Strain-Induced Topological Phase Transitions Covering the Z4 Indicator in Orthorhombic Li2AuBi

The Z 4 symmetry indicator is widely used to classify topological materials hosting inversion symmetry. We find orthorhombic Li2AuBi in space group Cmcm is a topological insulator with Z 4 = 1 under no strain via first-principles calculations. Due to small band gaps in the kz = 0 plane, the band inversions can be selectively induced by moderate external strains to realize phases covering all values of Z 4 = 1, 2, 3, and 0. Detailed Z 4 phase diagrams are plotted under various moderate strains. The (001) surface states and their associated Fermi surfaces and spin textures are calculated. The topological surface states have different connectivities and different spin textures for the four different Z 4 phases. The tunability of topological surface states via moderate strain suggests Li2AuBi as an attractive topological material for device applications.

Polyanionic Gold-Tin Bonding and Crystal Structure Preference in REAu1.5Sn0.5 (RE = La, Ce, Pr, Nd)

During a systematic search of the RE-Au-Sn (RE = La, Ce, Pr, Nd) ternary phase space, a series of compounds with the general formula REAu_1.5Sn_0.5 have been identified. These phases can be synthesized by arc melting the elemental metals, followed by annealing. The crystal structures were solved using single-crystal X-ray diffraction, with the composition confirmed by energy-dispersive X-ray spectroscopy. All four compounds crystallize in orthorhombic space group Imma with the CeCu₂-type structure. Most notable in these compounds is the polyanionic backbone composed of a single statistically mixed Au/Sn position, which creates a puckered hexagonal bonding network separated by the rare-earth atoms. Electronic structure calculations indicate that the Au 5d bands are dominant in the density of states, while the crystal orbital Hamilton population (-COHP) curves demonstrate Au-Au and Au-Sn interactions, which stabilize the crystal structure. Likewise, a qualitative electron localization function analysis supports the existence of a polyanionic network, and a Bader charge analysis implies anionic character on Au and Sn. The preference for these compounds to adopt the simple CeCu₂-type structure is also determined using density functional theory calculations and compared to related compounds to establish a better picture of the unusual behavior of Au in polar intermetallic compounds.

Design and structural characterization of the all-metal aromatic sandwich species [Bi3Au3Bi3]3−: insight from density functional theory

The [Bi₃Au₃Bi₃]³⁻ species, with hollow features, has a unique all-metal sandwich aromatic structure.