Structural, magnetic, and thermionic emission properties of multi-functional La1-xCaxB6 hexaboride.

Herein, we report the synthesis of nanocrystalline La 1-x Ca x B 6 (0 ≤ x ≤ 1) hexaboride powders by solid-state reaction and their subsequent consolidation via spark plasma sintering. The structural, magnetic and thermionic emission properties of La 1-x Ca x B 6 hexaboride are investigated. All of the synthesized nanocrystalline hexaboride powders are single phase with the CsCl -type structure and no ferromagnetic impurity phases have been detected from X-ray diffraction. Magnetic measurements show that weak ferromagnetism at room temperature is found in nanocrystalline La 1-x Ca x B 6 hexaboride powders, and the magnetism was attributed to the presence of the intrinsic defects, based on the data of the HRTEM. Thermionic emission measurements indicate that the maximum emission intensity for bulk La 0.4 Ca 0.6 B 6 at 1873 K reached 20.02 A/cm 2 , which is more than three times higher as compared to bulk CaB 6 (∼6.04 A/cm 2 ). When the La doping was increased to 40 at%, the work function of CaB 6 decreased from 2.95 to 2.76 eV, indicating an improvement in the thermionic emission performance. Therefore, the quasibinary La 1-x Ca x B 6 hexaboride may have an application as a promising cathode. [ABSTRACT FROM AUTHOR]