Disorder–order structural transition of single crystal hydrogen chloride under high pressure–temperature

High-pressure single-crystal synchrotron X-ray diffraction data for galenobismutite, PbBi2S4 collected up to 20.9 GPa, were fitted by a third-order Birch-Murnaghan equation of state, as suggested by a FE-fE plot, yielding V0 = 697.4(8) Å3, K0 = 51(1) GPa and K’ = 5.0(2). The axial moduli were M0a = 115(7) GPa and Ma’ = 28(2) for the a axis, M0b = 162(3) GPa and Mb’ = 8(3) for the b axis, M0c = 142(8) GPa and Mc’ = 26(2) for the c axis, with refined values of a0, b0, c0 equal to 11.791(7) Å, 14.540(6) Å 4.076(3) Å, respectively, and a ratio equal to M0a:M0b:M0c = 1.55:1:1.79. The main structural changes on compression were the M2 and M3 (occupied by Bi, Pb) movements toward the centers of their respective trigonal prism bodies and M3 changes towards CN8. The M1 site, occupied solely by Bi, regularizes the octahedral form with CN6. The eccentricities of all cation sites decreased with compression testifying for a decrease in stereochemical expression of lone electron pairs. Galenobismutite is isostructural with calcium ferrite CaFe2O4, the suggested high pressure structure can host Na and Al in the lower mantle. The study indicates that pressure enables the incorporation of other elements in this structure, increasing its potential significance for mantle mineralogy.

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Investigation of the crystal structure of a low water content hydrous olivine to 29.9 GPa: A high-pressure single-crystal X-ray diffraction study

American Mineralogist ◽

10.2138/am-2020-7444 ◽

2020 ◽

Vol 105 (12) ◽

pp. 1857-1865

Author(s):

Jingui Xu ◽

Dawei Fan ◽

Dongzhou Zhang ◽

Bo Li ◽

Wenge Zhou ◽

...

Keyword(s):

High Pressure ◽

Equation Of State ◽

Single Crystal ◽

Water Content ◽

Structural Changes ◽

Volume Data ◽

Structural Refinement ◽

X Ray Diffraction ◽

X Ray ◽

Water Contents

Abstract Olivine is the most abundant mineral in the Earth's upper mantle and subducting slabs. Studying the structural evolution and equation of state of olivine at high-pressure is of fundamental importance in constraining the composition and structure of these regions. Hydrogen can be incorporated into olivine and significantly influence its physical and chemical properties. Previous infrared and Raman spectroscopic studies indicated that local structural changes occur in Mg-rich hydrous olivine (Fo ≥ 95; 4883–9000 ppmw water) at high-pressure. Since water contents of natural olivine are commonly <1000 ppmw, it is inevitable to investigate the effects of such water contents on the equation of state (EoS) and structure of olivine at high-pressure. Here we synthesized a low water content hydrous olivine (Fo95; 1538 ppmw water) at low SiO2 activity and identified that the incorporated hydrogens are predominantly associated with the Si sites. We performed high-pressure single-crystal X-ray diffraction experiments on this olivine to 29.9 GPa. A third-order Birch-Murnaghan equation of state (BM3 EoS) was fit to the pressure-volume data, yielding the following EoS parameters: VT0 = 290.182(1) Å3, KT0 = 130.8(9) GPa, and K′T0 = 4.16(8). The KT0 is consistent with those of anhydrous Mg-rich olivine, which indicates that such low water content has negligible effects on the bulk modulus of olivine. Furthermore, we carried out the structural refinement of this hydrous olivine as a function of pressure to 29.9 GPa. The results indicate that, similar to the anhydrous olivine, the compression of the M1-O and M2-O bonds are comparable, which are larger than that of the Si-O bonds. The compression of M1-O and M2-O bonds of this hydrous olivine are comparable with those of anhydrous olivine, while the Si-O1 and Si-O2 bonds in the hydrous olivine are more compressible than those in the anhydrous olivine. Therefore, this study suggests that low water content has negligible effects on the EoS of olivine, though the incorporation of water softens the Si-O1 and Si-O2 bond.

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Crystal structure of the high-pressure phase of the oxonitridosilicate chloride Ce4[Si4O3 + x N7 − x ]Cl1 − x O x , x ≃ 0.2

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768106003302 ◽

2006 ◽

Vol 62 (2) ◽

pp. 205-211 ◽

Cited By ~ 1

Author(s):

Alexandra Friedrich ◽

Eiken Haussühl ◽

Wolfgang Morgenroth ◽

Alexandra Lieb ◽

Björn Winkler ◽

...

