Resistance anomaly and structural disorder in NiSi2 under high pressure

2007 ◽  
Vol 68 (3) ◽  
pp. 367-372 ◽  
Author(s):  
Alka B. Garg ◽  
V. Vijayakumar ◽  
A.K. Verma ◽  
R.S. Rao ◽  
B.K. Godwal
Keyword(s):  
High Pressure ◽  
Structural Disorder ◽  
Resistance Anomaly

scholarly journals Impact of Alkali Ions Codoping on Magnetic Properties of La0.9A0.1Mn0.9Co0.1O3 (A: Li, K, Na) Powders and Ceramics

2020 ◽  
Vol 10 (24) ◽  
pp. 8786
Author(s):  
Paweł Głuchowski ◽  
Ruslan Nikonkov ◽  
Robert Tomala ◽  
Wiesław Stręk ◽  
Tatsiana Shulha ◽  
...  
Keyword(s):  
High Pressure ◽  
Magnetic Properties ◽  
Exchange Interactions ◽  
Structural Disorder ◽  
Subsequent Increase ◽  
Cobalt Ions ◽  
X Ray ◽  
Alkali Ions ◽  
High Pressure Sintering ◽  
Combustion Technique

The aim of the work was to check how the introduction of alkali and cobalt ions into a manganese structure can affect the structural disorder and, in consequence, lead to the changes (improvements) of magnetic properties. The high-pressure sintering technique was applied to check if the external factor can modify the magnetization of manganites. Nanocrystalline La0.9A0.1Mn0.9Co0.1O3 (where A is Li, K, Na) powders were synthesized by the combustion technique. The respective powders were used for nanoceramics preparation by the high-pressure sintering technique. The structure and morphology of the compounds were studied by X-ray powder diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Magnetization studies for all compounds were performed in order to check the changes induced by either codoping or the sintering pressure. It was found that the type of the dopant ion and sintering pressure produced significant changes to the magnetic properties of the studied compounds. Alkali ions lead to the stabilization of Co ions in the +2 oxidation state and the formation of positive exchange interactions Mn3+–Mn4+ and Co2+–Mn4+ and the subsequent increase in remanent magnetization. High sintering pressure leads to a decrease in grain size and reduction of long-range ferromagnetic order and lower magnetization.

Myrmekitic intergrowth of tourmaline and quartz in eclogite-hosting gneisses of the Tso Morari ultrahigh-pressure metamorphic terrane (Eastern Ladakh, India): a possible record of high-pressure conditions

2019 ◽  
Vol 481 (1) ◽  
pp. 175-194 ◽  
Author(s):  
Igor Broska ◽  
Peter Bačík ◽  
Santosh Kumar ◽  
Marian Janák ◽  
Sergiy Kurylo ◽  
...  
Keyword(s):  
High Pressure ◽  
Early Stage ◽  
Structural Disorder ◽  
Ultrahigh Pressure ◽  
Crystalline Complex ◽  
Ladakh Himalaya ◽  
Metamorphic Terrane ◽  
First Time ◽  
Tso Morari

AbstractAlkaline schorlitic tourmaline with domains of myrmekitic quartz and tourmaline intergrowths is reported for the first time from quartzo-feldspathic gneisses of the Tso Morari Crystalline Complex (TMCC), eastern Ladakh Himalaya. Except for schorlitic tourmaline, the brown-green dravitic tourmaline occurs in melanocratic layers of the gneiss. The schorlitic tourmaline contains REE-rich apatite, which is a typical mineral formed under high-pressure (HP) conditions. The observed myrmekite, marked by vermicular quartz and tourmaline intergrowths, was probably formed during decompression as a consequence of excess silica released from recrystallized tourmaline. The recalculated composition of the tourmaline with quartz myrmekite suggests that Si also occupied the tourmaline octahedral Z site during the HP regime. During decompression excess Si from this tourmaline was replaced by Mg and Fe3+. At an early stage of exhumation needle-shaped schorlitic tourmaline II and mosaic zoning were formed. The excess of silica and the structural disorder suggest that the Si-oversaturated tourmaline was stable at high-pressure–ultrahigh-pressure (HP–UHP) conditions. The greater stability of dravitic tourmaline compared to schorlitic tourmaline at HP conditions is evidently recorded at the TMCC. The tourmaline-bearing gneisses of the TMCC most probably shared the same metamorphic conditions during Tertiary collision of the Indian and Eurasian plates, similar to that observed for the associated UHP eclogites.

