EFFECTS OF THE Al CONTENT IN MgB2: A RAMAN STUDY

2003 ◽  
Vol 17 (04n06) ◽  
pp. 505-511 ◽  
Author(s):  
P. DORE ◽  
P. POSTORINO ◽  
A. CONGEDUTI ◽  
A. NUCARA ◽  
A. BIANCONI ◽  
...  
Keyword(s):  
Partial Substitution ◽  
Superconducting Transition ◽  
Coupling Constant ◽  
X Ray Diffraction ◽  
Progressive Reduction ◽  
Al Content ◽  
Electron Phonon Coupling ◽  
Raman Study ◽  
High Al Content ◽  
Raman Active Phonon

The partial substitution of Al for Mg in the MgB2 superconductor produces both a progressive reduction of its superconducting transition temperature Tc and the occurrence of two distinct structural phases at low and high Al content, as shown by X-ray diffraction data. To achieve a deeper understanding of the effect of the Al content, we investigated the x dependence of the Raman phonon spectrum in Mg1-xAlxB2 compounds. We analyze the evolution of the E2g Raman-active phonon mode observed on increasing x both in our measurements (0 ≤ x ≤ 0.5) and in recent experiments (0 ≤ x ≤ 1). Our analysis shows the connection between the evolution with x of the E2g phonon and the Tc suppression, thus supporting the hypothesis that superconductivity in MgB2 is mediated by a strong e-ph coupling with the E2g mode. We then derive the electron-phonon coupling constant λ in the 0-0.5 x range.

First-principles prediction of superconductivity in LiBSi1-xAlx

2015 ◽  
Vol 29 (12) ◽  
pp. 1550064
Author(s):  
Rende Miao ◽  
Jun Yang ◽  
Zhong Bai ◽  
Dan Can ◽  
Xi Zhang ◽  
...  
Keyword(s):  
First Principles ◽  
Partial Substitution ◽  
Hole Doping ◽  
Superconducting Transition ◽  
Coupling Constant ◽  
Superconducting Properties ◽  
Virtual Crystal Approximation ◽  
Phonon Spectra ◽  
Electron Phonon Coupling ◽  
Formation Energies

Electronic structure, lattice dynamics and superconducting properties for theoretically devised superconductor LiBSi 1-x Al x are obtained by first-principles calculations. We assume that Lithium Boron Silicon ( LiBSi ) has the same crystal structure as that of Lithium borocarbide ( LiBC ). The pristine LiBSi is predicted to be a zero-gap semiconductor. Hole doping of LiBSi through partial substitution of Si by SiAl atoms can produce a semiconductor–metal transition and develop superconductivity. To assess the thermodynamic stability of LiBSi 1-x Al x, the formation energies are calculated using the supercell method. For LiBSi 0.75 Al 0.25 and LiBSi 0.875 Al 0.125, the obtained formation energies are -5.9 and -6.1 eV, respectively, indicating that LiBSi 1-x Al x is energetically favorable at least in the range of 0 ≤ x ≤ 0.25. Phonon spectra and superconducting properties are obtained within the virtual-crystal approximation (VCA) treatment. The results show that LiBSi 1-x Al x is dynamically stable approximately in the range of 0 ≤ x ≤ 0.35. For LiBSi 0.8 Al 0.2, the obtained electron-phonon coupling constant λ is 0.86 and superconducting transition temperature TC is predicted to be in the range of 11–13 K (0.14 ≥ μ* ≥ 0.1).

Microstructure and Distribution of Low Content Elements in AlNiCo 9

2017 ◽  
Vol 898 ◽  
pp. 1669-1674 ◽  
Author(s):  
Bin Shao ◽  
Bing Bing Li ◽  
Chun Hong Li ◽  
Yi Long Ma ◽  
Qiang Zheng ◽  
...  
Keyword(s):  
Magnetic Force ◽  
Magnetic Domain ◽  
Magnetic Force Microscope ◽  
X Ray Diffraction ◽  
Rich Phase ◽  
X Ray ◽  
Al Content ◽  
Transmission Electron ◽  
Titanium Sulfide ◽  
High Al Content

The microstructure and the chemistry distribution of AlNiCo 9 samples were characterized by the X-ray diffraction, magnetic force microscope, field emission scanning electron microscopy and transmission electron microscope. An interface of a high Al content was formed near the FeCo-rich phases with a size of about 30 nm. S elements mainly combined with Ti to form titanium sulfide bars with the length between 70-150 μm, while S elements was not confirmed in the nanostructured FeCo-rich phase and AlNi-rich phase. Si and Nb preferably existed in the NiAl-rich phase, and a higher content Nb near the Cu precipitate boundary was observed. Moreover, the magnetic domain structure of AlNiCo 9 was also studied.

