scholarly journals Pressure-induced structural phase transformation in cobalt(II) dicyanamide

2015 ◽  
Vol 71 (3) ◽  
pp. 252-257 ◽  
Author(s):  
Andrey A. Yakovenko ◽  
Karena W. Chapman ◽  
Gregory J. Halder
Keyword(s):  
High Pressures ◽  
Structural Phase ◽  
Maximum Pressure ◽  
Structural Distortions ◽  
Synchrotron Powder Diffraction ◽  
Measured Pressure ◽  
Pressure Phase ◽  
Molecular Framework

In situsynchrotron powder diffraction has been used to probe the pressure-dependent structural properties of the magnetic molecular framework material Co(dca)2[dca = dicyanamide or N(CN)2−]. An orthorhombic (Pmnn) to monoclinic (P21/n) transformation to a high-pressure phase, namely γ-Co(dca)2, occurs at 1.1 GPa. Structural determination of γ-Co(dca)2shows that the rutile-like topology of the pristine material is retained at high pressures, with the lower symmetry allowing a progression of volume-reducing structural distortions. γ-Co(dca)2was stable at the maximum pressure measured of 4.2 GPa. Both phases were soft, with bulk moduli (B0) for α-Co(dca)2and γ-Co(dca)2of 13.15 (18) and 9.0 (6) GPa, respectively. Modest uniaxial negative linear compressibility (K) of the order of −4 TPa−1was observed over the entire measured pressure range.

High-Pressure Phase Transitions of Cubic Y 2 O 3 under High Pressures by In-situ Synchrotron X-Ray Diffraction

2019 ◽  
Vol 36 (4) ◽  
pp. 046103 ◽  
Author(s):  
Sheng Jiang ◽  
Jing Liu ◽  
Xiao-Dong Li ◽  
Yan-Chun Li ◽  
Shang-Ming He ◽  
...  
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
High Pressures ◽  
High Pressure Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Pressure Phase

In situ structure determination of the high-pressure phase of Fe3O4

1999 ◽  
Vol 84 (1-2) ◽  
pp. 203-206 ◽  
Author(s):  
Yingwei Fei ◽  
Daniel J. Frost ◽  
Ho-Kwang Mao ◽  
Charles T. Prewitt ◽  
Daniel Haeusermann
Keyword(s):  
High Pressure ◽  
Structure Determination ◽  
High Pressure Phase ◽  
Pressure 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.

Determination of the crystal structure of nifedipine form C by synchrotron powder diffraction

2011 ◽  
Vol 67 (4) ◽  
pp. 357-364 ◽  
Author(s):  
Mauro Bortolotti ◽  
Ivan Lonardelli ◽  
Giancarlo Pepponi
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Molecular Conformation ◽  
Thermal Characterization ◽  
Powder Diffraction Data ◽  
Synchrotron Powder Diffraction ◽  
Metastable Form

The crystal structure of the metastable form C polymorph of nifedipine [C17H18N2O6, 3,5-dimethyl 2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate] was determined by means of direct-space techniques applied to high-resolution synchrotron powder diffraction data. The polymorph crystallizes in the space group P\bar 1 and exhibits a molecular packing significantly different from that of the stable modification, with molecules aligned in an orthogonal configuration inside the unit cell. The molecular conformation, on the other hand, remains substantially unmodified between the two polymorphs. Additionally, in situ thermal characterization of nifedipine crystallization behaviour was performed, confirming the nucleation of another metastable polymorph (form B) prior to the complete crystallization of the stable modification. A complete structural characterization of form B was not possible owing to its very limited stability interval.

