Vacancy ordering induced topological electronic transition in bulk Eu ₂ ZnSb ₂

Abstract

Metal-semiconductor transitions from changes in edge chirality from zigzag to armchair were observed in many nanoribbon materials, especially those based on honeycomb lattices. Here, this is generalized to bulk complex Zintl semiconductors, exemplified by Eu2ZnSb2 where the Zn vacancy ordering plays an essential role. Five Eu2ZnSb2 structural models are proposed to guide transmission electron microscopy imaging. Zigzag vacancy ordering models show clear metallicity, while the armchair models are semiconducting with indirect bandgaps that monotonously increase with the relative distances between neighboring ZnSb2 chains. Topological electronic structure changes based on cation ordering in a Zintl compound point toward tunable and possibly switchable topological behavior, since cations in these are often mobile. Thus, their orderings can often be adjusted by temperature, minor alloying, and other approaches. We explain the electronic structure of an interesting thermoelectric and point the way to previously unidentified types of topological electronic transitions in Zintl compounds.

Large Gap Topological Insulating Phase and Anisotropic Rashba and Chiral Spin Textures in Monolayer Zintl A2MX2

“…Very recently, this has been further demonstrated that these materials host nontrivial topological phases . For instance, by changing the cation ordering in Zintl phase bulk Eu 2 ZnSb 2 , a topological transition was observed, demonstrating its tunabilty …”

“…44 Very recently, this has been further demonstrated that these materials host nontrivial topological phases. 45 For instance, by changing the cation ordering in Zintl phase bulk Eu 2 ZnSb 2 , a topological transition was observed, demonstrating its tunabilty. 45 Although numerous studies have already been devoted to Zintl phase compounds, especially in the field of thermoelectric materials, 43,46,47 studies on the topological properties of monolayer Zintl phase A 2 MX 2 have yet to be fully explored.…”

“…45 For instance, by changing the cation ordering in Zintl phase bulk Eu 2 ZnSb 2 , a topological transition was observed, demonstrating its tunabilty. 45 Although numerous studies have already been devoted to Zintl phase compounds, especially in the field of thermoelectric materials, 43,46,47 studies on the topological properties of monolayer Zintl phase A 2 MX 2 have yet to be fully explored. Also, due to their intrinsic complex structures and varying structure terminations when cleaved, breaking of symmetry emerges, and interesting spin properties can be observed.…”

“…Surprisingly, it was found that some TE materials with a narrow bandgap may exhibit topological properties because of the presence of a strong spin–orbit coupling (SOC) effect . Very recently, this has been further demonstrated that these materials host nontrivial topological phases . For instance, by changing the cation ordering in Zintl phase bulk Eu 2 ZnSb 2 , a topological transition was observed, demonstrating its tunabilty …”

Local order in a disordered Zintl phase boosts its thermoelectric performance

“…They found that locally ordered zinc atoms retain the material’s high electronic conductivity, while long-range disorder keeps the thermal conductivity low. “We knew that the key feature of Eu 2 ZnSb 2 is a crystal structure that has a Zn-site with a 50% occupancy 3 ,” says Zhang, “but the exact crystal model is actually unknown so the high degree of local order was an unexpected find.”…”