Al substitution in MgB2 crystals: influence on superconducting and structural properties

Abstract

Single crystals of Mg1-xAlxB2 have been grown at a pressure of 30 kbar using the cubic anvil technique. Precipitation free crystals with x < 0.1 were obtained as a result of optimization of already developed MgB2 crystal growth procedure. Systematic decrease of the c-axis lattice constant with increasing Al content, when the a-axis lattice constant is practically unchanged, was observed. Variation of the critical temperature on Al content in Mg1-xAlxB2 crystals was found to be slightly different than that one observed for polycrystalline samples since, even a very small substitution of 1-2% of Al leads to the decrease of Tc by about 2-3 K. X-ray and high resolution transmission electron microscopy investigations indicate on the appearance of second precipitation phase in the crystals with x > 0.1. This is in a form of non-superconducting MgAlB4 domains in the structure of superconducting Mg1-xAlxB2 matrix. Resistivity and magnetic investigations show the slight increase of the upper critical field, Hc2, for H//c for the samples with small x, significant reduction of the Hc2 anisotropy at lower temperatures, and decrease of the residual resistance ratio value for Al substituted samples as compared to those of unsubstituted crystals. Superconducting gaps variation as a function of Al content, investigated with point contact spectroscopy for the series of the crystals with Tc in the range from 20 to 37 K, does not indicate on the merging of the gaps with decreasing Tc down to 20 K. It may be related to an appearance of the precipitation phase in the Mg1-xAlxB2 structure.

PDF only, 33 pages, 4 tables, 18 figures

References in corpus (29)

• Beyond Eliashberg superconductivity in MgB2: anharmonicity, two-phonon scattering, and multiple gaps
• Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors
• Evidence for two superconducting energy gaps in MgB2 by point-contact spectroscopy
• Two-Band Superconductivity in MgB2
• Multiband model for tunneling in MgB2 junctions
• Temperature and field dependence of the anisotropy of MgB2
• Vortex Imaging in the pi-Band of Magnesium Diboride
• Direct evidence for two-band superconductivity in MgB_2 single crystals from directional point-contact spectroscopy in magnetic fields
• Carbon substitution in MgB2 single crystals: structural and superconducting properties
• Anisotropy of the Upper Critical Field and Critical Current in Single Crystal MgB${}_2$
• Carbon-substitution effect on the electronic properties of MgB${}_2$ single crystals
• Anisotropic superconducting properties of MgB2 single crystals probed by in-plane electrical transport measurements
• Fermi surface topology and the upper critical field in two-band superconductors - application to MgB2
• Superconducting Transition and Phase Diagram of Single Crystal MgB2
• MgB2 single crystals: high pressure growth and anisotropic properties
• Toward one-band superconductivity in MgB2
• Two-band Eliashberg equations and the experimental Tc of the diboride Mg1-xAlxB2
• The Tc amplification by quantum interference effects in diborides
• Enhancement of the irreversibility field by carbon substitution in single crystal MgB${}_2$
• Single crystal growth of MgB2 and thermodynamics of Mg-B-N system at high pressure
• Temperature-dependent $H_{c2}$ anisotropy in MgB${}_2$ as inferred from measurements on polycrystals
• The structure of the superconducting gap in MgB2 from point-contact spectroscopy
• The Magnetic-field Dependence of the Gaps in a Two-band Superconductor: A Point-contact Study of MgB_2 Single Crystals
• The complex superstructure in Mg1-xAlxB2 at x~0.5
• Crystal structure of the Mg${}_{1-x}$Al${}_x$B${}_2$ superconductors near x=0.5
• Point-contact spectroscopy in MgB2 single crystals in magnetic field
• Superconducting energy gap distribution in c-axis oriented MgB${}_2$ thin film from point contact study
• Influence of Fermi surface topology on the quasiparticle spectrum in the vortex state
• MgB2 and Mg1-xAlxB2 single crystals: high-pressure growth and physical properties

Cited by in corpus (34)

• Effects of neutron irradiation on polycrystalline Mg11B2
• Observation of the Crossover from Two-Gap to Single-Gap Superconductivity through Specific Heat Measurements in Neutron Irradiated MgB2
• Large decrease in the critical temperature of superconducting LaFeAsO0.85 compounds doped with 3% atomic weight of nonmagnetic Zn impurities
• Strong magnetic pair breaking in Mn substituted MgB_2 single crystals
• Superconducting and Normal State Properties of Neutron Irradiated MgB2
• Break-junction technique in application to layered superconductors (Review article)
• Superconductivity of magnesium diboride
• Point-contact spectroscopy of Al- and C-doped MgB2. Superconducting energy gaps and scattering studies
• MgB2 single crystals substituted with Li and with Li-C: Structural and superconducting properties
• Point-contact spectroscopy in neutron-irradiated Mg^{11}B_2
• Isotope effect on the E2g phonon and mesoscopic phase separation near the electronic topological transition in Mg1-xAlxB2
• Role of charge doping and lattice distortions in codoped Mg_{1-x}(AlLi)_{x}B_2 compounds
• Electron-phonon coupling and two-band superconductivity of Al- and C-doped MgB2
• Point-contact Andreev-reflection spectroscopy in segregation-free Mg_{1-x}Al_{x}B_2 single crystals up to x=0.32
• Role of interband scattering in neutron irradiated MgB${}_2$ thin films by Scanning Tunneling Spectroscopy measurements
• Infrared properties of Mg${}_{1-x}$Al${}_x($B${}_{1-y}$C${}_y$)${}_2$ single crystals in the normal and superconducting state
• Temperature Dependence of Superconducting Gaps in Mg(Al)B2 System Investigated by SnS-Andreev Spectroscopy
• de Haas-van Alphen effect investigation of the electronic structure of Al substituted MgB_2
• Thermal conductivity of Al-doped MgB2: Impurity scattering and the validity of the Wiedemann-Franz law
• Local Tunneling Study of Three-Dimensional Order Parameter in the $\pi$-band of Al-doped MgB${}_2$ Single Crystals
• de Haas-van Alphen effect investigations of the electronic structure of pure and aluminum-doped MgB_2
• Mn and Fe Impurities in MgB_{2}
• Ab-initio investigation of the covalent bond energies in the metallic covalent superconductor MgB2 and in AlB2
• Ab initio modeling of superconducting alloys
• A model for critical current effects in point-contact Andreev-reflection spectroscopy
• Effect of site dilution in the two-dimensional attractive Hubbard model
• High-pressure high-temperature solution growth, structural, and superconducting properties of Fe-substituted MgB2 single crystals
• Influence of the carbon substitution on the critical current density and AC losses in MgB2 single crystals
• Effect of doping on irreversible Campbell length in MgB${}_2$ single crystals
• Is Delta_{pi}-gap-only superconductivity possible in Mg_{1-x}Al_{x}B_{2} and Mg(B_{1-y}C_{y})_{2} alloys?
• Electron-phonon coupling and superconductivity in $\alpha$-MoB${}_2$ as a function of pressure
• Influence of carbon on intraband scattering in Mg(B1-xCx)2
• Discovery of a new magnesium iron boride Mg4Fe1.1B13.9 in the Mg-Fe-B-N system
• Gap fluctuations, Cooper pairs with finite center-of-mass momentum, and suppression of superconductivity in inhomogeneous systems with dopant superpuddles agglomerates