scholarly journals Pressure-Temperature Phase Relations in Complex Hydrides

2009 ◽  
Vol 150 ◽  
pp. 175-195 ◽  
Author(s):  
Bertil Sundqvist
Keyword(s):  
High Pressure ◽  
Phase Diagrams ◽  
Structural Properties ◽  
High Pressures ◽  
Structural Phase ◽  
Experimental Studies ◽  
Strong Increase ◽  
Temperature Phase ◽  
Complex Hydrides ◽  
Theoretical Predictions

Interest in hydrogen as a future energy carrier in mobile applications has led to a strong increase in research on the structural properties of complex alkali metal and alkaline earth hydrides, with the aim to find structural phases with higher hydrogen densities. This contribution reviews recent work on the structural properties and phase diagrams of these complex hydrides under elevated pressures, an area where rapid progress has been made over the last few years. The materials discussed in greatest detail are LiAlH4, NaAlH4, Li3AlH6, Na3AlH6, LiBH4, NaBH4, and KBH4. All of these have been studied under high pressure by various methods such as X-ray or neutron scattering, Raman spectroscopy, differential thermal analysis or thermal conductivity measurements in order to find information on their structural phase diagrams. Based mainly on experimental studies, preliminary or partial phase diagrams are also given for six of these materials. In addition to this information, data are provided also on experimental results for a number of other complex hydrides, and theoretical predictions of new phases and structures under high pressures are reviewed for several materials not yet studied experimentally under high pressure.

Synchrotron Moessbauer Spectroscopy and Resistivity Studies of Iron Oxide Under High Pressure

2006 ◽  
Vol 987 ◽  
Author(s):  
Viktor V. Struzhkin ◽  
Mikhail I. Eremets ◽  
Ivan M. Eremets ◽  
Jung-Fu Lin ◽  
Wolfgang Sturhahn ◽  
...  
Keyword(s):  
High Pressure ◽  
Magnetic Properties ◽  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
High Pressures ◽  
Structural Phase ◽  
Experimental Studies ◽  
Magnetic Interactions ◽  
Diamond Anvil

AbstractThe strong electron correlations play a crucial role in the formation of a variety of electronic and magnetic properties of the transition metal oxides. In strongly correlated electronic materials many theoretical predictions exist on pressure-induced insulator-metal transitions, which are followed by a collapse of localized magnetic moments and by structural phase transitions [1]. The high-pressure studies provide additional degree of freedom to control the structural, electronic, optical, and magnetic properties of transition metal oxides. With the development of the high-pressure diamond-anvil-cell technique the experimental studies of such transitions are now possible with the advanced synchrotron techniques. In our studies, the iron monooxide Fe0.94O was studied under high pressures up to 200 GPa in diamond anvil cells. The single crystals enriched with Fe57 isotopes have been prepared for nuclear resonance measurements. The results of synchrotron Mössbauer spectroscopy (nuclear forward scattering -NFS), and electro-resistivity measurements suggest a complicated scenario of magnetic interactions governed by band-broadening effects.

High-pressure structural phase transition and metallization in Ga2S3 under non-hydrostatic and hydrostatic conditions up to 36.4 GPa

2021 ◽  
Author(s):  
Linfei Yang ◽  
Jianjun Jiang ◽  
Lidong Dai ◽  
Haiying Hu ◽  
Meiling Hong ◽  
...  
Keyword(s):  
Phase Transition ◽  
Raman Spectroscopy ◽  
High Pressure ◽  
Structural Properties ◽  
Structural Phase Transition ◽  
First Principles ◽  
Theoretical Calculations ◽  
Structural Phase

The vibrational, electrical and structural properties of Ga2S3 were explored by Raman spectroscopy, EC measurements, HRTEM and First-principles theoretical calculations under different pressure environments up to 36.4 GPa.

PRESSURE-INDUCED ELECTRONIC PHASE TRANSITIONS AND SUPERCONDUCTIVITY IN TITANIUM

2009 ◽  
Vol 23 (05) ◽  
pp. 723-741 ◽  
Author(s):  
K. IYAKUTTI ◽  
C. NIRMALA LOUIS ◽  
S. ANURATHA ◽  
S. MAHALAKSHMI
Keyword(s):  
High Pressure ◽  
Band Structure ◽  
Fermi Surface ◽  
High Pressures ◽  
Ambient Pressure ◽  
Structural Phase ◽  
Normal Pressure ◽  
Orbital Method ◽  
Superconducting Transition ◽  
Electronic Band

