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

Herein, we report the synthesis of nanocrystalline La1-xCaxB6 (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 La1-xCaxB6 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 La1-xCaxB6 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 La0.4Ca0.6B6 at 1873 K reached 20.02 A/cm2, which is more than three times higher as compared to bulk CaB6 (∼6.04 A/cm2). When the La doping was increased to 40 at%, the work function of CaB6 decreased from 2.95 to 2.76 eV, indicating an improvement in the thermionic emission performance. Therefore, the quasibinary La1-xCaxB6 hexaboride may have an application as a promising cathode.