From the reaction of the metallic elements in molten alkali metal/polychalcogenide fluxes, we have synthesized KCuCe2S6 (I) and K2Cu2CeS4 (II). Isolated from a 2/0.5/1/8 mixture of K2S/Cu/Ce/S heated at 270 °C for 6 d, I crystallizes in the space group C2/c (no. 15) with a = 6.859(2) Å, b = 21.154(2) Å, c = 6.8599(8) Å, 0 = 105.41(2)°, and Z = 4. The structure of I features (CuCe2S6)nn- anionic layers composed of [CeS8] bicapped trigonal prisms connected in the ZrSe3 fashion with Cu+ residing in tetrahedral sites within the layers and K+ cations in the interlayer gallery. Diffuse reflectance measurements have shown an approximated band gap of 1.8 eV for I, and magnetic studies exhibit Curie-Weiss paramagnetic behavior at temperatures above 160 K with μeff = 3.08 μB/formula. Isolated from a 4.2/0.5/0.25/8 mixture of the above reagents heated at 260 °C for 5d, II crystallizes in the C2/m space group (no. 12) with a = 14.320(3) Å, b = 3.961(1) Å, c = 7.496(2) Å, β = 109.77(2)°, and Z = 2. Compound II is also a layered structure in which Ce atoms, octahedrally coordinated by S, and Cu, tetrahedrally coordinated by S, form anionic layers related to Mg2SiO4 (olivine) with K+ in the interlayer gallery. From magnetic susceptibility studies, a μeff of 2.38 μb was estimated above 150 K corresponding to the value for a lone Ce3+. The compound's oxidation states are formalized as K2(Cu1+)2(Ce3+)(S2-)3(S1-). Below 150 K, the material shows non-Curie-Weiss behavior, exhibiting a decreasing μeff. Thermopower studies on II show p-type carriers; however, the conductivity is low and increases with increasing temperature, suggesting a low carrier mobility possibly arising from small polaron formation.
ASJC Scopus subject areas
- Colloid and Surface Chemistry