Copper Bismuth Chalcogenide Halogenides with Extensively Disordered and Mobile Copper(I) Cations

A new family of quaternary phases with the general sum formula Cu_3+δBi_5–δSe_8–2δX_2+2δ (X = Cl, Br) was discovered by slow cooling of high temperature melts. Cu_3.58(1)Bi_4.42(1)Se_6.84(2)Cl_3.16(2) (δ = 0.58) and Cu_4.52(1)Bi_3.48(1)Se_4.96(2)Br_5.04(2) (δ = 1.52) crystallize isostructural in the orthorhombic space group type Pnnm with a = 1332.3(1)/1340.2(3) pm, b = 1683.7(2)/1717.2(1) pm, and c = 406.2(1)/407.1(2) pm. The new structure type resembles in some aspects the hollandite as well as the pavonite type. A framework of face‐ and edge‐sharing anion polyhedra around Bi³⁺ cations hosts Cu⁺ cations. The characteristic motif is an infinite band of polyhedra that has the width of five polyhedra, with three octahedra being enclosed by capped trigonal prisms. The octahedrally coordinated Bi³⁺ cations are partially substituted by Cu⁺ (in octahedra faces), while Se^2– anions are replaced by X^–. The sulfide iodide Cu_3.33(2)Bi₂S_3.33(2)I_2.67(2) crystallizes in the monoclinic space group C2/m with a = 2803.6(9) pm, b = 409.9(1) pm, c = 1058.0(3) pm, and β = 110.68(2)°. Double strands of face‐sharing [BiS_1/1S_2/2I_4/4] as well as [BiS_3/3I_2/2(S_0.33/I_0.67)_2/2] polyhedra run along [010]. In between them, the Cu⁺ cations are spread over numerous closely spaced sites. They define a ladder‐shaped continuous path for ion conduction along [010].