Modulated crystal structure of the atypical charge density wave state of single-crystal Lu2Ir3Si5

The three-dimensional charge density wave (CDW) compound ${\mathrm{Lu}}₂{\mathrm{Ir}}₃{\mathrm{Si}}₅$ undergoes a first-order CDW phase transition at around 200 K. An atypical CDW state is found, that is characterized by an incommensurate CDW with $\mathbf{q}=[0.2499(3),0.4843(4),0.2386(2)]$ at 60 K, and a large orthorhombic-to-triclinic lattice distortion with $\ensuremath{\beta}=91.945{(2)}^{\ensuremath{\circ}}$. We present the modulated crystal structure of the incommensurate CDW state. Structural analysis shows that the CDW resides on the zigzag chains of iridium atoms along $\mathbf{c}$. The structural distortions are completely similar between nonmagnetic ${\mathrm{Lu}}₂{\mathrm{Ir}}₃{\mathrm{Si}}₅$ and previously studied isostructural magnetic ${\mathrm{Er}}₂{\mathrm{Ir}}₃{\mathrm{Si}}₅$ with the small differences explained by the different values of the atomic radii of Lu and Er. Such a similarity is unique to ${R}₂{\mathrm{Ir}}₃{\mathrm{Si}}₅$ $(R=\mathrm{rare}\phantom{\rule{0.28em}{0ex}}\mathrm{earth})$. It differs from, for example, the rare-earth CDW compounds ${R}₅{\mathrm{Ir}}₄{\mathrm{Si}}₁₀$ for which ${\mathrm{Lu}}₅{\mathrm{Ir}}₄{\mathrm{Si}}₁₀$ and ${\mathrm{Er}}₅{\mathrm{Ir}}₄{\mathrm{Si}}₁₀$ possess entirely different CDW states. We argue that the mechanism of CDW formation, thus, is different for ${R}₂{\mathrm{Ir}}₃{\mathrm{Si}}₅$ and ${R}₅{\mathrm{Ir}}₄{\mathrm{Si}}₁₀$.