Mixed S2-/S1- oxidation states have been discovered in the new quaternary compound NaBa2Cu3S5. Synthesized from the reaction of Cu in a molten alkali metal/polysulfide flux, the compound crystallizes in monoclinic space group C2/m with a = 16.5363(7) Å, b = 5.5374(5) Å, c = 10.3717(10) Å, β = 98.535(8). The Na+ Ba2+2 [Cu+3S 3]3-S22- crystal structure contains layers of edge sharing CuS4 tetrahedra and sheets of S 22- dimers. These layers are separated by mixed Ba/Na cation layers. The conductivity of the single crystals of NaBa 2Cu3S5 is ∼450 S cm-1 at room temperature, and increasing conductivity with decreasing temperature is observed, indicating metallic behavior despite the optical band gap of 0.45 eV. A small positive thermopower (45-55 μV K-1 from 300 K to 500 K) and Hall effect measurements also confirm p-type conductivity with carrier concentration at 200 K of ∼1.6 × 1021 cm-3 and a hole mobility of ∼2 cm2 V-1 s-1. NaBa 2Cu3S5 exhibits temperature-independent Pauli paramagnetism.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry