The structural diversity and applications of intermetallic germanides make them interesting candidates for exploration. Past the ages of binary and ternary compound explorations, quaternary structures have gained more attention. Counterintuitively, more components do not directly translate into more compounds in a given system. Often, quaternary phases are thermodynamic competitors, e.g., Tb4RhInGe4-type vs Ho4Ni2InGe4-type, which prior to this work, were never observed in the same system. In this work, we expand the quaternary germanide series RE4IrInGe4 (RE = Y, Ce-Nd, Sm, Gd, Ho-Er) synthesized via arc-melting followed by annealing. To explore the bonding trends, electronic structure calculations were performed for Ce4IrInGe4 and Ce4Ir2InGe4, which crystallize in Tb4RhInGe4- and Ho4Ni2InGe4-types, respectively. Along with the obvious Ir-Ge bonding contribution, Ce-Ge bonding turned out to be one of the most important interactions that govern the structure formation and explain the RE series limits. To separate the Tb4RhInGe4-type from the closely related Ho4Ni2InGe4-type, a structure map was developed by using the PLS-DA technique. In the PLS-DA loadings, the radii of the elements and valence electron counts made the top contributions to the classification of these two types. Further, to understand the structural evolution, we analyzed the germanides using materials informatics tools and proposed a mechanism using their coordination environments.
Ponomarev et al. (Tue,) studied this question.