High Pressure Carbon Behavior Induced from Carbide Hugoniots

1997 ◽  
Vol 499 ◽  
Author(s):  
T. Sekine ◽  
E. Takazawa ◽  
T. Kobayashi
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
Molar Volume ◽  
Partial Molar Volume ◽  
High Pressures ◽  
Diamond Structure ◽  
Structural Variations ◽  
Diamond Phase ◽  
Type Carbide ◽  
Diamond Type

ABSTRACTInvestigations of Hugoniots the diamond-type carbides(various SiC) and NaCl-type carbides such as TiC give some insights into the high-pressure carbon behaviors. The experimental results of phase transitions of a-SiC and β-SiC, together with those of diamond-structure Si, imply that the candidate as post-diamond phase has sixfold coordination and that a possible transition pressure is about 1–2 TPa. The NaCl-type carbide Hugoniots indicate that sixfold coordinated C is very stable at high pressures. The partial molar volume of carbon in the NaCl-type carbides ranges between 1.4 to 2.6 cnvVg-atom C at 1 atm and reaches about 2.8 cm3/g-atom C at 100 GPa. Taking into account structural variations of the corresponding metals, the volume of the sixfold coordinated C is estimated to be 1.7 cm3/g-atom C, about half of that of diamond, and the post-diamond phase appears to be extremely hard.

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

Phase transitions of BaCO3 at high pressures

2008 ◽  
Vol 72 (2) ◽  
pp. 659-665 ◽  
Author(s):  
S. Ono ◽  
J. P. Brodholt ◽  
G. D. Price
Keyword(s):  
Phase Transition ◽  
Experimental Study ◽  
High Pressure ◽  
Phase Transitions ◽  
Bulk Modulus ◽  
First Principles ◽  
High Pressures ◽  
Ambient Conditions ◽  
The Stability ◽  
Previous Experimental Study

AbstractFirst-principles simulations and high-pressure experiments were used to study the stability of BaCO3 carbonates at high pressures. Witherite, which is orthorhombic and isotypic with CaCO3 aragonite, is stable at ambient conditions. As pressure increases, BaCO3 transforms from witherite to an orthorhombic post-aragonite structure at 8 GPa. The calculated bulk modulus of the post-aragonite structure is 60.7 GPa, which is slightly less than that from experiments. This structure shows an axial anisotropicc ompressibility and the a axis intersects with the c axis at 70 GPa, which implies that the pressure-induced phase transition reported in previous experimental study is misidentified. Although a pyroxene-like structure is stable in Mg- and Ca-carbonates at pressures >100 GPa, our simulations showed that this structure does not appear in BaCO3.

ULTRASONIC PROPAGATION IN SOLENHOFEN LIMESTONE AT HIGH PRESSURES

Geophysics ◽  
1978 ◽  
Vol 43 (5) ◽  
pp. 1014-1017
Author(s):  
I. J. Fritz
Keyword(s):  
High Pressure ◽  
Wave Propagation ◽  
Phase Transitions ◽  
Seismic Waves ◽  
High Pressures ◽  
Sound Propagation ◽  
Wave Measurements ◽  
Ultrasonic Propagation ◽  
Propagation Properties ◽  
The Relationship

The measurement of ultrasonic velocities at high pressure in minerals and rocks provides information pertinent to a variety of geophysical and engineering problems such as those of determining the state of matter in the earth's interior, understanding the propagation of seismic waves, and characterizing mechanical behavior of materials that are important in mining technology. In recent years there have been a number of reported high pressure sound velocity measurements in various kinds of limestone. (A concise review of this work can be found in a recent paper by Singh and Kennedy, 1974.) Such measurements continue to be of interest because of the relationship to shock‐wave propagation properties (Grady et al, 1977). From the previous measurements it has been found that the phase transitions in calcite, which is the main constituent of limestone, strongly influence the sound velocities. The phase transitions in pure calcite occur at 14.5 kbar (calcite I–II) and 17.4 kbar (calcite II–III) (Singh and Kennedy, 1974); however, because the transitions may be shifted in pressure and spread out over a range of pressures in a rock, it is necessary to make measurements to pressures in excess of 20 kbar in order to characterize the effects of the transitions. To date there has been only one experimental study of the effect of the II–III transition on sound propagation, namely the longitudinal wave measurements in Oak Hall limestone made by Wang and Meltzer (1973). In order to further characterize the effect of the II–III transition on sound propagation in limestone, we have made measurements to 25 kbar on Solenhofen limestone. We were able to measure both longitudinal and transverse velocities over the full pressure range; thus, our measurements represent the first study of the effect of the II–III transition on shear wave propagation under conditions of hydro static pressure.

