Dehydration and decomposition of pyrophyllite at high pressures: electrical conductivity and X-ray diffraction studies to 5 GPa

1997 ◽  
Vol 34 (6) ◽  
pp. 875-882 ◽  
Author(s):  
Tara L. Hicks ◽  
Richard A. Secco
Keyword(s):  
Electrical Conductivity ◽  
South African ◽  
Pressure Dependence ◽  
High Pressures ◽  
Ionic Conduction ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Dependence Of Conductivity

The dehydration and decomposition of South African pyrophyllite were studied in the pressure range 2.5–5.0 GPa and in the temperature (T) range 295–1473 K using both in situ electrical conductivity measurements and X-ray diffraction studies on the recovered samples. Activation energies for conduction (Qc) vary in the range 0.02–0.07 eV for T ≤ 500 K where the dominant conduction mode is electronic, and Qc is in the range 1.10–1.28 eV for T ≥ 500 K where ionic conduction dominates. Abrupt changes in the isobaric temperature dependence of conductivity mark the onset of dehydration and subsequent decomposition into kyanite plus quartz–coesite. At 2.5 GPa, South African pyrophyllite forms the dehydroxylate phase at 760 K with a pressure dependence of ~30 K/GPa and complete decomposition follows at 1080 K with a pressure dependence of ~41 K/GPa. The resulting pressure–temperature phase diagram is in very good agreement with many previous studies at 1 atm (101.325 kPa).

Electrical Resistivity of Three Polymorphs of Basi2 and P-T Phase Diagram

1995 ◽  
Vol 402 ◽  
Author(s):  
M. Imai ◽  
T. Hirano
Keyword(s):  
Phase Diagram ◽  
Electrical Resistivity ◽  
High Pressures ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Resistivity Measurements ◽  
Type Semiconductor ◽  
T Phase

AbstractThis paper reports a pressure-temperature phase diagram for BaSi2 and evaluates the electrical resistivity of orthorhombic, cubic and trigonal BaSi2. In-situ X-ray diffraction measurements revealed the transition sequence of cubic and trigonal BaSi2 from orthorhombic BaSi2 at high pressures and high temperatures. The electrical resistivity measurements of three polymorphs show that the electrical properties depend on the crystal structure: orthorhombic BaSi2is an n-type semiconductor as previously reported; cubic BaSi2is an n-type semiconductor; trigonal BaSi2is a hole metal that shows superconductivity with an onset temperature of 6.8K.

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 Time-Resolved X-Ray Diffraction Investigation of the ω→ψ Transition in Al-Cu-Fe Quasicrystal-Forming Alloys

2007 ◽  
Vol 558-559 ◽  
pp. 943-947 ◽  
Author(s):  
E. Otterstein ◽  
R. Nicula ◽  
J. Bednarčík ◽  
M. Stir ◽  
E. Burkel
Keyword(s):  
Large Scale ◽  
Applied Pressure ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Time Resolved ◽  
X Ray ◽  
In Situ Xrd ◽  
Kinetics Of

Quasicrystals are aperiodic long-range ordered solids with a high potential for many modern applications. Interest is nowadays paid to the development of economically viable large-scale synthesis procedures of quasicrystalline materials involving solid-state transformations. The kinetics of the high-temperature phase transition from the complex ω-phase to the icosahedral quasicrystalline (iQC) ψ-phase in AlCuFe nanopowders was here examined by in-situ time-resolved X-ray diffraction experiments using synchrotron radiation. In-situ XRD experiments will allow insight on the influence of uniaxial applied pressure on the kinetics of phase transitions leading to the formation of single-phase QC nanopowders and further contribute to the optimization of sintering procedures for nano-quasicrystalline AlCuFe alloy powders.

scholarly journals The solvothermal synthesis of γ-AlOOH nanoflakes and their compression behaviors under high pressures

RSC Advances ◽  
2017 ◽  
Vol 7 (9) ◽  
pp. 4904-4911 ◽  
Author(s):  
Xudong Zhou ◽  
Jian Zhang ◽  
Yanmei Ma ◽  
Hui Tian ◽  
Yue Wang ◽  
...  
Keyword(s):  
High Pressure ◽  
Synchrotron Radiation ◽  
Solvothermal Synthesis ◽  
High Pressures ◽  
X Ray Diffraction ◽  
X Ray ◽  
Radiation Angle

The compression behaviors of γ-AlOOH nanoflakes were investigated via in situ high pressure synchrotron radiation angle dispersive X-ray diffraction techniques.

