Comparison of crystal structure and microstructure between monoclinic and cubic Cu₂SnSe₃. (a) XRD patterns of Cu₂Sn_1−xCd_xSe₃ (x varies from 0 to 0.15). The right panel shows an enlarged view of the main Bragg peak at 27°. (b) Lattice parameters as a function of x. (c), (d) Atomic-resolution HAADF images of pristine Cu₂SnSe₃. Corresponding SAD pattern taken along the [103] zone axis in (c); lattice model of the monoclinic structure in (d); atomic positions and distribution in (e). (f), (g) Atomic-resolution HAADF images of Cu₂Sn_0.9Cd_0.1Se₃. Corresponding SAD pattern taken along the [101] zone axis in (f); lattice model of the cubic structure in (g); atomic positions and distribution in (h).