Role of charge doping and lattice distortions in codopedMg1−x(AlLi)xB2<

Abstract

We prepared a series of Mg 1−x ͑AlLi͒ x B 2 samples with 0 ഛ x ഛ 0.45 in order to compensate with Li the electron doping induced by Al. Structural characterization by means of neutron and x-ray diffraction confirms that Li enters the MgB 2 structure even though in an amount less than nominal one. We performed susceptibility, resistivity, and specific heat measurements. Vibrational properties were also investigated by means of Raman spectroscopy. We compare these results with those obtained on a homologous series of Mg 1−x Al x B 2 samples. The systematic success of scaling the relevant properties with the Al content rather than with the electron doping suggests that lattice deformation plays an important role in tuning the superconducting properties.

Structural and Superconducting Property Variations with Nominal Mg Non‐Stoichiometry in MgxB2 and Its Enhancement of Upper Critical Field

“…[27,28] It is apparent from Figure 6 that with decreasing x, the 730 cm -1 peak increases in intensity relative to the 600 cm -1 peak. A compilation of various property measurements is shown in Figure 7 and this allows a general picture of the relation of stoichiometry to properties to emerge.…”

“…These features have been observed in Al-doped samples and have been associated with structural disorder. [27][28][29] The appearance of more than one phonon peak further implies the violation of Raman selection rules induced by disorder resulting in a modified …”

Effects of neutron irradiation on polycrystallineMg11B2

“…Moreover, disorder introduced by doping might enhance interband scattering, also as an effect of structural deformations, and does not allow us to carefully identify the real reasons for the changes in the superconducting properties. These problems can be overcome either by co-doping, as attempted with a substitution of lithium and aluminium on Mg sites by Monni et al 12 that, nevertheless, did not obtain a complete charge balance, or by particles irradiation.…”

MgB2single crystals substituted with Li and with Li-C: Structural and superconducting properties

“…Due to the anisotropic character of MgB 2 , single crystal studies provide a more detailed insight and such studies have been reported for C, Al, and Mn substitutions. [18][19][20][21][22][23] Other substitutions, such as Li 24,25 and co-substitutions with Al and Li 26,27 were investigated on polycrystalline samples or polycrystalline thin films.…”