The new compound NaCu 4 Se 4 forms by the reaction of CuO and Cu in a molten sodium polyselenide flux, with the existence of CuO being unexpectedly critical to its synthesis. It adopts a layered hexagonal structure (space group P6 3 /mmc with cell parameters a = 3.9931(6) Å and c = 25.167(5) Å), consisting of infinite two-dimensional [Cu 4 Se 4 ] - slabs separated by Na + cations. X-ray photoelectron spectroscopy suggests that NaCu 4 Se 4 is mixed-valent with the formula (Na + )(Cu + ) 4 (Se 2- )(Se - )(Se 2 ) 2- . NaCu 4 Se 4 is a p-type metal with a carrier density of â10 21 cm -3 and a high hole mobility of â808 cm 2 V -1 s -1 at 2 K based on electronic transport measurements. First-principles calculations suggest the density of states around the Fermi level are composed of Cu-d and Se-p orbitals. At 2 K, a very large transverse magnetoresistance of â1400% was observed, with a nonsaturating, linear dependence on field up to 9 T. Our results indicate that the use of metal oxide chemical precursors can open reaction paths to new low-dimensional compounds.
ASJC Scopus subject areas
- Colloid and Surface Chemistry