Bulk High-Entropy Hexaborides

TL;DR

This paper reports the successful fabrication and characterization of dense bulk high-entropy hexaborides with promising mechanical and electronic properties, marking a novel development in high-entropy ceramic materials.

Contribution

First synthesis and detailed characterization of dense bulk CaB6-typed high-entropy hexaborides with homogeneous composition and enhanced properties.

Findings

Achieved >98.5% density in bulk hexaborides

Measured microhardness of 16-18 GPa

Determined work functions of 3.7-4.0 eV

Abstract

For the first time, a group of CaB6-typed cubic rare earth high-entropy hexaborides have been successfully fabricated into dense bulk pellets (>98.5% in relative densities). The specimens are prepared from elemental precursors via in-situ metal-boron reactive spark plasma sintering. The sintered bulk pellets are determined to be single-phase without any detectable oxides or other secondary phases. The homogenous elemental distributions have been confirmed at both microscale and nanoscale. The Vickers microhardness are measured to be 16-18 GPa at a standard indentation load of 9.8 N. The nanoindentation hardness and Young's moduli have been measured to be 19-22 GPa and 190-250 GPa, respectively, by nanoindentation test using a maximum load of 500 mN. The material work functions are determined to be 3.7-4.0 eV by ultraviolet photoelectron spectroscopy characterizations, which are significantly higher than that of LaB6.