Electron–phonon coupling constant and critical temperature of binary and ternary superconducting alloys of V, Nb, Mo, and Ta

1980 ◽  
Vol 58 (9) ◽  
pp. 1383-1387 ◽  
Author(s):  
Parsathi Chatterjee
Keyword(s):  
Superconducting Transition ◽  
Matrix Approximation ◽  
Body Centered Cubic ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Transition Elements ◽  
Electron Phonon Coupling ◽  
Exchange Approximation ◽  
Cubic Structure ◽  
Substitutional Alloys

A modified version of the theory of Gaspari and Gyorffy for calculating the electron–phonon coupling constant, λ, for binary substitutional alloys has been used in conjunction with McMillan's expression as modified by Dynes for the superconducting transition temperature, Tc, to obtain λ and Tc for the substitutional alloys NbTa, NbV, VMo, VTa, and TaMo. The theory has been further extended via the Average T-matrix Approximation to calculate λ and Tc for the ternary alloy, NbTaMo, having the same body-centered cubic structure as its components. The calculations of λ are based on self-consistent APW or KRR band structure data for the transition elements V, Nb, Mo, and Ta, obtained by using either Xα or the Hedin–Lundqvist version of the [Formula: see text] exchange approximation to calculate the potentials. The results thus obtained at different concentrations agree favourably with experiments for NbTa, NbV, VMo, and VTa. For TaMo and NbTaMo, for which experimental data on Tc are not yet available, we predict that they are fairly good superconductors.

Damage and Lattice Strain in Ion-Irradiated AlxGai-xAs

1994 ◽  
Vol 354 ◽  
Author(s):  
P. Partyka ◽  
R.S. Averback ◽  
D.V. Forbes ◽  
J.J. Coleman ◽  
P. Ehrhart ◽  
...  
Keyword(s):  
Rutherford Backscattering Spectrometry ◽  
Lattice Parameter ◽  
Large Strains ◽  
X Ray Diffraction ◽  
Al Content ◽  
Plane Lattice ◽  
Transmission Electron ◽  
Out Of Plane ◽  
Radiation Induced ◽  
High Al Content

AbstractRadiation-induced damage and strain in AlxGai-xAs (x=5 to 1) were investigated by measurements of the lattice parameter using x-ray diffraction. Irradiations employed MeV C, Ar and Au ion beams with a substrate temperature of 80 K. For samples with high Al content, the out-of-plane lattice parameter increased with fluence at low doses, saturated, and then decreased to nearly its original value. The in-plane lattice parameter did not change, throughout. These results were independent of the irradiation particle when scaled by damage energy. For the Al.5Ga.5As samples, however, the out-of-plane lattice parameter increased monotonically with dose to large strains until the layer amorpnized. Selected samples were examined by high resolution and conventional transmission electron microscopy (TEM). Channeling Rutherford backscattering spectrometry (CRBS) was also employed to monitor the buildup of damage in many samples. Recovery of the lattice parameter during subsequent thermal annealing was also investigated.

Magnetotransport and Structural Properties of Nanocrystalline FeAgAl Thin Films

2008 ◽  
Vol 8 (8) ◽  
pp. 4068-4072 ◽  
Author(s):  
P. B. Patil ◽  
S. Rout ◽  
A. R. B. Rao ◽  
M. Senthil Kumar
Keyword(s):  
Thin Films ◽  
Average Particle Size ◽  
Partial Substitution ◽  
Average Particle ◽  
X Ray Diffraction ◽  
Al Content ◽  
Transmission Electron ◽  
Standard Value ◽  
Magnetoresistance Ratio ◽  
Xrd Patterns

Structural and magnetotransport properties of metallic FexAgyAlz nanogranular thin films were studied. These films with several compositions were prepared by dc magnetron sputtering. X-ray diffraction (XRD) measurements carried out on the samples show only Ag(111) peaks. The d-spacings determined from the Ag(111) peaks are smaller than the standard value for bulk Ag indicating a partial substitution of Fe and Al atoms in Ag matrix. Transmission electron diffraction (TEM) patterns show a number of Ag rings. Both XRD and TEM studies did not reveal any diffraction peaks due to Fe or Al. The average particle size determined from the TEM micrograph is 5.9 nm. This value is in good agreement with the grain size determined from the XRD patterns for the Al substituted samples. The MR was found to increase for smaller Al concentration and it decreases with further increase in Al content. In the samples investigated magnetoresistance ratio reaches a maximum value of about 4.5% for the Fe27 Ag63Al10 film.

