Crystal structure, chemical bonding, and mechanical properties of EuMg2Bi2

EuMg2Bi2, a magnetic topological semimetal, has garnered significant interest for its potential in spintronics, quantum computing, magnetoelectric devices, and thermoelectric energy conversion. However, its temperature-dependent structural evolution, mechanical properties, and bonding characteristics remain unexplored. In this study, we first determine the crystallographic structure of EuMg2Bi2 from 100 to 400 K using high-resolution synchrotron powder and single-crystal X-ray diffraction. The Debye temperature, obtained from isotropic atomic displacement parameters, is 169(4) K, consistent with low-temperature heat capacity data, and structural refinements reveal nearly isotropic lattice expansion. Mechanical property evaluations by theoretical calculations and three-point bending tests confirm the intrinsic brittleness of EuMg2Bi2, as indicated by Pugh's ratio below 1.75 and a maximum fracture strain of only 0.44%. This can be attributed to three types of comparable polar bonds with largely ionic character in the structure as revealed by chemical bonding analysis based on the quantum theory of atoms in molecules, forming a nearly isotropic three-dimensional bonding network that likely suppresses interlayer slip and, thus, contributes to the poor plasticity of this compound.