Electronic, Magnetic and Structural Properties of the RFeO3 Antiferromagnetic-Perovskites at Very High Pressures

2002 ◽  
Vol 718 ◽  
Author(s):  
Moshe P. Pasternak ◽  
W. M. Xu ◽  
G. Kh. Rozenberg ◽  
R. D. Taylor
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Ambient Pressure ◽  
Magnetic Ordering ◽  
Exchange Interactions ◽  
Volume Reduction ◽  
Metallic State ◽  
First Order Phase Transition ◽  
Diamond Anvil ◽  
First Order Phase

AbstractAt ambient pressure the orthorhombic perovskites R-orthoferrites (R Ξ Lu, Eu, Y, Pr, and La) exhibit very large optical gaps. These large- gap Mott insulators in which the 3d5 high-spin ferric ions carry large local moments and magnetically order at TN > 600 K, undergo a sluggish structural first-order phase transition in the 30-50 GPa range, with the exception of the LuFeO3 which undergoes an isostructural volume reduction resulting from a high to low-spin crossover. High-pressure methods to 170 GPa using Mossbauer spectroscopy, resistance, and synchrotronbased XRD in diamond anvil cells were applied. Following the quasi-isostructural volume reduction (3-5%) the new phase the magnetic-ordering temperature is drastically reduced, to ∼ 100 K, the direct and super-exchange interactions are drastically weakened, and the charge-transfer gap is substantially reduced. The high-pressure (HP) phases of the La and Pr oxides, at their inception, are composed of high- and low-spin Fe3+ magnetic sublattices, the abundance of the latter increasing with pressure but HP phases of the Eu, Y, and Lu oxides consist solely of low-spin Fe3+. Resistance and Mössbauer studies in La and Pr orthoferrites reveal the onset of a metallic state with moments starting at P > 120 GPa. Based on the magnetic and electrical data of the latter species, a Mott phase diagram was established.

High-pressure transformations of NbO2F

2000 ◽  
Vol 56 (2) ◽  
pp. 189-196 ◽  
Author(s):  
Stefan Carlson ◽  
Ann-Kristin Larsson ◽  
Franziska E. Rohrer
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
High Pressures ◽  
Ambient Pressure ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
Rietveld Refinements ◽  
X Ray ◽  
Anion Coordination ◽  
Diamond Anvil

The ReO3-type structure NbO2F, niobium dioxyfluoride, has been studied at high pressures using diamond anvil cells and synchrotron X-ray radiation. High-pressure powder diffraction measurements have been performed up to 40.1 GPa. A phase transition from the cubic (Pm3¯m) ambient pressure structure to a rhombohedral (R3¯c) structure at 0.47 GPa has been observed. Rietveld refinements at 1.38, 1.96, 3.20, 6.23, 9.00 and 10.5 GPa showed that the transition involves an a − a − a − tilting of the cation–anion coordination octahedra and a change of the anion–anion arrangement to approach hexagonal close packing. Compression and distortion of the Nb(O/F)6 octahedra is also revealed by the Rietveld refinements. At 17–18 GPa, the diffraction pattern disappears and the structure becomes X-ray amorphous.

Structural phase transition of CeAuGe at high pressure

2005 ◽  
Vol 220 (2/3) ◽  
Author(s):  
Valeri Brouskov ◽  
Michael Hanfland ◽  
Rainer Pöttgen ◽  
Ulrich Schwarz
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Structural Phase ◽  
Lattice Parameter ◽  
First Order ◽  
First Order Phase Transition ◽  
Diamond Anvil ◽  
Ternary Intermetallic Compound ◽  
First Order Phase ◽  
Type Crystal

AbstractStructural properties of the ternary intermetallic compound CeAuGe were investigated at hydrostatic pressures up to 15 GPa with high-resolution angle dispersive X-ray powder diffraction using synchrotron radiation and the diamond anvil cell technique. At 8.7(7) GPa a first order phase transition is observed from a hexagonal NdPtSb-type arrangement into an orthorhombic high-pressure modification with a TiNiSi-type crystal structure. The transformation is associated with a 3% shortening of the lattice parameter perpendicular to the puckered layers [AuGe]

scholarly journals Crystal structure of the high-pressure phase of the oxonitridosilicate chloride Ce4[Si4O3 + x N7 − x ]Cl1 − x O x , x ≃ 0.2

