveals additional Sr–Ge interactions in the concave coordination polyhedron of the strontium atoms.

A Raman study of nylon 6 annealed under high pressure

e-Polymers ◽  
2011 ◽  
Vol 11 (1) ◽  
Author(s):  
Weijie Xu ◽  
Dahu Cao ◽  
Qiang Yu
Keyword(s):  
High Pressure ◽  
Ambient Pressure ◽  
Nylon 6 ◽  
Pressure Treatment ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
High Pressure Treatment ◽  
Structure Changes ◽  
Raman Study ◽  
Hydrogen Bonded

AbstractUsing a cubic-anvil high pressure apparatus, nylon 6 samples were annealed under 400 MPa to 1.5 GPa. The structure changes of nylon 6 are studied by the methods of wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and Raman spectra. Compared with sample prepared at ambient pressure, high pressure treatment makes the hydrogen-bonded sheets pack more closely and thus enhanced CH2 vibration out of the hydrogen-bonded sheets. After high pressure treatment, it is observed that all changes of C-C related vibration modes in nylon 6 are similar with ones in nylon series when the CH2 sequence number increased, from which it is deduced that high pressure treatment reduces the effects of amide group on the chain conformation of nylon 6.

Armstrongite at non-ambient conditions: An in-situ high-pressure single-crystal X-ray diffraction study

2019 ◽  
Vol 274 ◽  
pp. 171-175 ◽  
Author(s):  
Davide Comboni ◽  
Paolo Lotti ◽  
G. Diego Gatta ◽  
Maria Lacalamita ◽  
Ernesto Mesto ◽  
...  
Keyword(s):  
High Pressure ◽  
Single Crystal ◽  
Diffraction Study ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
X Ray

High-quality structures at high pressure? Insights from inclusions in diamonds

2016 ◽  
Vol 231 (8) ◽  
Author(s):  
Ross J. Angel ◽  
Sula Milani ◽  
Matteo Alvaro ◽  
Fabrizio Nestola
Keyword(s):  
High Pressure ◽  
Single Crystal ◽  
High Pressures ◽  
Dominant Factor ◽  
Good Precision ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Experimental Protocols ◽  
Diamond Anvil

AbstractWe describe the experimental protocols necessary to measure the crystal structures of minerals trapped within diamonds by single-crystal X-ray diffraction to the same quality as obtained from minerals studied at ambient conditions. The results show that corrections for X-ray absorption in complex cases can be made with good precision. Comparison of the refined structure of a single-crystal olivine inclusion inside a diamond with the structure of a similar olivine held in a high-pressure diamond-anvil cell shows that data resolution, not the correction for absorption effects, is the dominant factor in influencing the quality of structures determined at high pressures by single-crystal X-ray diffraction.

scholarly journals Electronic Properties and High-Pressure Behavior of Wolframite-Type CoWO4

2021 ◽  
Author(s):  
Enrico Bandiello ◽  
Placida Rodríguez-Hernandez ◽  
Alfonso Munoz ◽  
Manuel Bajo Buenestado ◽  
Catalin Popescu ◽  
...  
Keyword(s):  
High Pressure ◽  
Electronic Structure ◽  
Electronic Properties ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Pressure Behavior

In this work we characterize wolframite-type CoWO4 at ambient conditions and under compression up to 10 GPa, with emphasis on its electronic structure. X-ray diffraction and vibrational experiments, supported by...

Crystal Structure Refinements of Ge(tP12), Physical Properties and Pressure-induced Phase Transformation Ge(tP12) ↔ Ge(tI4)

2008 ◽  
Vol 63 (6) ◽  
pp. 608-614 ◽  
Author(s):  
Aron Wosylus ◽  
Yurii Prots ◽  
Walter Schnelle ◽  
Michael Hanfland ◽  
Ulrich Schwarz
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Theoretical Calculations ◽  
Structural Similarity ◽  
Phase Region ◽  
Maximum Pressure ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Two Phase ◽  
X Ray

Single crystals of the modification Ge(tP12) are prepared by compressing semiconductor-grade germanium to pressures above 11(1) GPa and heating to temperatures between 1200(100) and 1500(150) K before a stepwise cooling precedes a complete pressure release. The tetragonal crystal structure of Ge(tP12) is refined by means of single crystal X-ray diffraction data collected at ambient conditions (a = 592.81(2), c = 698.03(3) pm, space group P43212). The atomic arrangement comprising interconnected spiral chains of fourfold symmetry bears a structural similarity to the high-pressure modification S(t I16). High-pressure ambient-temperature powder X-ray diffraction measurements reveal a significant anisotropy of the compressibility compatible with the selected crystal structure description. The determined bulk modulus of Ge(tP12) amounts to 70(1) GPa which is in good agreement with theoretical calculations and similar to experimental values of other four-coordinated germanium allotropes. Ge(tP12) is a diamagnetic semiconductor with χ0 = −3.1(3) ·10−7 emu g−1 and ρ300 K ≈ 6 Ωm at 300 K. At 10.1(3) GPa, the beginning of the formation of Ge(t I 4) indicates the onset of a structural transition. The two-phase region extends up to a maximum pressure of 13.0(5) GPa in the direction of increasing pressures. Upon stepwise decompression, the phase Ge(t P12) is reformed from Ge(t I4) at 9(1) GPa.

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