IV. Order–disorder transitions: solid state kinetics, thermal analyses, X-ray diffraction and electrical conductivity studies in the Ag2SO4–K2SO4 system

1985 ◽  
Vol 63 (2) ◽  
pp. 324-328 ◽  
Author(s):  
M. Sunitha Kumari ◽  
Etalo A. Secco
Keyword(s):  
Electrical Conductivity ◽  
High Temperature ◽  
Reaction Kinetics ◽  
Solid Phase ◽  
Thermal Analyses ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Solid Liquid

Order–disorder transitions occurring in the Ag2SO4–K2SO4 system were investigated by reaction kinetics, thermal analyses, X-ray diffraction, and electrical conductivity techniques. Solid–liquid and solid–solid phase diagrams are reported.The conductivity data in the high temperature phase of the solid resemble superionic conductivity behavior. The higher conductivity of Ag2SO4 with K+ presence relative to pure Ag2SO4 and Ag2−xNaxSO4 compositions support a lattice expansion facilitating higher mobility of ions.The reaction kinetics, X-ray diffraction, and electroconductivity results suggest a relatively open periodic [Formula: see text] sublattice in the high-temperature phase of the sulfate-based systems studied in this series.

scholarly journals In situ X-ray diffraction of silicate liquids and glasses under dynamic and static compression to megabar pressures

2020 ◽  
Vol 117 (22) ◽  
pp. 11981-11986 ◽  
Author(s):  
Guillaume Morard ◽  
Jean-Alexis Hernandez ◽  
Marco Guarguaglini ◽  
Riccardo Bolis ◽  
Alessandra Benuzzi-Mounaix ◽  
...  
Keyword(s):  
Structural Changes ◽  
High Pressures ◽  
Silicate Glasses ◽  
X Ray Diffraction ◽  
Static Compression ◽  
X Ray ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Silicate Liquids

Properties of liquid silicates under high-pressure and high-temperature conditions are critical for modeling the dynamics and solidification mechanisms of the magma ocean in the early Earth, as well as for constraining entrainment of melts in the mantle and in the present-day core–mantle boundary. Here we present in situ structural measurements by X-ray diffraction of selected amorphous silicates compressed statically in diamond anvil cells (up to 157 GPa at room temperature) or dynamically by laser-generated shock compression (up to 130 GPa and 6,000 K along the MgSiO3glass Hugoniot). The X-ray diffraction patterns of silicate glasses and liquids reveal similar characteristics over a wide pressure and temperature range. Beyond the increase in Si coordination observed at 20 GPa, we find no evidence for major structural changes occurring in the silicate melts studied up to pressures and temperatures exceeding Earth’s core mantle boundary conditions. This result is supported by molecular dynamics calculations. Our findings reinforce the widely used assumption that the silicate glasses studies are appropriate structural analogs for understanding the atomic arrangement of silicate liquids at these high pressures.

Transformation from molecular to polymeric nitrogen at high pressures and temperatures: In situ x-ray diffraction study

2008 ◽  
Vol 93 (9) ◽  
pp. 091907 ◽  
Author(s):  
I. A. Trojan ◽  
M. I. Eremets ◽  
S. A. Medvedev ◽  
A. G. Gavriliuk ◽  
V. B. Prakapenka
Keyword(s):  
Diffraction Study ◽  
High Pressures ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Pressures And Temperatures ◽  
Polymeric Nitrogen
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