scholarly journals High-Pressure Crystal Structure and Unusual Magnetoresistance of a Single-Component Molecular Conductor [Pd(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate)

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 534
Author(s):  
Hengbo Cui ◽  
Hamish H.-M. Yeung ◽  
Yoshitaka Kawasugi ◽  
Takaaki Minamidate ◽  
Lucy K. Saunders ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Three Dimensional ◽  
Structural Disorder ◽  
Electron System ◽  
Experimental Information ◽  
Crystal Structure Analysis ◽  
Single Component ◽  
Unusual Behavior ◽  
Dirac Electron

A single-component molecular crystal [Pd(dddt)2] has been shown to exhibit almost temperature-independent resistivity under high pressure, leading theoretical studies to propose it as a three-dimensional (3D) Dirac electron system. To obtain more experimental information about the high-pressure electronic states, detailed resistivity measurements were performed, which show temperature-independent behavior at 13 GPa and then an upturn in the low temperature region at higher pressures. High-pressure single-crystal structure analysis was also performed for the first time, revealing the presence of pressure-induced structural disorder, which is possibly related to the changes in resistivity in the higher-pressure region. Calculations based on the disordered structure reveal that the Dirac cone state and semiconducting state coexist, indicating that the electronic state at high pressure is not a simple Dirac electron system as previously believed. Finally, the first measurements of magnetoresistance on [Pd(dddt)2] under high pressure are reported, revealing unusual behavior that seems to originate from the Dirac electron state.

Li2Pt3Se4: a new lithium platinum selenide with jaguéite-type crystal structure by multianvil high-pressure/high-temperature synthesis

2016 ◽  
Vol 71 (11) ◽  
pp. 1095-1104 ◽  
Author(s):  
Gunter Heymann ◽  
Elisabeth Selb
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Transition Metal ◽  
Single Crystal ◽  
Structural Disorder ◽  
Stoichiometric Ratio ◽  
Mineral Phases ◽  
High Temperature Synthesis ◽  
Transition Metal Atoms ◽  
High Pressure High Temperature

AbstractThe monoclinic lithium platinum selenide Li2Pt3Se4 was obtained via a multianvil high-pressure/high-temperature route at 8 GPa and 1200°C starting from a stoichiometric mixture of lithium nitride, selenium, and platinum. The structure of the ternary alkali metal-transition metal-selenide was refined from single-crystal X-ray diffractometer data: P21/c (no. 14), a=525.9(2), b=1040.6(2), c=636.5(2) pm, β=111.91(1)°, R1=0.0269, wR2=0.0569 (all data) for Li2Pt3Se4. Furthermore, the isostructural mineral phases jaguéite (Cu2Pd3Se4) and chrisstanleyite (Ag2Pd3Se4) were reinvestigated in their ideal stoichiometric ratio. The syntheses of the mineral phases were also carried out under multianvil conditions. Single-crystal data revealed a hitherto not described structural disorder of the transition metal atoms.

Refractory semiconductor of boron phosphide

1990 ◽  
Vol 5 (12) ◽  
pp. 2933-2947 ◽  
Author(s):  
Y. Kumashiro
Keyword(s):  
High Pressure ◽  
Thermal Neutron ◽  
Ion Irradiation ◽  
Schottky Diodes ◽  
Chemical Vapor ◽  
Structural Disorder ◽  
Flux Method ◽  
Boron Phosphide ◽  
Thermal Neutron Irradiation ◽  
Donor And Acceptor

The single crystal growth of boron phosphide (BP) by employing the high pressure flux method and chemical vapor deposition (CVD) process is described together with characterization of the prepared BP and its electrical, thermal, semiconducting, and electrochemical properties. BP single crystals prepared by the high pressure flux method contain copper used as the flux, but they are promising for photocathode materials. BP single crystalline wafers prepared by the CVD process using Si wafer substrate contained autodoped silicon with the concentration of 1018−1020 atoms·cm−3, depending on the growth temperature and the substrate plane. The Si atoms which act as acceptors are incorporated at phosphorus sites in BP. The lattice constants determined by the Bond method explain the conduction type of BP. Some electronic transport properties such as donor and acceptor levels and lattice scattering process before and after thermal neutron experiments are clarified. The thermal conduction is limited by three-phonon processes. The formation of defects by thermal neutron irradiation and that of structural disorder by ion-irradiation are mentioned. Schottky diodes consisting of n–BP and Sb or n–BP and Au, which are denoted as n–BP–Sb and –Au, respectively, show excellent characteristics, and their barrier heights are independent of metals and two-thirds of energy bandgap, expected from the surface-state model. Finally, recent results on thermoelectric properties of sintered specimens are mentioned.