2006 ◽  
Vol 62 (2) ◽  
pp. 205-211 ◽  
Author(s):  
Alexandra Friedrich ◽  
Eiken Haussühl ◽  
Wolfgang Morgenroth ◽  
Alexandra Lieb ◽  
Björn Winkler ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Single Crystal ◽  
Structural Changes ◽  
Low Pressure ◽  
First Order Phase Transition ◽  
Compression Mechanism ◽  
Diamond Anvil ◽  
Structural Mechanisms ◽  
First Order Phase

The structural compression mechanism of Ce4[Si4O3 + x N7 − x ]Cl1 − x O x , x ≃ 0.2, was investigated by in situ single-crystal synchrotron X-ray diffraction at pressures of 3.0, 8.5 and 8.6 GPa using the diamond–anvil cell technique. On increasing pressure the low-pressure cubic structure first undergoes only minor structural changes. Between 8.5 and 8.6 GPa a first-order phase transition occurs, accompanied by a change of the single-crystal colour from light orange to dark red. The main structural mechanisms, leading to a volume reduction of about 5% at the phase transition, are an increase in and a rearrangement of the Ce coordination, the loss of the Ce2, Ce3 split position, and a bending of some of the inter-polyhedral Si—N—Si angles in the arrangement of the corner-sharing Si tetrahedra. The latter is responsible for the short c axis of the orthorhombic high-pressure structure compared with the cell parameter of the cubic low-pressure structure.

High Pressure Solid State Chemistry of A3(VO4)2 Compounds (A: Ca, Sr, Ba)

1997 ◽  
Vol 499 ◽  
Author(s):  
Andrzej Grzechnik ◽  
Paul F. McMillan
Keyword(s):  
High Pressure ◽  
Ambient Pressure ◽  
Close Packing ◽  
Solid State Chemistry ◽  
Fold Axis ◽  
X Ray Diffraction ◽  
First Order Phase Transition ◽  
Olivine Structure ◽  
First Order Phase

ABSTRACTThe purpose of this study is to explore the potential of high pressure methods for preparation of new series of compounds in the A3(VO4)2 systems (A: Ca, Sr, Ba). In this study, we present our in situ vibrational and X-ray diffraction data on the behavior of the A3(VO4)2 compounds at high pressure and room temperature. Upon compression up to 290 kbar, there is no phase change in Ba3(VO4)2. Sr3(VO4)2 undergoes a first order phase transition to an olivine-like structure at about 150 kbar. In both the ambient pressure and olivine structures of Sr3(VO4)2, oxygen atoms form a hexagonal close packing. The packing in the olivine structure is distorted from this due to loss of 3-fold axis. Ca3(VO4)2 amorphizes at about 100 kbar. The high pressure behavior of the compounds studied here is related to the size of the A(2)2+ cations. Small Ca(2)2+ cations hinder the completion of crystal-to-crystal transformations in Ca3(VO4)2.

scholarly journals The thermal conductivity of the Earth's core and implications for its thermal and compositional evolution

2020 ◽  
Author(s):  
Kenji Ohta ◽  
Kei Hirose
Keyword(s):  
Thermal Conductivity ◽  
High Pressure ◽  
Thermal History ◽  
Diamond Anvil Cell ◽  
High Pressures ◽  
Iron Alloys ◽  
Compositional Evolution ◽  
The Earth ◽  
Diamond Anvil ◽  
High Pressures And Temperatures

Abstract Precise determinations of the thermal conductivity of iron alloys at high pressures and temperatures are essential for understanding the thermal history and dynamics of the metallic cores of the Earth. We review relevant high-pressure experiments using a diamond-anvil cell and discuss implications of high core conductivity for its thermal and compositional evolution.

scholarly journals Liquid–liquid phase transition in hydrogen by coupled electron–ion Monte Carlo simulations

2016 ◽  
Vol 113 (18) ◽  
pp. 4953-4957 ◽  
Author(s):  
Carlo Pierleoni ◽  
Miguel A. Morales ◽  
Giovanni Rillo ◽  
Markus Holzmann ◽  
David M. Ceperley
Keyword(s):  
Phase Transition ◽  
Monte Carlo ◽  
Density Functional ◽  
Fluid Phase ◽  
Transition Line ◽  
Energy Applications ◽  
First Order Phase Transition ◽  
Fundamental Research ◽  
Diamond Anvil ◽  
First Order Phase

