Induced ferromagnetic metallic state and Griffiths phase in La1/2Ca1/2Mn1−xMoxO3 compounds

2012 ◽  
Vol 136 (1) ◽  
pp. 254-258 ◽  
Author(s):  
J.W. Chen ◽  
G. Narsinga Rao
Keyword(s):  
Metallic State ◽  
Griffiths Phase

THE DYNAMICS OF DISORDERED MAGNETS IN THE GRIFFITHS PHASE, INVESTIGATED BY NEUTRON SCATTERING

1988 ◽  
Vol 49 (C8) ◽  
pp. C8-1047-C8-1048
Author(s):  
R. G. Lloyd ◽  
P. W. Mitchell ◽  
R. C. C. Ward ◽  
M. Cherrill
Keyword(s):  
Neutron Scattering ◽  
Griffiths Phase ◽  
Disordered Magnets

Emergence of size induced metallic state in the ferromagnetic insulating Pr0.8Sr0.2MnO3 manganite: Breaking of surface polarons

2015 ◽  
Vol 8 (2) ◽  
pp. 2084-2093 ◽  
Author(s):  
PROLOY TARAN DAS ◽  
Arun Kumar Nigam ◽  
Tapan Kumar Nath
Keyword(s):  
Transport Properties ◽  
Metallic State ◽  
Temperature Dependent ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
System A ◽  
Surface Disorder ◽  
Bulk System ◽  
Magnetic Transport ◽  
Grain Surface

Nano-dimensional effects on electronic-, magneto-transport properties of granular ferromagnetic insulating (FMI) Pr0.8Sr0.2MnO3 (PSMO) manganite (down to 40 nm) have been investigated in details. From the electronic and magnetic transport properties, a metallic state has been observed in grain size modulation by suppressing the ferromagnetic insulating state of PSMO bulk system. A distinct metal-insulator transition (MIT) temperature around 150 K has been observed in all nanometric samples. The observed insulator to metallic transition with size reduction can be explained with surface polaron breaking model, originates due to enhanced grain surface disorder. This proposed phenomenological polaronic model plays a significant role to understand the polaronic destabilization process on the grain surface regime of these phase separated nano-mangnatie systems. Temperature dependent resistivity and magnetoresistance data in presence of external magnetic fields are investigated in details with various compatible models.

scholarly journals Is Reduced Strontium Titanate a Semiconductor or a Metal?

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 744
Author(s):  
Christian Rodenbücher ◽  
Christo Guguschev ◽  
Carsten Korte ◽  
Sebastian Bette ◽  
Kristof Szot
Keyword(s):  
Point Defect ◽  
Decisive Role ◽  
Thermal Reduction ◽  
Defect Chemistry ◽  
Oxygen Activity ◽  
Metallic State ◽  
Metallic Behavior ◽  
Reducing Conditions ◽  
History Play ◽  
Semiconducting Behavior

In recent decades, the behavior of SrTiO3 upon annealing in reducing conditions has been under intense academic scrutiny. Classically, its conductivity can be described using point defect chemistry and predicting n-type or p-type semiconducting behavior depending on oxygen activity. In contrast, many examples of metallic behavior induced by thermal reduction have recently appeared in the literature, challenging this established understanding. In this study, we aim to resolve this contradiction by demonstrating that an initially insulating, as-received SrTiO3 single crystal can indeed be reduced to a metallic state, and is even stable against room temperature reoxidation. However, once the sample has been oxidized at a high temperature, subsequent reduction can no longer be used to induce metallic behavior, but semiconducting behavior in agreement with the predictions of point defect chemistry is observed. Our results indicate that the dislocation-rich surface layer plays a decisive role and that its local chemical composition can be changed depending on annealing conditions. This reveals that the prediction of the macroscopic electronic properties of SrTiO3 is a highly complex task, and not only the current temperature and oxygen activity but also the redox history play an important role.

