Structural Evolution from Hyper-Honeycomb to Honeycomb Networks and Superconductivity in LaPt${}_x$Si${}_{2-x}$

We report the crystal structures and superconductivity (SC) of LaPt${}_x$Si${}_{2-x}$ ($0.5\le x\le 1.0$) that are solid solutions of LaSi${}_2$ and LaPtSi with centrosymmetric tetragonal ($I{4}_1\mathrm{/}amd$, $D_{4h}^{19}$, #141) and non-centrosymmetric tetragonal ($I{4}_{1}md$, $C_{4v}^{11}$, #109) structures, respectively. It was found that at $0.86\le x\le 1.00$, the non-centrosymmetric tetragonal symmetry is preserved, while partial disorder appears in alternating Pt and Si of the hyper-honeycomb network. The superconducting transition temperature $T_{\mathrm{c}}$ was drastically reduced from 3.9 K to 1.5 K as $x$ varies from 1.0 to 0.86. Additionally, a hexagonal phase with an AlB${}_2$-type structure ($P6\mathrm{/}mmm$, $D_{6h}^1$, #191) has been discovered at $0.50\le x\le 0.71$ with a honeycomb network of statistically distributed Pt and Si atoms. The hexagonal phase exhibited SC at $T_{\mathrm{c}}=0.38$ K. This system provides an opportunity to investigate the relationship between topological electronic states, SC, and disorders