Crystal Structures of the High Pressure Phases ZnAs and CdAs

1976 ◽  
Vol 31 (2) ◽  
pp. 158-162 ◽  
Author(s):  
J. B. Clark ◽  
Klaus-Jügen Range
Keyword(s):  
High Pressure ◽  
Crystal Structures ◽  
Normal Pressure ◽  
High Pressure Phase ◽  
Diamond Structure ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Structural Relationships ◽  
Structure Relationship ◽  
Pressure Phase

The structure of the high pressure compounds ZnAs and CdAs have been determined using Guinier film and counter methods. The compounds are orthorhombic, (space group Pbca; Z = 8), with α = 5.679(2) Å, b = 7.277(4) Å, c = 7.559(4) Å and α = 5.993(4) Å, b = 7.819(6) Å, c = 8.011(6) Å respectively.ZnAs and CdAs are isostructural with the normal pressure phases ZnSb and CdSb, which are related to the high pressure phase Si III. Structural relationships are discussed including the Si III-diamond structure relationship.

High-Pressure Synthesis and Crystal Structure of the New Orthorhombic Polymorph β-HgB4O7

2005 ◽  
Vol 60 (8) ◽  
pp. 815-820 ◽  
Author(s):  
Holger Emme ◽  
Matthias Weil ◽  
Hubert Huppertz
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Ambient Pressure ◽  
Normal Pressure ◽  
High Pressure Phase ◽  
Synthesis And Crystal Structure ◽  
Space Group ◽  
High Pressure Synthesis ◽  
Pressure Synthesis ◽  
Pressure Phase

The new orthorhombic polymorph β-HgB4O7 has been synthesized under high-pressure and hightemperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 600 °C. β-HgB4O7 is isotypic to the known ambient pressure phases MB4O7 (M = Sr, Pb, Eu) and the high-pressure phase β-CaB4O7 crystallizing with two formula units in the space group Pmn21 with lattice parameters a = 1065.6(2), b = 438.10(9), and c = 418.72(8) pm. The relation of the crystal structure of the high-pressure phase β-HgB4O7 to the normal pressure phase α-HgB4O7 as well as the relation to the isotypic phases MB4O7 (M = Sr, Pb, Eu) and β-CaB4O7 are discussed.

High-pressure phase transitions and equations of state in NiSi. III. A new high-pressure phase of NiSi

2013 ◽  
Vol 46 (1) ◽  
pp. 14-24 ◽  
Author(s):  
Ian G. Wood ◽  
Jabraan Ahmed ◽  
David P. Dobson ◽  
Lidunka Vočadlo
Keyword(s):  
Phase Diagram ◽  
High Pressure ◽  
Ab Initio ◽  
Equations Of State ◽  
Orthorhombic Phase ◽  
High Pressure Phase ◽  
Stable Phase ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Pressure Phase

A new high-pressure phase of NiSi has been synthesized in a multi-anvil press by quenching samples to room temperature from 1223–1310 K at 17.5 GPa and then recovering them to atmospheric pressure. The crystal structure of this recovered material has been determined from X-ray powder diffraction data; the resulting fractional coordinates are in good agreement with those obtained from anab initiocomputer simulation. The structure, in which each atom is six-fold coordinated by atoms of the other kind, is orthorhombic (space groupPmmn) witha= 3.27,b= 3.03,c= 4.70 Å. This orthorhombic phase of NiSi may be considered as a ferroelastic distortion of the hypothetical tetragonal (space groupP4/nmm) NiSi structure that was predicted to be the most stable phase (at 0 K) for pressures between 23 and 61 GPa in an earlierab initiostudy by Vočadlo, Wood & Dobson [J. Appl. Cryst.(2012),45, 186–196]. Furtherab initiosimulations have now shown that, with increasing pressure (at 0 K), NiSi is predicted to exist in the following polymorphs: (i) the MnP structure; (ii) the new orthorhombic structure with space groupPmmn; and (iii) the CsCl structure. Experimentally, all of these structures have now been observed and, in addition, a fourth polymorph, an ∊-FeSi-structured phase of NiSi (never the most thermodynamically stable phase in athermalab initiosimulations), may be readily synthesized at high pressure (P) and temperature (T). On the basis of both experiments and computer simulations it is therefore now clear that the phase diagram of NiSi at highPandTis complex. The simulated free-energy differences between different structures are often very small (<10 meV atom−1) and there is also the possibility of two displacive ferroelastic phase transformations, the first between structures withPmmnandP4/nmmsymmetry, and the second fromP4/nmmto a different orthorhombic phase of NiSi with space groupPbma. A complete understanding of the NiSi phase diagram (which may be of relevance to both planetary cores and the use of thin films of NiSi in semiconductor technology) can, therefore, only comevia in situexperiments at simultaneous highPand highT.

Notizen: AgNb3O8-II, eine Hochdruckphase mit neuartiger Tunnelstruktur / AgNb3O8-II, a High-Pressure Phase with a Novel Tunnel Structure Notizen

1989 ◽  
Vol 44 (4) ◽  
pp. 499-501 ◽  
Author(s):  
Klaus-Jürgen Range ◽  
Manfred Wildenauer
Keyword(s):  
High Pressure ◽  
Atmospheric Pressure ◽  
Normal Pressure ◽  
High Pressure Phase ◽  
Tunnel Structure ◽  
Pressure Phase ◽  
Type Apparatus

A quenchable high-pressure phase of AgNb3O8(AgNb3O8-II) could be synthesized at 35 kbar. 1100 °C in a modified Belt-type apparatus. The structure (Ibam, a = 7.343, b = 10.415. c = 7.007 Å , Z - 4) comprises dodecahedra NbO7 and distorted pentagonal bipyramids NbO 7 shared in such a way that elongated hexagonal tunnels along [001] are formed. Ag+-ions are situated within these tunnels. The shortest O-O distances are 2.247(11) Å (shared edges between NbO8 dodecahedra). AgNb3O8-II is metastable at atmospheric pressure and retransforms to the normal pressure phase AgNb3O8-I at 800 °C.