Keyword(s):

Phase Transition ◽

High Pressure ◽

Single Crystal ◽

Structural Changes ◽

Low Pressure ◽

First Order Phase Transition ◽

Compression Mechanism ◽

Diamond Anvil ◽

Structural Mechanisms ◽

First Order Phase

The structural compression mechanism of Ce4[Si4O3 + x N7 − x ]Cl1 − x O x , x ≃ 0.2, was investigated by in situ single-crystal synchrotron X-ray diffraction at pressures of 3.0, 8.5 and 8.6 GPa using the diamond–anvil cell technique. On increasing pressure the low-pressure cubic structure first undergoes only minor structural changes. Between 8.5 and 8.6 GPa a first-order phase transition occurs, accompanied by a change of the single-crystal colour from light orange to dark red. The main structural mechanisms, leading to a volume reduction of about 5% at the phase transition, are an increase in and a rearrangement of the Ce coordination, the loss of the Ce2, Ce3 split position, and a bending of some of the inter-polyhedral Si—N—Si angles in the arrangement of the corner-sharing Si tetrahedra. The latter is responsible for the short c axis of the orthorhombic high-pressure structure compared with the cell parameter of the cubic low-pressure structure.

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Structural and electronic behaviour of MoS2, MoSe2and MoTe2at high pressure

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273314083806 ◽

2014 ◽

Vol 70 (a1) ◽

pp. C1619-C1619

Author(s):

Liliana Grajcarova ◽

Michaela Riflikova ◽

Roman Martonak ◽

Erio Tosatti

Keyword(s):

High Pressure ◽

Electronic Transition ◽

Structural Changes ◽

Structural Transition ◽

Transition Metal Dichalcogenides ◽

X Ray Diffraction ◽

X Ray ◽

Excitonic Insulator ◽

Metal Dichalcogenides ◽

Indirect Band Gap

Using ab initio calculations and metadynamics simulations we studied the behaviour of layered semiconducting transition metal dichalcogenides, MoX2 (X = S, Se, Te) at high pressure with focus on structural transitions and metallization [1,2]. We found that concerning structure, the behaviour of MoS2 is different from that of MoSe2 and MoTe2. In MoS2 pressure induces at 20 GPa a structural transition where layer sliding takes place, bringing the initial 2Hc stacking to a 2Ha stacking typical of e.g. 2H-NbSe2. This finding naturally explains previous X-ray diffraction and Raman spectroscopy data and was very recently confirmed by new X-ray diffraction experiments[3]. On the other hand, this transition does not occur in MoSe2 and MoTe2 where instead the initial 2Hc stacking remains stable. Besides structural changes pressure in MoS2 induces also a semiconductor - semimetal transition which takes place by band overlap and closing of indirect band gap. This electronic transition occurs in the same region where the structural transition takes place, at 25 GPa in the 2Hc phase and at 20 GPa in the 2Ha phase. In case of MoSe2 and MoTe2 a very similar electronic transition leading to semimetal is predicted to occur at 28 GPa and 13 GPa, respectively. All three materials exhibit after metallization a low density of states at the Fermi level implying low superconducting temperature (if any). Due to absence of structural transition in the metallization region MoSe2 and MoTe2 could be suitable candidate materials for observation of the excitonic insulator phase.

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Single Crystal Growth of High-Pressure Phases of Ice and Salt Hydrate Far Below the Original Melting Point by Mixing Alcohol: Crystal Structure Determination of Magnesium Chloride Heptahydrate

10.26434/chemrxiv.11345063.v2 ◽

2020 ◽

Author(s):

Keishiro Yamashita ◽

Kazuki Komatsu ◽

Hiroyuki Kagi

Keyword(s):

Crystal Structure ◽

High Pressure ◽

Crystal Growth ◽

Single Crystal ◽

Room Temperature ◽

Growth Technique ◽

Salt Hydrate ◽

X Ray

An crystal-growth technique for single crystal x-ray structure analysis of high-pressure forms of hydrogen-bonded crystals is proposed. We used alcohol mixture (methanol: ethanol = 4:1 in volumetric ratio), which is a widely used pressure transmitting medium, inhibiting the nucleation and growth of unwanted crystals. In this paper, two kinds of single crystals which have not been obtained using a conventional experimental technique were obtained using this technique: ice VI at 1.99 GPa and MgCl<sub>2</sub>·7H<sub>2</sub>O at 2.50 GPa at room temperature. Here we first report the crystal structure of MgCl2·7H2O. This technique simultaneously meets the requirement of hydrostaticity for high-pressure experiments and has feasibility for further in-situ measurements.

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Single Crystal Growth and Physical Properties of Pyroxene CoGeO3

Crystals ◽

10.3390/cryst11040378 ◽

2021 ◽

Vol 11 (4) ◽

pp. 378

Author(s):

Li Zhao ◽

Zhiwei Hu ◽

Hanjie Guo ◽

Christoph Geibel ◽

Hong-Ji Lin ◽

...

Keyword(s):

High Pressure ◽

Magnetic Properties ◽

Magnetic Susceptibility ◽

Crystal Growth ◽

Physical Properties ◽

Single Crystal ◽

Single Crystals ◽

Magnetic Moments ◽

Single Crystal Growth ◽

The Impact

We report on the synthesis and physical properties of cm-sized CoGeO3 single crystals grown in a high pressure mirror furnace at pressures of 80 bar. Direction dependent magnetic susceptibility measurements on our single crystals reveal highly anisotropic magnetic properties that we attribute to the impact of strong single ion anisotropy appearing in this system with TN∼33.5 K. Furthermore, we observe effective magnetic moments that are exceeding the spin only values of the Co ions, which reveals the presence of sizable orbital moments in CoGeO3.

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