Modeling of the Phase Evolution in Mg1-xAlxB2 (0 < x < 0.5) and Its Experimental Signatures.

Despite the chemical and structural simplicity of MgB2, at 39 K this compound has the highest known superconducting transition temperature (Tc) of any binary compound. Electron doping by substituting Al for Mg leads to decreasing Tc, and the observed concentration dependent rate of decrease has been proposed to arise from the nonideal character of MgB2−AlB2 solid solutions, which derives from the existence of an ordered Mg0.5Al0.5B2 compound. Heterogeneous nanoscale structure patterns in solid solutions have emerged as an important concept for complex materials, ranging from actinide alloys and oxides to high-temperature cuprate superconductors and manganite-based materials exhibiting colossal magnetoresistivity. In this work we investigate the formation of structural heterogeneities in Mg1−xAlxB2, which take the form of nanoscale Al−Al and Al−Mg domains of different geometries and sizes, using molecular statics and Monte Carlo simulations, and in particular we study the corresponding signatures in diffra...