Spark plasma sintering and characterization of bulk La1-xSrxB6 hexaborides

Herein, bulk La1-xSrxB6 hexaborides with >96.5% in relative densities have been fabricated by SPS, and the phase composition, microstructure, mechanical and thermionic emission properties are investigated. The sintered specimens with average grain sizes of about 14 & mu;m are determined to be CsCl-type single-phase solid solutions without any detectable impurities or other secondary phases. The homogenous elemental distributions of La and Sr have been confirmed at both microscale and nanoscale. The Vickers hardness (18-23 GPa) of these sintered specimens are higher than LaB6, while the indentation fracture toughness (about 2.00 MPa m1/2) are comparable to LaB6. The nanoindentation hardness and Young's moduli have been measured to be 26-30 GPa and 380-400 GPa, respectively, by nanoindentation tests at a maximum load of 20 mN. Only from the perspective of work function, bulk La1-xSrxB6 hexaborides with lower work functions and higher thermionic emission current den-sities than LaB6 have a potential to be a class of excellent hot cathodes.

Automated summary

Bulk La1-xSrxB6 hexaborides with high relative densities were fabricated using SPS and their phase composition, microstructure, mechanical and thermionic emission properties were investigated. The sintered specimens were found to be CsCl-type single-phase solid solutions without impurities or secondary phases. Homogenous elemental distributions of La and Sr were confirmed at both microscale and nanoscale. The sintered specimens exhibited higher Vickers hardness and comparable indentation fracture toughness compared to LaB6. Nanoindentation tests revealed high nanoindentation hardness and Young's moduli for the specimens. In terms of work function, bulk La1-xSrxB6 hexaborides showed lower work functions and higher thermionic emission current densities than LaB6, making them a potential class of excellent hot cathodes.