Influence of high pressure on Tc and normal state resistance anomaly of κ−(BEDTTTF)2Cu[N(CN)2]Br

1991 ◽  
Vol 185-189 ◽  
pp. 2681-2682 ◽  
Author(s):  
Yu.V. Sushko ◽  
V.A. Bondarenko ◽  
R.A. Petrosov ◽  
N.D. Kushch ◽  
E.B. Yagubskii ◽  
...  
Keyword(s):  
High Pressure ◽  
Normal State ◽  
State Resistance ◽  
Normal State Resistance ◽  
Resistance Anomaly

Measurement and Reduction of Radiation Damage in Frozen Hydrated Crystalline Specimens

1978 ◽  
Vol 36 (3) ◽  
pp. 70-77 ◽  
Author(s):  
R.M. Glaeser ◽  
S.B. Hayward
Keyword(s):  
Diffraction Pattern ◽  
Structural Information ◽  
Structural Disorder ◽  
Structural Features ◽  
Biological Macromolecules ◽  
Diffraction Intensity ◽  
Object Structure ◽  
Specimen Material ◽  
Unit Cells ◽  
Identical Unit

Highly ordered or crystalline biological macromolecules become severely damaged and structurally disordered after a brief electron exposure. Evidence that damage and structural disorder are occurring is clearly given by the fading and eventual disappearance of the specimen's electron diffraction pattern. The fading and disappearance of sharp diffraction spots implies a corresponding disappearance of periodic structural features in the specimen. By the same token, there is a oneto- one correspondence between the disappearance of the crystalline diffraction pattern and the disappearance of reproducible structural information that can be observed in the images of identical unit cells of the object structure. The electron exposures that result in a significant decrease in the diffraction intensity will depend somewhat upon the resolution (Bragg spacing) involved, and can vary considerably with the chemical makeup and composition of the specimen material.

High-pressure freezing of cells in suspension for low-voltage scanning electron microscopy (LVSEM)

1991 ◽  
Vol 49 ◽  
pp. 64-65
Author(s):  
Marek Malecki ◽  
James Pawley ◽  
Hans Ris
Keyword(s):  
Electron Microscopy ◽  
High Pressure ◽  
Low Voltage ◽  
Culture Media ◽  
Cell Structure ◽  
Freeze Substitution ◽  
Ice Crystal ◽  
High Pressure Freezing ◽  
Cell Culture Media ◽  
Voltage Scanning

The ultrastructure of cells suspended in physiological fluids or cell culture media can only be studied if the living processes are stopped while the cells remain in suspension. Attachment of living cells to carrier surfaces to facilitate further processing for electron microscopy produces a rapid reorganization of cell structure eradicating most traces of the structures present when the cells were in suspension. The structure of cells in suspension can be immobilized by either chemical fixation or, much faster, by rapid freezing (cryo-immobilization). The fixation speed is particularly important in studies of cell surface reorganization over time. High pressure freezing provides conditions where specimens up to 500μm thick can be frozen in milliseconds without ice crystal damage. This volume is sufficient for cells to remain in suspension until frozen. However, special procedures are needed to assure that the unattached cells are not lost during subsequent processing for LVSEM or HVEM using freeze-substitution or freeze drying. We recently developed such a procedure.

Prolonged Fixation Studies For Spaceflight

1973 ◽  
Vol 31 ◽  
pp. 332-333
Author(s):  
Robert Corbett ◽  
Delbert E. Philpott ◽  
Sam Black
Keyword(s):  
High Pressure ◽  
Living Systems ◽  
Prolonged Storage ◽  
Time Intervals ◽  
Early Signs ◽  
Large Numbers

Observation of subtle or early signs of change in spaceflight induced alterations on living systems require precise methods of sampling. In-flight analysis would be preferable but constraints of time, equipment, personnel and cost dictate the necessity for prolonged storage before retrieval. Because of this, various tissues have been stored in fixatives and combinations of fixatives and observed at various time intervals. High pressure and the effect of buffer alone have also been tried.Of the various tissues embedded, muscle, cartilage and liver, liver has been the most extensively studied because it contains large numbers of organelles common to all tissues (Fig. 1).

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