The Synthesis and Characterization of NaCaSb

• Mackenzie Robinson, Chemistry, University of Delaware

• Svilen Bobev, Chemistry, University of Delaware

Topological insulators have become a topic of interest for researchers in the past 20 years due to their unique combination of insulating bulk properties and conductive surface states, a phenomenon driven by spin-orbit coupling (SOC). SOC is enhanced in heavy elements, which leads to Alkali and Alkaline earth metal groups being strong candidates in these systems. The ABX-type topological insulator – where A is an alkali metal, B is an alkaline earth metal, and X is a pnictogen – has been predicted strictly through computational analysis, therefore, experimental verification remains scarce. Additionally, many ABX systems fail to crystallize in the desired 1:1:1 phase. In this study, we synthesized NaCaSb, a new ternary pnictide by direct reaction synthesis in evacuated quartz vessels followed by controlled heating. The crystal structure of NaCaSb was elucidated using powder and single-crystal X-ray diffraction. This data showed evidence of a face-centered cubic space group F -4 3 m (No. 216) with unit cell parameters a =b = c = 7.43930 Å; further confirming the formation of a 1:1:1 ABX-type phase. This work contributes to addressing gaps between theoretical predictions and experimentally synthesized compounds in the scope of topological insulators. Filling in these experimental gaps and expanding the current database of ABX topological insulators would set up important groundwork for applications in quantum computing and thermoelectric technologies.