The electronic band structure, density of states, structural phase transition, superconducting transition and Fermi surface cross section of titanium ( Ti ) under normal and high pressures are reported. The high pressure band structure exhibits significant deviations from the normal pressure band structure due to s → d transition. On the basis of band structure and total energy results obtained using tight-binding linear muffin-tin orbital method (TB LMTO), we predict a phase transformation sequence of α( hcp ) → ω (hexagonal) → γ (distorted hcp) → β (bcc) in titanium under pressure. From our analysis, we predict a δ (distorted bcc) phase which is not stable at any high pressures. At ambient pressure, the superconducting transition occurs at 0.354 K. When the pressure is increased, it is predicted that, Tc increases at a rate of 3.123 K/Mbar in hcp–Ti . On further increase of pressure, Tc begins to decrease at a rate of 1.464 K/Mbar. The highest value of Tc(P) estimated is 5.043 K for hcp–Ti , 4.538 K for ω– Ti and 4.85 K for bcc – Ti . From this, it is inferred that the maximum value of Tc(P) is rather insensitive to the crystal structure of Ti . The nonlinearities in Tc(P) is explained by considering the destruction and creation of new parts of Fermi surface at high pressure. At normal pressure, the hardness of Ti is in the following order: ω- Ti > hcp - Ti > bcc- Ti > γ- Ti .

Formation of two crystal modifications of Fe7C3−x at 5.5 GPa

2019 ◽  
Vol 52 (6) ◽  
pp. 1378-1384
Author(s):  
Sergey Gromilov ◽  
Anatoly Chepurov ◽  
Valeri Sonin ◽  
Egor Zhimulev ◽  
Aleksandr Sukhikh ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Experimental Studies ◽  
X Ray Diffraction ◽  
High Iron Content ◽  
X Ray ◽  
High Pressure High Temperature ◽  
Micro Analysis ◽  
Crystal Modifications ◽  
High Pressure Apparatus

The Fe–C system, which is widely used to grow commercial high-pressure–high-temperature diamond monocrystals, is rather complicated due to the formation of carbides. The carbide Fe3C is a normal run product, but the pressure at which Fe7C3 carbide becomes stable is a subject of discussion. This paper demonstrates the synthesis of Fe7C3 carbide and its detailed study using single-crystal and powder X-ray diffraction, as well as electron probe micro-analysis and scanning electron microscopy. The experiments were performed using a multiple-anvil high-pressure apparatus of `split-sphere' (BARS) type at a pressure of 5.5 GPa and a temperature of 1623 K. Our results show that in the Fe–C system, in addition to diamond, a phase that corresponds to the Fe7C3 carbide was synthesized. This means that both carbides (Fe7C3 and Fe3C) are stable at 5.5 GPa. Two crystal phases are described, Fe14C6 and Fe28C12−x . Fe14C6 is based on the well known rhombic structure of Fe7C3, while Fe28C12−x has a different packing order of Fe6C polyhedrons. The results obtained in this study should be taken into account when synthesizing and growing diamond at high pressures and temperatures in metal–carbon systems with a high iron content, as well as when conducting experimental studies on the synthesis of diamond directly from carbide.

Advances in Computation of Temperature-Pressure Phase Diagrams of High-Pressure Nitrides

2008 ◽  
Vol 403 ◽  
pp. 77-80 ◽  
Author(s):  
Peter Kroll
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Elevated Temperature ◽  
Total Energy ◽  
Phase Diagrams ◽  
High Pressures ◽  
First Principle ◽  
Energy Calculations ◽  
High Pressure High Temperature ◽  
Pressure Phase

A combination of first-principle and thermochemical calculations is applied to compute the phase diagrams of rhenium-nitrogen and of ruthenium-nitrogen at elevated temperature and high pressure. We augment total energy calculations with our approach to treat the nitrogen fugacity at high pressures. We predict a sequential nitridation of Re at high-pressure/high-temperature conditions. At 3000 K, ReN will form from Re and nitrogen at about 32 GPa. A ReN2 with CoSb2-type structure may be achieved at pressures exceeding 50 GPa at this temperature. Marcasite-type RuN2 will be attainable at 3000 K at pressures above 30 GPa by reacting Ru with nitrogen.

Design and Analysis of a High Pressure Apparatus

1980 ◽  
Vol 102 (3) ◽  
pp. 633-640
Author(s):  
K. C. Rolle ◽  
J. N. Crisp ◽  
A. N. Palazotto
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
Phase Diagrams ◽  
High Pressures ◽  
Equilibrium Phase ◽  
Original Design ◽  
Piston Displacement ◽  
Crude Analysis ◽  
High Pressure Apparatus

In the determination of equilibrium phase diagrams, i.e., pressure volume-temperature relations for lubricants at pressures up to 2800 MPa and temperatures of 378K, one must carry out a highly sophisticated design of a high pressure apparatus. In 1935 Bridgman designed a piston-displacement device and measured the compressibility of numerous materials at high pressures. However, in order to obtain accurate equilibrium phase diagrams for lubricants, Bridgman’s relatively crude analysis must be considerably refined. The authors have extended this original design using finite element techniques to accurately correct pertinent measurements which are in turn incorporated into the expressions used in determining the pressure-volume temperature relations of lubricants.

scholarly journals Study on the High-Pressure Behavior of Goethite up to 32 GPa Using X-Ray Diffraction, Raman, and Electrical Impedance Spectroscopy

