Cr₃GeN: A Nitride with Orthorhombic Antiperovskite Structure

In contrast to ternary oxides, the number of known ternary nitrides is an order of magnitude lower, which is partially the result of their less exothermic free energy of formation and the resulting lower thermodynamic stability. This challenges experimentalists to continuously explore the synthetic parameter space and push toward new nitride phases. Here, we demonstrate the synthesis of a hitherto unknown orthorhombic structure of Cr3GeN, which typically crystallizes in a tetragonal structure. As derived from density functional theory calculations, formation energies of both phases are similar, and orthorhombic Cr3GeN can be stabilized by choosing lower reaction temperatures. According to detailed thermodynamic analysis, the new compound is stable up to 500 °C and exhibits the same phase transitions as the tetragonal phase at higher temperatures. Magnetic characterization suggests antiferromagnetic order for both polymorphs.