An interpretation on the thermodynamic properties of liquid Pb–Te alloys

2020 ◽  
Vol 39 (1) ◽  
pp. 297-303
Author(s):  
Toru Akasofu ◽  
Masanobu Kusakabe ◽  
Shigeru Tamaki
Keyword(s):  
Thermodynamic Properties ◽  
Electron Affinity ◽  
Ionization Energy ◽  
Narrow Band ◽  
Structural Information ◽  
Lead Telluride ◽  
Liquid Lead ◽  
Metallic State ◽  
Ternary Solution ◽  
Conduction Electrons

AbstractThe bonding character of liquid lead telluride \text{PbTe} is thermodynamically investigated in detail. Its possibility as an ionic melt composed of cation {\text{Pb}}^{2+} and anion {\text{Te}}^{2-} is not acceptable, by comparing the ionization energy of \text{Pb} atom, electron affinity of \text{Te} atom and the ionic bonding energy due to the cation {\text{Pb}}^{2+} and anion {\text{Te}}^{2-} with the help of structural information. Solid lead telluride PbTe as a narrow band gap semiconductor might yield easily the overlapping of the tail of valence band and that of conduction one. And on melting, it becomes to an ill-conditioned metallic state, which concept is supported by the electrical behaviors of liquid Pb–Te alloys observed by the present authors. As structural information tells us about the partial remain of some sorts of covalent-type mono-dipole and poly-dipole of the molecule \text{PbTe}, all systems are thermodynamically explained in terms of a mixture of these molecules and cations {\text{Pb}}^{4+} and {\text{Te}}^{2+} and a small amount of the conduction electrons are set free from these elements based on the ternary solution model.

scholarly journals Investigating the Effects of Surface Adsorbates on Gold and Palladium Deposition on Carbon

2021 ◽  
Author(s):  
Bethany Bowden ◽  
Josh A. Davies-Jones ◽  
Matthew Davies ◽  
Philip R. Davies ◽  
David J. Morgan ◽  
...  
Keyword(s):  
Aqueous Solutions ◽  
Ammonium Hydroxide ◽  
Ammonium Ion ◽  
Metallic State ◽  
Chloroauric Acid ◽  
Final State ◽  
Ammonium Thiosulfate ◽  
Surface Adsorbates ◽  
Surface Hydroxyls ◽  
High Concentrations

AbstractSurface functional groups have a strong influence on the deposition and final state of nanoparticles adsorbed on to the surface, a role discussed by Professor Spencer in his work. This tribute to Spencer explores the formation of hydroxyls, thiosulfates, sulfites and sulfur atoms on carbon (HOPG) surfaces and their effect on the deposition of gold and palladium from aqueous solutions. Hydroxyls formed from ammonium hydroxide treatment have identical behaviour to those formed by acid treatment, and gold adsorption from Au3+ solutions gives Au0 initially, with Au3+ formed at higher concentrations on these surfaces. In contrast, palladium adsorption is hindered by the presence of the hydroxyls and there is no indication of any reduction to the metallic state. Ammonium thiosulfate adsorbs dissociatively from aqueous solutions on HOPG if the surface is pre-activated by the presence of surface hydroxyls. At low concentrations of ammonium thiosulfate, adsorbed sulfite and sulfur are formed in equimolar concentrations whereas adsorption of high concentrations of ammonium thiosulfate gives some degree of molecular adsorption, with evidence in XP spectra for an ammonium ion and a sulfur 2p peak at 282.9 eV attributed to the undissociated thiosulfate ion. Both sulfur and the sulfite are stable at the surface in neutral solutions but the sulfite desorbs when treated with acidified solutions (~ pH ≤ 6). These two groups are also stable at 373 K but begin to desorb by 473 K. Exposure to a weak chloroauric acid solution causes the desorption of the sulfite and formation of a gold species with an XP binding energy of 84.6 eV; we cannot determine from the present data whether this peak is due to a Au(I) state or very small nanoparticles of Au(0). Graphic Abstract

scholarly journals Epidemic growth and Griffiths effects on an emergent network of excited atoms

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
T. M. Wintermantel ◽  
M. Buchhold ◽  
S. Shevate ◽  
M. Morgado ◽  
Y. Wang ◽  
...  
Keyword(s):  
Complex Systems ◽  
Power Laws ◽  
Excitation Density ◽  
Griffiths Phase ◽  
Many Body ◽  
Excited Atoms ◽  
Equilibrium Dynamics ◽  
Many Body Systems ◽  
Excitation Number ◽  
Non Equilibrium