Minerals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 99 ◽  
Author(s):  
Ruilian Tang ◽  
Jiuhua Chen ◽  
Qiaoshi Zeng ◽  
Yan Li ◽  
Xue Liang ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Impedance Spectroscopy ◽  
Electrical Impedance ◽  
High Pressures ◽  
Structural Phase ◽  
Second Order ◽  
Electrical Impedance Spectroscopy ◽  
X Ray Diffraction ◽  
X Ray

Goethite is a major iron-bearing sedimentary mineral on Earth. In this study, we conducted in situ high-pressure x-ray diffraction, Raman, and electrical impedance spectroscopy measurements of goethite using a diamond anvil cell (DAC) at room temperature and high pressures up to 32 GPa. We observed feature changes in both the Raman spectra and electrical resistance at about 5 and 11 GPa. However, the x-ray diffraction patterns show no structural phase transition in the entire pressure range of the study. The derived pressure-volume (P-V) data show a smooth compression curve with no clear evidence of any second-order phase transition. Fitting the volumetric data to the second-order Birch–Murnaghan equation of state yields V0 = 138.9 ± 0.5 Å3 and K0 = 126 ± 5 GPa.

scholarly journals A phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds

2018 ◽  
Vol 5 (6) ◽  
pp. 180058 ◽  
Author(s):  
Michel Couzi ◽  
François Guillaume ◽  
Kenneth D. M. Harris
Keyword(s):  
Structural Properties ◽  
Phenomenological Model ◽  
Inclusion Compounds ◽  
Structural Phase ◽  
Temperature Phase ◽  
Coupling Mechanism ◽  
Repeat Distance ◽  
Guest Molecules ◽  
Urea Inclusion Compounds ◽  
Urea Inclusion

n -Alkane/urea inclusion compounds are crystalline materials in which n -alkane ‘guest’ molecules are located within parallel one-dimensional ‘host’ tunnels formed by a helical hydrogen-bonded arrangement of urea molecules. The periodic repeat distance of the guest molecules along the host tunnels is incommensurate with the periodic repeat distance of the host substructure. The structural properties of the high-temperature phase of these materials (phase I), which exist at ambient temperature, are described by a (3 + 1)-dimensional superspace. Recent publications have suggested that, in the prototypical incommensurate composite systems, n -nonadecane/urea and n -hexadecane/urea, two low-temperature phases II and ‘III’ exist and that one or both of these phases are described by a (3 + 2)-dimensional superspace. We present a phenomenological model based on symmetry considerations and developed in the frame of a pseudo-spin–phonon coupling mechanism, which accounts for the mechanisms responsible for the I ↔ II ↔ ‘III’ phase sequence. With reference to published experimental data, we demonstrate that, in all phases of these incommensurate materials, the structural properties are described by (3 + 1)-dimensional superspace groups. Around the temperature of the II ↔ ‘III’ transition, the macroscopic properties of the material are not actually associated with a phase transition, but instead represent a ‘crossover’ between two regimes involving different couplings between relevant order parameters.

scholarly journals High-pressure diffraction studies of molecular organic solids. A personal view

2007 ◽  
Vol 64 (1) ◽  
pp. 218-231 ◽  
Author(s):  
Elena V. Boldyreva
Keyword(s):  
High Pressure ◽  
Solid State ◽  
High Pressures ◽  
Experimental Studies ◽  
Personal View ◽  
Organic Solids ◽  
High Pressure Studies

This paper discusses the trends in the experimental studies of molecular organic solids at high pressures by diffraction techniques. Crystallization of liquids, crystallization from solutions and solid-state transformations are considered. Special attention is paid to the high-pressure studies of pharmaceuticals and of biomimetics.

Structural stability of WS2 under high pressure

2014 ◽  
Vol 28 (25) ◽  
pp. 1450168 ◽  
Author(s):  
Nirup Bandaru ◽  
Ravhi S. Kumar ◽  
Jason Baker ◽  
Oliver Tschauner ◽  
Thomas Hartmann ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
High Temperature ◽  
Structural Changes ◽  
High Pressures ◽  
Structural Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diamond Anvil ◽  
Heating Up

Structural behavior of bulk WS 2 under high pressure was investigated using synchrotron X-ray diffraction and diamond anvil cell up to 52 GPa along with high temperature X-ray diffraction and high pressure Raman spectroscopy analysis. The high pressure results obtained from X-ray diffraction and Raman analysis did not show any pressure induced structural phase transformations up to 52 GPa. The high temperature results show that the WS 2 crystal structure is stable upon heating up to 600°C. Furthermore, the powder X-ray diffraction obtained on shock subjected WS 2 to high pressures up to 10 GPa also did not reveal any structural changes. Our results suggest that even though WS 2 is less compressible than the isostructural MoS 2, its crystal structure is stable under static and dynamic compressions up to the experimental limit.

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