title: NaBa2Cu3S5: a doped p-type degenerate semiconductor.
abstract: Mixed S(2-/)S(1-) 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(+)3S3](3-)S2(2-) crystal structure contains layers of edge sharing CuS4 tetrahedra and sheets of S2(2-) dimers. These layers are separated by mixed Ba/Na cation layers. The conductivity of the single crystals of NaBa2Cu3S5 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 × 10(21) cm(-3) and a hole mobility of ∼2 cm(2) V(-1) s(-1). NaBa2Cu3S5 exhibits temperature-independent Pauli paramagnetism.
authors.affiliation: Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States.
authors.forename: Mihai
authors.initials: M
authors.lastname: Sturza
authors.forename: Fei
authors.initials: F
authors.lastname: Han
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Shoemaker
authors.forename: Christos D
authors.initials: CD
authors.lastname: Malliakas
authors.forename: Duck Young
authors.initials: DY
authors.lastname: Chung
authors.forename: Hosub
authors.initials: H
authors.lastname: Jin
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Freeman
authors.forename: Mercouri G
authors.initials: MG
authors.lastname: Kanatzidis