AbstractWhether it be physical, biological or social processes, complex systems exhibit dynamics that are exceedingly difficult to understand or predict from underlying principles. Here we report a striking correspondence between the excitation dynamics of a laser driven gas of Rydberg atoms and the spreading of diseases, which in turn opens up a controllable platform for studying non-equilibrium dynamics on complex networks. The competition between facilitated excitation and spontaneous decay results in sub-exponential growth of the excitation number, which is empirically observed in real epidemics. Based on this we develop a quantitative microscopic susceptible-infected-susceptible model which links the growth and final excitation density to the dynamics of an emergent heterogeneous network and rare active region effects associated to an extended Griffiths phase. This provides physical insights into the nature of non-equilibrium criticality in driven many-body systems and the mechanisms leading to non-universal power-laws in the dynamics of complex systems.

scholarly journals Facile Synthesis of COF-Supported Reduced Pd-Based Catalyst for One-Pot Reductive Amination of Aldehydes

Catalysts ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 287
Author(s):  
Jianguo Liu ◽  
Mingyue Zhang ◽  
Longlong Ma
Keyword(s):  
Heterogeneous Catalysts ◽  
Reductive Amination ◽  
Secondary Amines ◽  
Metallic State ◽  
One Pot ◽  
Effective Synthesis ◽  
Pharmaceutical Industries ◽  
The One ◽  
Heterocyclic Aldehydes ◽  
Supported Pd

Dibenzylamine motifs are an important class of crucial organic compounds and are widely used in fine chemical and pharmaceutical industries. The development of the efficient, economical, and environmentally friendly synthesis of amines using transition metal-based heterogeneous catalysts remains both desirable and challenging. Herein, we prepared the covalent organic framework (COF)-supported heterogeneous reduced COF-supported Pd-based catalyst and used it for the one-pot reductive amination of aldehydes. There are both Pd metallic state and oxidated Pdσ+ in the catalysts. Furthermore, in the presence of the reduced COF-supported Pd-based catalyst, many aromatic, aliphatic, and heterocyclic aldehydes with various functional groups substituted were converted to their corresponding amines products in good to excellent selectivity (up to 91%) under mild reaction conditions (70 °C, 2 h, NH3, 20 bar H2). This work expands the covalent organic frameworks for the material family and its support catalyst, opening up new catalytic applications in the economical, practical, and effective synthesis of secondary amines.

Pressure-induced unusual metallic state inEuNiO3

2015 ◽  
Vol 91 (19) ◽  
Author(s):  
Hisao Kobayashi ◽  
Shugo Ikeda ◽  
Yoshitaka Yoda ◽  
Naohisa Hirao ◽  
Yasuo Ohishi ◽  
...  
Keyword(s):  
Metallic State

Carbon Nanotunes Supported Pt and Pt-Ru Catalysts for Selective Hydrogenation of Citral: Effect of Promoters and Thermal Activation of Catalysts

2012 ◽  
Vol 584 ◽  
pp. 229-233 ◽  
Author(s):  
Sakunthala Angamuthu Ananthan ◽  
Narayanan Vengidusamy ◽  
Krishnamoorthy Giribabu ◽  
Ranganathan Suresh
Keyword(s):  
Selective Hydrogenation ◽  
Bimetallic Catalyst ◽  
Surface Group ◽  
Inert Atmosphere ◽  
Area Measurement ◽  
Bet Surface Area ◽  
Metallic State ◽  
Environment Friendly ◽  
Ru Catalysts ◽  
Different Temperatures

MWCNT supported Pt, Ru, and Pt–Ru catalysts were prepared and reduced at two different temperatures, 375°C (LTR) and 675°C (HTR) for the selective hydrogenation of citral to the corresponding unsaturated alcohols (geraniol and nerol). The catalysts were characterized by BET Surface area measurement, TPD, SEM, EDAX, TEM, XRD and XPS. It was found that the XRD of Pt and Ru shows fcc and hcp crystalline structure respectively, which is uniformly dispersed with an average particles size of 3.5 nm and zero valence metallic state. The removal of acidic oxygen surface group is observed when heat- treatments in a inert atmosphere at 675°C were performed. The bimetallic catalyst of Pt-Ru/MWCNT (HTR) was found to afford remarkably high conversion levels (85%) and high selectivity (95%) provided that a thermal pretreatment was performed on the catalyst. These results can be rationalized in terms of electron transfer from the support to the metal. The catalysts are environment friendly and can be recycled for more than eight times.

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