The phase diagram of high-pressure hydrogen is of great interest for fundamental research, planetary physics, and energy applications. A first-order phase transition in the fluid phase between a molecular insulating fluid and a monoatomic metallic fluid has been predicted. The existence and precise location of the transition line is relevant for planetary models. Recent experiments reported contrasting results about the location of the transition. Theoretical results based on density functional theory are also very scattered. We report highly accurate coupled electron–ion Monte Carlo calculations of this transition, finding results that lie between the two experimental predictions, close to that measured in diamond anvil cell experiments but at 25–30 GPa higher pressure. The transition along an isotherm is signaled by a discontinuity in the specific volume, a sudden dissociation of the molecules, a jump in electrical conductivity, and loss of electron localization.

scholarly journals Pressure-Dependent Clustering in Ionic-Liquid-Poly (Vinylidene Fluoride) Mixtures: An Infrared Spectroscopic Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 2099
Author(s):  
Teng-Hui Wang ◽  
Wei-Xiang Wang ◽  
Hai-Chou Chang
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Vinylidene Fluoride ◽  
Ambient Pressure ◽  
Infrared Spectroscopic Study ◽  
Research Attention ◽  
Nanoscale Structures ◽  
Local Structures ◽  
Poly Vinylidene Fluoride ◽  
Hydrogen Bonded

The nanostructures of ionic liquids (ILs) have been the focus of considerable research attention in recent years. Nevertheless, the nanoscale structures of ILs in the presence of polymers have not been described in detail at present. In this study, nanostructures of ILs disturbed by poly(vinylidene fluoride) (PVdF) were investigated via high-pressure infrared spectra. For 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HEMIm][TFSI])-PVdF mixtures, non-monotonic frequency shifts of the C4,5-H vibrations upon dilution were observed under ambient pressure. The experimental results suggest the presence of microheterogeneity in the [HEMIm][TFSI] systems. Upon compression, PVdF further influenced the local structure of C4,5–H via pressure-enhanced IL–PVdF interactions; however, the local structures of C2–H and hydrogen-bonded O–H were not affected by PVdF under high pressures. For choline [TFSI]–PVdF mixtures, PVdF may disturb the local structures of hydrogen-bonded O–H. In the absence of the C4,5–H⋯anion and C2–H⋯anion in choline [TFSI]–PVdF mixtures, the O–H group becomes a favorable moiety for pressure-enhanced IL–PVdF interactions. Our results indicate the potential of high-pressure application for designing pressure-dependent electronic switches based on the possible changes in the microheterogeneity and electrical conductivity in IL-PVdF systems under various pressures.

scholarly journals Lab in a DAC – high-pressure crystal chemistry in a diamond-anvil cell

2019 ◽  
Vol 75 (6) ◽  
pp. 918-926 ◽  
Author(s):  
Andrzej Katrusiak
Keyword(s):  
High Pressure ◽  
Diamond Anvil Cell ◽  
Ambient Pressure ◽  
Elevated Pressure ◽  
Sample Volume ◽  
Chemical Research ◽  
New Era ◽  
New Information ◽  
Intermolecular Contacts ◽  
Diamond Anvil

The diamond-anvil cell (DAC) was invented 60 years ago, ushering in a new era for material sciences, extending research into the dimension of pressure. Most structural determinations and chemical research have been conducted at ambient pressure, i.e. the atmospheric pressure on Earth. However, modern experimental techniques are capable of generating pressure and temperature higher than those at the centre of Earth. Such extreme conditions can be used for obtaining unprecedented chemical compounds, but, most importantly, all fundamental phenomena can be viewed and understood from a broader perspective. This knowledge, in turn, is necessary for designing new generations of materials and applications, for example in the pharmaceutical industry or for obtaining super-hard materials. The high-pressure chambers in the DAC are already used for a considerable variety of experiments, such as chemical reactions, crystallizations, measurements of electric, dielectric and magnetic properties, transformations of biological materials as well as experiments on living tissue. Undoubtedly, more applications involving elevated pressure will follow. High-pressure methods become increasingly attractive, because they can reduce the sample volume and compress the intermolecular contacts to values unattainable by other methods, many times stronger than at low temperature. The compressed materials reveal new information about intermolecular interactions and new phases of single- and multi-component compounds can be obtained. At the same time, high-pressure techniques, and particularly those of X-ray diffraction using the DAC, have been considerably improved and many innovative developments implemented. Increasingly more equipment of in-house laboratories, as well as the instrumentation of beamlines at synchrotrons and thermal neutron sources are dedicated to high-pressure research.

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 .

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