Synthesis of high‐purity high‐entropy metal diboride powders is critical to implementing their extensive applications. However, the related studies are rarely reported. Herein we first theoretically studied the synthesis possibility of high‐purity high‐entropy diboride powders, namely (Hf0.25Ta0.25Nb0.25Ti0.25)B2 (HTNTB), via boro/carbothermal reduction by analyzing the thermodynamics of the possible chemical reactions and then successfully synthesized the high‐purity and superfine HTNTB powders via boro/carbothermal reduction for the first time. The as‐prepared powders exhibited low‐oxygen impurity content of 0.49 wt% and small average particle size of 260 nm. Meanwhile, they possessed good single‐crystal hexagonal structure of metal diborides and high‐compositional uniformity from nanoscale to microscale. This work will open up a new research field on the synthesis of high‐purity high‐entropy metal diboride powders.

Synthesis of the powders is critical for achieving the extensive applications of high‐entropy carbides (HECs). Previously reported studies focus mainly on the high‐temperature (>2000 K) synthesis of HEC micro/submicropowder, while the low‐temperature synthesis of HEC nanopowders is rarely studied. Herein we reported the low‐temperature synthesis of HEC nanopowders, namely (Ta0.25Nb0.25Ti0.25V0.25)C (HEC‐1), via molten salt synthesis for the first time. The synthesis possibility of HEC‐1 nanopowders was first theoretically demonstrated by analyzing lattice size difference and chemical reaction thermodynamics based on the first‐principle calculations, and then the angular HEC‐1 nanopowders were successfully synthesized via molten salt synthesis at 1573 K. The as‐synthesized nanopowders possessed the single‐crystal rock‐salt structure of metal carbides and high compositional uniformity from nanoscale to microscale. In addition, their formation mechanism was well interpreted by a classical molten salt‐assisted growth.

The synthesis of high‐entropy metal carbide powders is critical for implementing their extensive applications. However, the one‐step synthesis of high‐entropy metal carbide powders is rarely studied. Herein, the synthesis possibility of high‐entropy metal carbide powders, namely (Zr0.25Ta0.25Nb0.25Ti0.25)C (ZTNTC), via one‐step carbothermal reduction was first investigated theoretically by analyzing chemical thermodynamics and lattice size difference based on the first‐principle calculations, and then the ZTNTC powders with particle size of 0.5‐2 μm were successfully synthesized experimentally. The as‐synthesized powders not only had a single rock‐salt crystal structure of metal carbides, but also possessed high‐compositional uniformity from nanoscale to microscale. More interestingly, they exhibited the distinguished coral‐like morphology with the hexagonal step surface, whose growth was governed by a classical screw dislocation growth mechanism.

High-entropy nanomaterials have been arousing considerable interest in recent years due to their huge composition space, unique microstructure, and adjustable properties. Previous studies focused mainly on high-entropy nanoparticles, while other high-entropy nanomaterials were rarely reported. Herein, we reported a new class of high-entropy nanomaterials, namely (Ta0.2Nb0.2Ti0.2W02Mo0.2)B2 high-entropy diboride (HEB-1) nanoflowers, for the first time. The formation possibility of HEB-1 was first theoretically analyzed from two aspects of lattice size difference and chemical reaction thermodynamics. We then successfully synthesized HEB-1 nanoflowers by a facile molten salt synthesis method at 1473 K. The as-synthesized HEB-1 nanoflowers showed an interesting chrysanthemum-like morphology assembled from numerous well-aligned nanorods with the diameters of 20-30 nm and lengths of 100-200 nm. Meanwhile, these nanorods possessed a single-crystalline hexagonal structure of metal diborides and highly compositional uniformity from nanoscale to microscale. In addition, the formation of the as-synthesized HEB-1 nanoflowers could be well interpreted by a classical surface-controlled crystal growth theory. This work not only enriches the categories of high-entropy nanomaterials but also opens up a new research field on the high-entropy diboride nanomaterials.

The synthesis of the multi-component transition-metal diboride (MeB 2 ) solid-solution powders has been recently attracting considerable attentions. However, the synthesis of the ternary or more component MeB 2 solid-solution powders has rarely been reported until now. To fabricate the ternary MeB 2 solid-solution powders, herein we utilized two kinds of the ternary MeB 2 solid solutions as prototypes, namely (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 singlecrystal 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. K E Y W O R D Sfirst-principles calculations, molten salt synthesis, nanorods, solid-solution powders, transition-metal diborides