Search results for "Pressure range"
showing 10 items of 23 documents
Thallium under extreme compression
2016
We present a combined theoretical and experimental study of the high-pressure behavior of thallium. X-ray diffraction experiments have been carried out at room temperature up to 125 GPa using diamond-anvil cells, nearly doubling the pressure range of previous experiments. We have confirmed the hcp-fcc transition at 3.5 GPa and determined that the fcc structure remains stable up to the highest pressure attained in the experiments. In addition, HP-HT experiments have been performed up to 8 GPa and 700 K by using a combination of x-ray diffraction and a resistively heated diamond-anvil cell. Information on the phase boundaries is obtained, as well as crystallographic information on the HT bcc …
A study of KNbO3in the pressure range to 12 GPa using synchrotron radiation
1997
Abstract Orthorhombic KNbO3 has been studied by x-ray diffraction as a function of pressure. The lattice cell parameters, volume and stability range of this phase have been determined as a function of the applied pressure. No structural transformation has been observed up to 12 GPa. The resulting P-V data are fitted to a Murnaghan equation state of first-order.
High-pressure structural investigation of several zircon-type orthovanadates
2009
Room temperature angle-dispersive x-ray diffraction measurements on zircon-type EuVO4, LuVO4, and ScVO4 were performed up to 27 GPa. In the three compounds we found evidence of a pressure-induced structural phase transformation from zircon to a scheelite-type structure. The onset of the transition is near 8 GPa, but the transition is sluggish and the low- and high-pressure phases coexist in a pressure range of about 10 GPa. In EuVO4 and LuVO4 a second transition to a M-fergusonite-type phase was found near 21 GPa. The equations of state for the zircon and scheelite phases are also determined. Among the three studied compounds, we found that ScVO4 is less compressible than EuVO4 and LuVO4, b…
New high-pressure phase of HfTiO4 and ZrTiO4 ceramics
2010
We studied the high-pressure effects on the crystalline structure of monoclinic HfTiO4 and ZrTiO4. We found that the compressibility of these ceramics is highly non-isotropic, being the b-axis the most compressible one. In addition, the a-axis is found to have a small and negative compressibility. At 2.7 GPa (10.7 GPa) we discovered the onset of an structural phase transition in HfTiO4 (ZrTiO4), coexisting the low- and high-pressure phases in a broad pressure range. The new high-pressure phase has a monoclinic structure which involves an increase in the Ti-O coordination and a collapse of the cell volume. The equation of state for the low-pressure phase is also determined.
Selective adsorption of formaldehyde and water vapors in NaY and NaX zeolites
2019
International audience; Coadsorption of formaldehyde and water vapors on NaX and NaY zeolites is studied at 298 K in the pressure range 0-2 hPa by manometry coupled with gas phase chromatography and calorimetry. Coadsorption isotherms, adsorption selectivities and coadsorption heats are measured. Results show that the coadsorption process is selective for water at low filling and for formaldehyde at high filling. The adsorption selectivity for formaldehyde over water is however too low to consider the possibility of using such adsorbents for the development of air handling units. On the other hand, a preliminary study carried out on the adsorption of formaldehyde and water in pure gas phase…
Novel structural phases and the properties of LaX (X = P, As) under high pressure: first-principles study
2020
The particle swarm optimization algorithm and density functional theory (DFT) are extensively performed to determine the structures, phase transition, mechanical stability, electronic structures, and thermodynamic properties of lanthanide phosphates (LaP and LaAs) in the pressure range of 0 to 100 GPa. Two novel high-pressure structures of LaP and LaAs are first reported here. It is found that LaX (X = P, As) undergo a phase transition from NaCl-type structure (Fm3m) to CsCl-type structure (P4/mmm) at 19.04 GPa and 17.22 GPa, respectively. With the elevation of the pressure, C2/m-LaP and Imma-LaAs are the most stable structures up to 70.08 GPa and 85.53 GPa, respectively. Finally, the analy…
Aluminium distribution in an Earth's non–primitive lower mantle
2020
The aluminium incorporation mechanism of perovskite was explored by means of quantum mechanics in combination with equilibrium/off-equilibrium thermodynamics under the pressure-temperature conditions of the Earth's lower mantle (from 24 to 80 GPa). Earth's lower mantle was modelled as a geochemically non-primitive object because of an enrichment by 3 wt% of recycled crustal material (MORB component). The compositional modelling takes into account both chondrite and pyrolite reference models. The capacity of perovskite to host Al was modelled through an Al2O3 exchange process in an unconstrained Mg-perovskite + Mg-Al-perovskite + free-Al2O3(corundum) system. Aluminium is globally incorporate…
Lattice phonon modes of the high-pressure phase CuCl-IV
1999
Raman spectra of isotopically pure CuCl samples ${(}^{63}\mathrm{CuCl}$ and ${}^{65}\mathrm{CuCl})$ were measured under hydrostatic pressure up to 14 GPa at low temperature $(5 \mathrm{K}).$ Up to six Raman modes were resolved for the binary BC8-analog phase CuCl-IV in the range from 4.1 to 14 GPa. The phonon dispersion relations of this phase were calculated within a rigid ion model. Based on this calculation an assignment for the observed Raman-active modes is proposed. The calculated pressure dependences of mode frequencies reproduce the experimental results. Raman spectra support the existence of the phase CuCl-IIa in a narrow pressure range from 3.3 to 4.1 GPa.
First-principles LCAO study of the low and room temperature phases of CdPS$_3$
2020
A.K. is grateful to the Latvian Council of Science project no. lzp-2018/2-0353 for financial support. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.
High Pressure Raman, Optical Absorption, and Resistivity Study of SrCrO4
2018
We studied the electronic and vibrational properties of monazite-type SrCrO4 under compression. The study extended the pressure range of previous studies from 26 to 58 GPa. The existence of two previously reported phase transitions was confirmed at 9 and 14 GPa, and two new phase transitions were found at 35 and 48 GPa. These transitions involve several changes in the vibrational and transport properties with the new high-pressure phases having a conductivity lower than that of the previously known phases. No evidence of chemical decomposition or metallization of SrCrO4 was detected. A tentative explanation for the reported observations is discussed.