Darstellung und Kristallstruktur der Hochdruckphase AgAlS2-II / Preparation and Crystal Structure of the High-pressure Phase AgAlS2-II

1974 ◽  
Vol 29 (3-4) ◽  
pp. 186-189 ◽  
Author(s):  
Klaus-Jürgen Range ◽  
Gerd Engert ◽  
Armin Weiss
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Coordination Number ◽  
High Pressure Phase ◽  
Chalcopyrite Structure ◽  
Space Group ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Pressure Phase ◽  
Silver Atoms

AgAlS2-I with chalcopyrite structure transforms at 25 kbar and 300°C to the new highpressure phase AgAlS2-II. The crystal structure of AgAlS2-II is trigonal, space group P3ml, with a= 3,50 Å, c = 6,84 Å and Z = 1. The structure is based on a hexagonally close packed arrangement of sulfur atoms with aluminium atoms in octahedral sites and silver atoms in tetrahedral sites. The AgS4-tetrahedra are considerably distorted, giving a coordination number 3 + 1 for the silver atoms.

First-principles studies of phase transition and structural stability of SrC2 under pressure

2014 ◽  
Vol 28 (24) ◽  
pp. 1450190 ◽  
Author(s):  
Yi-Lin Lu ◽  
Hui Zhao
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
First Principles ◽  
Phonon Dispersion ◽  
Covalent Bond ◽  
Text Structure ◽  
High Pressure Phase ◽  
Space Group ◽  
Type Space ◽  
Pressure Phase

Pressure-induced phase transitions in SrC 2 are investigated using the first-principles plane wave pseudopotential method within the generalized gradient approximation. The phase transition from monoclinic phase ( CaC 2-II-type, space group C2/c) to trigonal ( CaC 2-VII-type, space group [Formula: see text]) structure is predicted to occur at 10.4 GPa. The high-pressure phase is thermodynamic, mechanically and dynamically stable, as verified by the calculations of its formation energy, elastic stiffness constants and phonon dispersion. Further the electronic analysis predicates this high-pressure phase to be an insulator. When increasing pressure, the ionic bond between C and Sr is strengthened, as well is the covalent bond between C and C , however, the increase of the ionic interaction between Sr and C preponderates over that of the covalent bond interaction, so the gap is narrowed.

Darstellung und Kristallstruktur der Hochdruckphase Tm2S3-II.

1976 ◽  
Vol 31 (3) ◽  
pp. 311-314 ◽  
Author(s):  
Klaus-Jürgen Range ◽  
Richard Leeb
Keyword(s):  
High Pressure ◽  
Single Crystals ◽  
High Pressure Phase ◽  
Monoclinic Space Group ◽  
Space Group ◽  
Pressure Phase

Single crystals of the quenchable high pressure phase Tm2S3-II were grown from a TmJ3-flux at 10 kbar, 1600°C. The crystals are monoclinic, space group P21/m, with a = 11.110(5) Å, b = 3.874(3) Å, c = 10.872(5) Å, β = 108.88(2)° and Z = 4. In Tm2S3-II, which is isotypic with Er3ScS6, the four independent thulium atoms are coordinated by six (2 x), seven and eight sulfur atoms.

Structure of a high-pressure phase of vanadium pentoxide, β-V2O5

2004 ◽  
Vol 60 (4) ◽  
pp. 375-381 ◽  
Author(s):  
V. P. Filonenko ◽  
M. Sundberg ◽  
P.-E. Werner ◽  
I. P. Zibrov
Keyword(s):  
High Pressure ◽  
Vanadium Pentoxide ◽  
Layer Structure ◽  
Ambient Pressure ◽  
High Pressure Phase ◽  
X Ray ◽  
Transmission Electron ◽  
Structural Relationships ◽  
Oxide Bronzes ◽  
Pressure Phase

A high-pressure phase of vanadium pentoxide, denoted β-V2O5, has been prepared at P = 6.0 GPa and T = 1073 K. The crystal structure of β-V2O5 has been studied by X-ray and neutron powder diffraction, and high-resolution transmission electron microscopy. The V atoms are six-coordinated within distorted VO6 octahedra. The structure is built up of quadruple units of edge-sharing VO6 octahedra linked by sharing edges along [010] and mutually connected by sharing corners along [001]. This arrangement forms layers of V4O10 composition in planes parallel to (100). The layers are mutually held together by weak forces. β-V2O5 is metastable and transforms to α-V2O5 at 643–653 K under ambient pressure. Structural relationships between β- and α-V2O5, and between β-V2O5 and B-Ta2O5-type structures are discussed. The high-pressure β-V2O5 layer structure can be considered as the parent of a new series of vanadium oxide bronzes with cations intercalated between the layers.

High-Pressure Phase Relations and Crystal Structures of Postspinel Phases in MgV2O4, FeV2O4, and MnCr2O4: Crystal Chemistry of AB2O4 Postspinel Compounds

2018 ◽  
Vol 57 (11) ◽  
pp. 6648-6657 ◽  
Author(s):  
Takayuki Ishii ◽  
Tsubasa Sakai ◽  
Hiroshi Kojitani ◽  
Daisuke Mori ◽  
Yoshiyuki Inaguma ◽  
...  
Keyword(s):  
High Pressure ◽  
Crystal Structures ◽  
Crystal Chemistry ◽  
Phase Relations ◽  
High Pressure Phase ◽  
Pressure Phase
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