Figure 3. XRD patterns of all seven specimens after SPS at 2000 °C, where the peaks of the primary hexagonal phase are indexed.

Six of seven specimens (except for HEB #6) exhibit largely a single hexagonal phase of the AlB₂ structure, albeit the presence of minor secondary (Zr, Hf)O₂ (native oxides), which are represented by the low-intensity peaks that are not indexed here the figure clarity (but indicated by the solid dots in Supplementary Figs S1–S7). As the only special case, a secondary boride phase was observed in HEB #6, with XRD peaks matching those of the (Ti_1.6W_2.4)B₄ compound, while the major XRD peaks still represent a hexagonal metal diboride solid-solution phase.