Synthesis and Characterization of the 18-Electron Polar Intermetallics CaAuBi, BaAgBi, and CaAuP

Abstract

The RMX family of ternary 18-electron compounds, in which R is an alkaline earth metal, M is a Group 11 transition metal, and X is a pnictogen, can be expected to host a variety of electronic phenomena of interest. However, many of these compounds remain unstudied from this perspective. In this work, I synthesize the compounds CaAuBi, BaAgBi, and CaAuP, and report the results of their structural and electronic characterization. For CaAuBi, I report the discovery of a structural phase transition under pressure. From this result, predictions for the electronic properties of this compound under pressure are made, and relationships are proposed between chemistry and structure type within the family of RMX compounds. For BaAgBi, I show and investigate the results of band structure calculations, which suggest this compound may be a three-dimensional Dirac semimetal, an exotic electronic state of matter. A new method of crystal growth for this compound is developed, and preliminary transport properties are reported. Evidence towards superconductivity below 3 K in BaAgBi is found, and I discuss the implications of this result on the proposed electronic structure. In samples of CaAuP, a superconducting impurity with T\(_{c}\) \(\approx\)11 K is found, and attempts to identify this phase are detailed. In addition, I report the discovery of the new binary compound Ca\(_{5}\)P\(_{3}\). Altogether, my work on CaAuBi,BaAgBi, and CaAuP suggests that further study of the structural and electronic properties of these and related RMX systems is merited.