Synthesis and Characterization of Cu3NbSe4 and KCu2TaSe4

Abstract

Cu3NbSe4 has been synthesized from a stoichiometric reaction of the elements at 950°C. The material, which has the sulvanite (Cu3VS4) structure, crystallizes in space group T1d-P4̄3m of the cubic system with one formula unit in a cell with a = 5.638(1) Å at - 165°C. Cu3NbSe4 has a three-dimensional structure with edge-sharing of CuSe4 and NbSe4 tetrahedra and corner-sharing among CuSe4 tetrahedra extending equally in all directions. KCu2TaSe4 was prepared from a reaction of K2Se5, Cu, Ta, and Se in the ratio 1:4:2:3 at 850°C. KCu2TaSe4 crystallizes in space group C43 -Cc of the monoclinic system with four formula units in a cell of dimensions a = 5.660(1), b = 18.829(4), c = 7.662(2) Å, β = 90.04(3)° at - 165°C. In this structure the Ta and two independent Cu atoms are in tetrahedral sites. The CuSe4 and TaSe4 tetrahedra share edges and corners to make up two-dimensional layers. These layers are separated from one another by K+ ions. KCu2TaSe4 is not isostructural with KCu2NbSe4, although the structures are similar.