Synthesis of equimolar solid solution of zirconium and hafnium diborides by vacuum-thermal routes

We explored the Zr₁₋ₓHfₓB₂ system with first-principles cluster expansion and thermodynamic analysis of possible reactions targeting the synthesis in vacuum-thermal conditions. The results suggest that the system may have a slight tendency to ordering but at high temperatures the formation of solid solutions is driven by the entropy of mixing. We realized the synthesis of an equimolar composition (x = 0.5) by sintering of ZrB2 and HfB2 and reduction from oxides by boron with varying homogenization of the reacting mixtures. The temperature of the complete transformation strongly depended on the reactants homogeneity and was 1900 °C for more coarse raw materials and below 1700 °C for a fine hydrothermal mixture of oxides. The possibility of producing non-equimolar compositions of the solid solutions by the same method was also experimentally demonstrated.