A Model of Strain Distribution in Nanocrystalline SiC and Diamond at Very High Pressures; In-Situ X-RAY Diffraction Study and Computer Modelling

1998 ◽  
Vol 538 ◽  
Author(s):  
R. Pielaszek ◽  
B. Palosz ◽  
S. Gierlotka ◽  
S. Stel'Makh ◽  
U. Bismayer
Keyword(s):  
High Pressures ◽  
Computer Modelling ◽  
Nanocrystalline Silicon ◽  
X Ray Diffraction ◽  
Nanocrystalline Silicon Carbide ◽  
Structure And Microstructure ◽  
Very High ◽  
Internal Strains

AbstractA modeling of nanoparticles and ab initio simulation of the scattered intensity from the Debye functions is used as a tool for an examination of the strain induced under high pressure in nanocrystalline silicon carbide and diamond. The analysis of the experimental intensity profiles includes a determination of the atomic structure and microstructure of the materials. The advantages of modeling over conventional methods of the analysis of powder diffraction data are discussed. Examples of using the modeling for determination of the shape and size and of one dimensional disordering in very small particles (2-4 nm), and development of internal strains in 10 nm SiC nanocrystals subjected to high pressures are given.

In-situ ultrasonic calibrations of pressure and temperature in a hinge-type double-stage cubic large volume press

2022 ◽  
Author(s):  
Qingze Li ◽  
Xiping Chen ◽  
Lei Xie ◽  
Tiexin Han ◽  
Jiacheng Sun ◽  
...  
Keyword(s):  
Travel Time ◽  
Large Volume ◽  
High Pressures ◽  
Physical Property ◽  
Calibration Method ◽  
Precise Determination ◽  
Thermal Cell ◽  
Acoustic Travel Time

Abstract Here, simultaneous in-situ calibration of pressures and temperatures was performed in a hinge-type second-stage cubic large volume press (LVP) up to 15 GPa and 1400 K by an acoustic travel-time approach. Based on the recently reported P-t S and P-T-t P -t S equations for Al2O3 buffer rod, the cell pressures and temperatures in the chamber of LVP were in-situ determined, in comparison with those by conventional off-line (or fixed-points) pressure calibration method and direct thermocouple measurement, respectively. It is found that the cell pressures of the LVP chamber are significantly reduced after annealing at simultaneous high pressures and high temperatures, owing to the stress relaxation as accumulate in the LVP chamber. This acoustic travel-time method is validated to be a good way for precise determination of thermal (cell) pressures at high temperature conditions, and is of great importance and necessity to conduct in-situ physical property measurements under extreme high P-T conditions, especially when the precious synchrotron X-ray/neutron diffraction beams are not available.

CORRELATION BETWEEN STRUCTURAL STABILITY AND ELECTRONIC STRUCTURE OF UGa3 UP TO 30 GPa

2011 ◽  
Vol 25 (04) ◽  
pp. 551-559 ◽  
Author(s):  
V. KATHIRVEL ◽  
SHARAT CHANDRA ◽  
N. V. CHANDRA SHEKAR ◽  
P. CH. SAHU ◽  
M. RAJAGOPALAN
Keyword(s):  
Structural Stability ◽  
High Pressures ◽  
Structural Phase ◽  
Maximum Pressure ◽  
Full Potential ◽  
X Ray Diffraction ◽  
Pressure Derivative ◽  
Augmented Plane Wave ◽  
Diamond Anvil ◽  
Structure Calculations

High-pressure angle-dispersive X-ray diffraction experiments were performed on UGa 3 up to 30 GPa within a diamond-anvil cell. UGa 3 remains in its cubic AuCu 3 type structure up to the maximum pressure studied and does not show any structural phase transition. To understand the structural stability of UGa 3, band structure calculations were performed as a function of reduced volume using the full-potential linear augmented plane wave (FP-LAPW) method. The results show that the Fermi level coincides with a deep valley in the density of states (DOS) curve in the antiferromagnetic state, whereas it lies near a valley (towards the bonding side) in the nonmagnetic state. At high pressures, the DOS near EF does not show much variation in both the cases. The experimental and theoretical equation of state, bulk modulus, and its pressure derivative values are also reported. The pressure dependence of magnetic moment shows a linear decrease at the rate of dμ/dP = -0.027 μ B / GPa .

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