Role of charge doping and lattice distortions in codoped Mg(1-x)(AlLi)(x)B(2) compounds

We prepared a series of Mg(1-x)(AlLi)(x)B(2) samples with 0 <= x <= 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.