scholarly journals X-Ray Diffraction and Electron Microscopy Studies of the Size Effects on Pressure-Induced Phase Transitions in CdS Nanocrystals

MRS Advances ◽  
2020 ◽  
pp. 1-9
Author(s):  
Lingyao Meng ◽  
Hongyou Fan ◽  
J. Matthew Lane ◽  
Luke Baca ◽  
Jackie Tafoya ◽  
...  
Keyword(s):  
Phase Transition ◽  
Particle Size ◽  
High Pressure ◽  
Phase Transitions ◽  
Size Effects ◽  
High Pressures ◽  
Bulk Material ◽  
Cds Nanoparticles ◽  
X Ray ◽  
Potential Applications

Abstract In recent years, investigations of the phase transition behavior of semiconducting nanoparticles under high pressure has attracted increasing attention due to their potential applications in sensors, electronics, and optics. However, current understanding of how the size of nanoparticles influences this pressure-dependent property is somewhat lacking. In particular, phase behaviors of semiconducting CdS nanoparticles under high pressure have not been extensively reported. Therefore, in this work, CdS nanoparticles of different sizes are used as a model system to investigate particle size effects on high-pressure-induced phase transition behaviors. In particular, 7.5, 10.6, and 39.7 nm spherical CdS nanoparticles are synthesized and subjected to controlled high pressures up to 15 GPa in a diamond anvil cell. Analysis of all three nanoparticles using in-situ synchrotron wide-angle X-ray scattering (WAXS) data shows that phase transitions from wurtzite to rocksalt occur at higher pressures than for bulk material. Bulk modulus calculations not only show that the wurtzite CdS nanomaterial is more compressible than rocksalt, but also that the compressibility of CdS nanoparticles depends on their particle size. Furthermore, sintering of spherical nanoparticles into nanorods was observed for the 7.5 nm CdS nanoparticles. Our results provide new insights into the fundamental properties of nanoparticles under high pressure that will inform designs of new nanomaterial structures for emerging applications.

Electronic Phase Transitions in F-electron Metals at High Pressures: Synchrotron X-ray Spectroscopic Studies on GD to 100 GPa

2008 ◽  
Vol 1104 ◽  
Author(s):  
Choong-Shik Yoo ◽  
Brian Maddox ◽  
Valentin Iota
Keyword(s):  
High Pressure ◽  
Electronic Structure ◽  
Phase Transitions ◽  
Electron Correlation ◽  
High Pressures ◽  
Spectroscopic Studies ◽  
Strong Electron ◽  
X Ray ◽  
Volume Collapse ◽  
Highly Correlated

AbstractUnusual phase transitions driven by electron correlation effects occur in many f-electron metals (lanthanides and actinides alike) from localized phases to itinerant phases at high pressures. The dramatic changes in atomic volumes and crystal structures associated with some of these transitions signify equally important changes in the underlying electronic structure of these correlated f-electron metals. Yet, the relationships among the crystal structure, electronic correlation and electronic structure in f-electron metals have not been well understood. In this study, utilizing recent advances in third-generation synchrotron x-ray spectroscopies and high-pressure diamond-anvil cell technologies, we describe the pressure-induced spectral changes across the volume collapse transition in Gd at 60 GPa and well above. The spectral results suggest that the f-electrons of high-pressure Gd phases are highly correlated even at 100 GPa – consistent with the Kondo volume collapse model and the recent experimental evidence of strong electron correlation of α-Ce.

Size- and morphology-dependent structural transformations in anatase TiO2 nanowires under high pressures

2015 ◽  
Vol 93 (2) ◽  
pp. 165-172 ◽  
Author(s):  
Zhaohui Dong ◽  
Yang Song
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
High Pressures ◽  
Anatase Phase ◽  
X Ray Diffraction ◽  
Bulk Materials ◽  
Tio2 Nanowires ◽  
X Ray ◽  
Different Dimensions ◽  
Size And Morphology

Titanium dioxide (TiO2) nanowires with two different dimensions (i.e., <100 nm and ∼200 nm in diameter) were synthesized and studied under high pressure up to 37 GPa by Raman spectroscopy and synchrotron X-ray diffraction. Direct anatase to baddeleyite phase transitions were observed in both samples upon compression, but with different onset pressures. The observed phase transitions are in contrast to bulk TiO2, where the anatase phase transforms to α-PbO2 phase and then the baddeleyite phase. Compressibility of the anatase and baddeleyite phases was found different than both nanocrystals and the corresponding bulk materials. Our comparative study demonstrated not only that the morphology of TiO2 nanowire substantially influences the high pressure behaviors, but dimensions play a determining role in terms of transformation pressures, phase stability regions, and compressibility.

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