A theoretical investigation of mixing thermodynamics, age-hardening potential, and electronic structure of ternary M(1)(1–x)M(2)(x)B(2) alloys with AlB(2) type structure

Transition metal diborides are ceramic materials with potential applications as hard protective thin films and electrical contact materials. We investigate the possibility to obtain age hardening through isostructural clustering, including spinodal decomposition, or ordering-induced precipitation in ternary diboride alloys. By means of first-principles mixing thermodynamics calculations, 45 ternary M(1)(1–x)M(2)(x)B(2) alloys comprising M(i)B(2) (M(i) = Mg, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta) with AlB(2) type structure are studied. In particular Al(1–x)Ti(x)B(2) is found to be of interest for coherent isostructural decomposition with a strong driving force for phase separation, while having almost concentration independent a and c lattice parameters. The results are explained by revealing the nature of the electronic structure in these alloys, and in particular, the origin of the pseudogap at E(F) in TiB(2), ZrB(2), and HfB(2).