Disordered La3Cu4.88Se7

The crystal structure of copper(I) lanthanum selenide, La₃Cu_4.88Se₇, obtained from the La₂Se₃–Cu₂Se quasi‐binary system, has been investigated using X‐ray single‐crystal diffraction. The positions of the La and Se atoms are ordered and lie on mirror planes, whereas all positions for the Cu atoms are partially occupied. The crystal is built from edge‐sharing [LaSe₆] and [LaSe₇] polyhedra. The five positions for the Cu atoms determine an ionic diffusion pathway in the structure.