Cu[Li_1/3Sn_2/3]O₂ and Cu[Na_1/3Sn_2/3]O₂: Crystal Structure and Phonon Dispersion in Quaternary Honeycomb Delafossites

Magnetic materials with spin-1/2 ions on a two dimensional honeycomb lattice are candidates for a Kitaev spin liquid phase. The study of non-magnetic honeycomb delafossites provides a basis to model the physical properties of magnetic honeycomb materials. Here, we report two new quaternary non-magnetic delafossites, Cu[Li_1/3Sn_2/3]O₂ and Cu[Na_1/3Sn_2/3]O₂, with honeycomb ordering synthesized via a topotactic cation-exchange reaction. The monoclinic C2/c space group and twinned stacking faults are determined from the Rietveld refinement and TEM analysis. Additionally, the phonon heat capacity for these non-magnetic layered oxides is captured accurately by first principles calculations. These results are an important step toward having a reliable model to calculate phonon contribution to the heat capacity in magnetic delafossites¹.

[1] Inorganic Chemistry 57, 12709 (2018).