Mixing the transition metals in transition metal diborides

In this study, the phase behavior of the mixed transition metal diborides is explored and the thermodynamic stability of the equiatomic mixed diborides, also known as the high entropy diborides (HEBs) is investigated by employing the density functional theory (DFT), the quasi-harmonic approximation (QHA), and the calculation-of-the-phase-diagram (CALPHAD) approach. The findings reveal insights into the roles of mixing enthalpy, vibrational entropy and configurational entropy in determining the phase stability of the mixed diborides, paving the ways for the materials design of the mixed diborides beyond the equiatomic compounds. In addition, the detailed discussion of the limitations in the Debye-Grüneisen model for transition metal diborides provides the understanding of the phonon contribution to the thermodynamic stability.