New phase in solid nitrogen at high pressures

1985 ◽  
Vol 32 (1) ◽  
pp. 514-515 ◽  
Author(s):  
M. Grimsditch
Keyword(s):  
High Pressures ◽  
Solid Nitrogen ◽  
New Phase

Structural characterization of a new high-pressure phase of GaAsO4

2006 ◽  
Vol 62 (6) ◽  
pp. 1019-1024 ◽  
Author(s):  
David Santamaría-Pérez ◽  
Julien Haines ◽  
Ulises Amador ◽  
Emilio Morán ◽  
Angel Vegas
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
High Pressures ◽  
Ambient Conditions ◽  
Hexagonal Cell ◽  
Octahedral Sites ◽  
New Phase ◽  
Pressure Phase

As in SiO2 which, at high pressures, undergoes the α-quartz → stishovite transition, GaAsO4 transforms into a dirutile structure at 9 GPa and 1173 K. In 2002, a new GaAsO4 polymorph was found by quenching the compound from 6 GPa and 1273 K to ambient conditions. The powder diagram was indexed on the basis of a hexagonal cell (a = 8.2033, c = 4.3941 Å, V = 256.08 Å3), but the structure did not correspond to any known structure of other AXO4 compounds. We report here the ab initio crystal structure determination of this hexagonal polymorph from powder data. The new phase is isostructural to β-MnSb2O6 and it can be described as a lacunary derivative of NiAs with half the octahedral sites being vacant, but it also contains fragments of the rutile-like structure.

scholarly journals THERMODYNAMIC QUANTITIES AT HIGH PRESSURES IN THE i AND θ PHASES OF SOLID NITROGEN DEDUCED BY RAMAN FREQUENCY SHIFTS FOR THE INTERNAL MODES IN LITERATURE

2013 ◽  
Vol 27 (09) ◽  
pp. 1350035 ◽  
Author(s):  
H. YURTSEVEN ◽  
S. SARITAŞ
Keyword(s):  
Experimental Data ◽  
Thermal Expansion ◽  
Specific Heat ◽  
Pressure Dependence ◽  
Isothermal Compressibility ◽  
High Pressures ◽  
Raman Frequency ◽  
Thermodynamic Quantities ◽  
Frequency Shifts ◽  
Solid Nitrogen

The pressure dependence of the Raman frequencies of the internal modes is analyzed (T = 300 K ) for the phases i and θ of solid nitrogen using the experimental data from the literature. Through the mode Grüneisen parameter, the isothermal compressibility κT, thermal expansion αp and the specific heat Cp–Cv are calculated as a function of pressure using the Raman data in these phases. We obtain that the αp varies linearly with the (1/υ)(∂υ/∂P)T and also that the Cp–Cv varies linearly with the αp for N 2. Our results show that by means of the analysis given here, the αp, κT and Cp–Cv can be predicted from the Raman frequency shifts for the i and θ phases of solid nitrogen.

Infrared absorption of solid nitrogen at high pressures

1996 ◽  
Vol 54 (13) ◽  
pp. 8962-8964 ◽  
Author(s):  
M. D. McCluskey ◽  
L. Hsu ◽  
L. Wang ◽  
E. E. Haller
Keyword(s):  
Infrared Absorption ◽  
High Pressures ◽  
Solid Nitrogen

Prediction of amorphous structure and stability of P-N and N-CO extended solids under pressure

MRS Advances ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 95-101
Author(s):  
I.G. Batyrev
Keyword(s):  
Density Functional ◽  
High Pressures ◽  
Phonon Dispersion ◽  
Random Network ◽  
Amorphous Structure ◽  
Nitrogen And Phosphorus ◽  
Solid Nitrogen ◽  
Amorphous Network ◽  
Extended Solids ◽  
Amorphous Structures

ABSTRACTThe amorphous structures of poly-CO, P-N and N-CO extended solids at high pressures were predicted using density functional theory (DFT) and evolutionary algorithms employing variable and fixed concentrations of components methods. Compression of random network of poly-CO up to 45 GPa results in elimination of small rings of the amorphous network. The amorphous structure with stoichiometry N9P was found to be dynamically stable (no imaginary frequencies in phonon-dispersion curve), stable relative transformation to solid nitrogen and phosphorus, but metastable according to convex hull calculations. The amorphous structure of the N-CO extended solid was obtained with various concentrations of N atoms under isotropic compression up to 50 GPa and release of pressure down to 5 GPa calculated using DFT. The higher concentration of CO is found to be favourable for stabilization of an amorphous covalent N-C-O network consisting of chains and a cage of the network. Upon lowering the pressure and decomposition of the compressed extended solid, atoms are disconnected first from the ends of polymeric chains, while rings of random network are sustained almost intact. Results of a calculated Raman spectra are compared with available experimental results.

New Phase Diagram of Oxygen at High Pressures and Temperatures

2004 ◽  
Vol 93 (26) ◽  
Author(s):  
Mario Santoro ◽  
Eugene Gregoryanz ◽  
Ho-kwang Mao ◽  
Russell J. Hemley
Keyword(s):  
Phase Diagram ◽  
High Pressures ◽  
High Pressures And Temperatures ◽  
New Phase
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