Synthesis and characterization of the ternary metal diboride solid-solution nanopowders

The synthesis of the multi-component transition-metal diboride (MeB2) solid-solution powders has been recently attracting considerable attentions. However, the synthesis of the ternary or more component MeB2 solid-solution powders has rarely been reported until now. To fabricate the ternary MeB2 solid-solution powders, herein we utilized two kinds of the ternary MeB2 solid solutions as prototypes, namely (Hf1/3Zr1/3Ti1/3)B-2 (HZTB) and (Ta1/3Nb1/3Ti1/3)B-2 (TNTB). The formation possibility of HZTB and TNTB was first analyzed by the first-principles calculations and then we attempted of fabricated them by a simple molten salt synthesis technique. The first-principles calculations results showed that the mixing Gibbs free energy at room temperature and lattice size difference at 0 K of HZTB and TNTB were (1.666 kJ/mol and 3.146%) and (-3.030 kJ/mol and 1.254%), respectively. This suggested that TNTB solid solution was more prone to being fabricated than HZTB solid solution. The experimental results showed the high purity TNTB solid-solution nanopowders were successfully synthesized by the molten salt synthesis technique at 1373 K with 30% excessive B as precursors while the HZTB solid solution was not able to be synthesized by the molten salt synthesis technique. The as-synthesized TNTB solid-solution nanopowders exhibited the distinguished nanorod morphology with the diameters of 20-40 nm and lengths of 100-200 nm. Meanwhile, they possessed the good single-crystal hexagonal structure and high compositional uniformity from nanoscale to microscale. In addition, their formation mechanism associated to the possible chemical reactions was well interpreted by the thermodynamics analysis.