Magnetic and Transport Properties Ru1 - xSbxSr2(Sm0.7Ce0.3)2Cu2O10 - δ Compounds

2003 ◽  
Vol 17 (13) ◽  
pp. 2539-2544 ◽  
Author(s):  
T. R. Yang ◽  
V. Toma ◽  
O. Furdui ◽  
G. Ilonca
Keyword(s):  
Magnetic Order ◽  
Solid State Reaction Method ◽  
Partial Substitution ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
Conventional Solid State Reaction ◽  
Reaction Method ◽  
X Ray ◽  
Sb Doping ◽  
Hole Localization

We have investigated the effect of the partial substitution of Sb for Ru in Ru 1 - x Sb x Sr 2( Sm 0.7 Ce 0.3)2 Cu 2 O 10 - δ, (Ru:1222) prepared by conventional solid state reaction method, using X-ray diffraction analysis, electrical resistivity and DC-magnetic susceptibility measurements. Sb doping reduces the conductivity of the system and the onset superconducting transition temperature decreases from 42 K for x = 0 to 21 K for x = 0.06. This maybe due to a distortion of RuO6 octahedral, which is responsible of the increase in hole localization. The corresponding magnetic moment in the investigated samples is about 0.1 μB for Ru. Furthermore we discuss the influence of phase composition on superconducting and magnetic order.

scholarly journals Superconductivity in LiGa2Ir Heusler type compound with VEC = 16

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Karolina Górnicka ◽  
Gabriel Kuderowicz ◽  
Michał J. Winiarski ◽  
Bartłomiej Wiendlocha ◽  
Tomasz Klimczuk
Keyword(s):  
Heat Capacity ◽  
Solid State Reaction Method ◽  
Lattice Parameter ◽  
Coupling Constant ◽  
X Ray Diffraction ◽  
Electron Phonon Interaction ◽  
Type Ii Superconductor ◽  
Electron Phonon Coupling ◽  
A Minor ◽  
Type Crystal

AbstractPolycrystalline LiGa2Ir has been prepared by a solid state reaction method. A Rietveld refinement of powder x-ray diffraction data confirms a previously reported Heusler-type crystal structure (space group Fm-3m, No. 225) with lattice parameter a = 6.0322(1) Å. The normal and superconducting state properties were studied by magnetic susceptibility, heat capacity, and electrical resistivity techniques. A bulk superconductivity with Tc = 2.94 K was confirmed by detailed heat capacity studies. The measurements indicate that LiGa2Ir is a weak-coupling type-II superconductor ($${\uplambda }$$ λ e–p = 0.57, $${\Delta }$$ Δ C/$${\upgamma }$$ γ Tc = 1.4). Electronic structure, lattice dynamics, and the electron–phonon interaction are studied from first principles calculations. Ir and two Ga atoms equally contribute to the Fermi surface with a minor contribution from Li. The phonon spectrum contains separated high frequency Li modes, which are seen clearly as an Einstein-like contribution in the specific heat. The calculated electron–phonon coupling constant $${\uplambda }$$ λ e–p = 0.68 confirms the electron–phonon mechanism for the superconductivity. LiGa2Ir and recently reported isoelectronic LiGa2Rh are the only two known representatives of the Heusler superconductors with the valence electron count VEC = 16.

FERMI SURFACES OF ORGANIC SUPERCONDUCTORS

1993 ◽  
Vol 07 (15) ◽  
pp. 2707-2741 ◽  
Author(s):  
J. WOSNITZA
Keyword(s):  
Organic Superconductors ◽  
Spin Splitting ◽  
Quantum Limit ◽  
Superconducting Transition ◽  
Coupling Constant ◽  
Fermi Surfaces ◽  
Electron Phonon Coupling ◽  
Charge Transfer Salts ◽  
Almost All ◽  
Observable Spin

In this review an overview of the present-day knowledge of the Fermi surfaces of organic superconductors obtained by Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) experiments is given. Almost all measurements reported here were made on charge transfer salts of the type (ET)2X where ET stands for bis(ethelenedithio)-tetrathiafulvalene (or BEDT-TTF) and X is a monovalent anion. The ET-salts are characterized by their extremely two-dimensional properties. Some unique features resulting from this two-dimensionality, like gigantic SdH and dHvA oscillations, directly observable spin-splitting far from the quantum limit and a distinctive angular dependence of the dHvA amplitude will be discussed in detail. By comparison of the measured cyclotron effective mass with the bare band mass the electron-phonon coupling constant can be extracted and the validity of the BCS formula for the superconducting transition temperature can be checked.

H Implantation Improves Superconductivity in Non-Transition Metals

1983 ◽  
Vol 27 ◽  
Author(s):  
F. Ochmann ◽  
B. Stritzker
Keyword(s):  
Transition Temperature ◽  
Transition Metals ◽  
Superconducting Transition Temperature ◽  
Radiation Effects ◽  
Superconducting Transition ◽  
Coupling Constant ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Host Metal

ABSTRACTThe superconducting transition temperature, Tc, of a series of non-transition metals was improved by implantation of H and D into these metals kept below 10 K. In all cases the increase of Tc was considerably larger for H and D implantation with respect of He implantation causing only radiation effects. It could be shown that the enhancement of Tc depends on the electron-phonon coupling constant of the host metal, suggesting that mainly phonon effects dominate the improvement of Tc.

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