Jaime Llanos

ELECTRON TRANSFER AND ELECTRONIC STRUCTURE OF KCUFES2

Abstract The electron transfer that occurs in the insertion of potassium in CuFeS 2 has been analyzed by two different techniques. The binding energies of the core electrons of CuFeS 2 , KCuFeS 2 and K x CuFeS 2 ( x ≈ 0) has been studied by XPS experiments, while the band structure of these phases has been investigated by tight-binding EH calculations. Both experimental and numerical results strongly support the belief that the insertion reaction induces a redox process in the starting CuFeS 2 , by which the Fe 3+ ions are reduced to Fe 2+ . Upon removal of the potassium ions, the Fe 2+ ions are oxidized to Fe 3+ . Copper atoms do not participate in the redox reaction.

Synthesis and crystal structure of layered chalcogenides [KCuFeS2 and KCuFeSe2]

Abstract The new layer chalcogenides KCuFeS 2 and KCuFeSe 2 have been prepared from the copper iron chalcogenide and potassium carbonate. Both phases crystallize with tetragonal symmetry, in the space group I4/mmm (Nr 139) with a = 383.7 (1) pm, c = 1338.4 (4) pm and a = 397.9 (2) pm, c = 1378.7 (54) pm respectively in the ThCr 2 Si 2 -type structure. The chalcogen atoms form bidimensional layers of edge sharing pyramids. Copper and iron are statistically distributed in tetrahedral sites. The potassium ions are placed in cubic sites between the layers.

Synthesis, physical and optical properties, and electronic structure of the rare-earth oxysulfides Ln2O2S (Ln=Sm, Eu)

The compounds Ln{sub 2}O{sub 2}S (Ln=Sm, Eu) were prepared from the respective oxides by partial sulfurization under flowing CS{sub 2}/Ar/O{sub 2} atmosphere. The main feature of the structure is the packing of S{sup 2-} and O{sup 2-} anions with Ln{sup 3+} located in the center of a capped octahedron. Electrical conductivity measurements on pressed pellets showed that both phases are highly resistive with conductivities lower than 10{sup -8} S cm{sup -1} at room temperature. The optical bandgaps were assessed at 4.2 and 4.4 eV for Sm{sub 2}O{sub 2}S and Eu{sub 2}O{sub 2}S, respectively. Electronic structure calculations were performed by means of extended Hueckel tight-binding method. The insulating properties are in good agreement with the results predicted by theoretical calculations.

Synthesis and structural characterization of two intercalated lithium and sodium copper iron selenides: LiCuFeSe2 and NaCuFeSe2

Abstract The not new phases LiCuFeSe2 and NaCuFeSe2 were prepared from the corresponding carbonates and CuFeSe2. They crystallize as the isostructural sulphide phases LiCuFeS2 and NaCuFeS2 in the trigonal space group P 3 m1 (No. 164) in a layered Li2FeS2 structure type. The Se atoms form an h.c.p. array, the copper and iron atoms are statistically distributed in the tetrahedral sites whereas the alkali metals are placed in the octahedral sites in the van der Waals gap.

Electron transfer in the insertion of alkali metals in chalcopyrite

Abstract The insertion of alkali metals in chalcopyrite has been investigated by X-ray photoelectron spectroscopy and band structure calculations of the extended Huckel type. The results show that the alkali metal insertion (removal) reaction, which corresponds to the discharge (charge) process of the electrochemical system Li Li 1+ CuFeS 2 , is related to an electron transfer involving mainly the Fe ions. The experimental and theoretical data indicate that the Cu atoms do not participate in the redox reaction.

A NEW STRUCTURAL MODIFICATION OF STANNITE

This work was supported by FONDECYT contract 1960372 and the Programa de Intercambio Cientifico CONICYT (Chile) and CSIC (Spain), grant 96022.

Polyoxyethylene intercalation in lamellar copper iron sulfide

Abstract The insertion of polyethyleneoxide in a lamellar copper iron sulfide of formula CuFeS 2 by an exchange reaction of potassium from KCuFeS 2 with an aqueous solution of the polymer was performed. The characterization of the new compound by X-ray diffraction and IR absorption spectroscopy shows that the layer structure of the precursor has been retained and that the polymer adopts a zigzag configuration between the layers.

Structure refinement of samarium monothio oxide

This work was supported by FONDECYT contracts 1960372 and 1990364 and the Programa de Intercambio Cientifico CONICYT (Chile) and CSIC (Spain), grant 96022.

Structure refinement of monoclinic V3S4

Abstract The structure of monoclinic V 3 S 4 was refined using single crystal X-ray data. This modification crystallizes isostructural with Cr 3 S 4 , space group C 2/ m with a = 1263.8(2) pm, b = 329.4(1) pm, c = 587.8(1) pm and β = 115.68(1)°. The sulfur-metal distances are quite similar to those reported for the hexagonal modification of V 3 S 4 . Nevertheless, the monoclinic modification leaves smaller empty channels than those observed in the hexagonal modification.

Ordering of transition metal atoms in MCuFeS2 (M = Li, Na): electronic structure and Monte Carlo simulations

Abstract Previous X-ray investigations have shown the absence of long-range order in the distribution of transition metal atoms on the tetrahedral sites of the layered MCuFeS 2 (M = Li, Na) compounds. We have analyzed the band structure of these crystals for several distributions of Cu and Fe atoms by an extended Huckel Hamiltonian. The electronic structure study supports that Fe-Fe interactions are energetically more favorable than Cu-Fe contacts. Effective potential parameters for the interaction between transition metal atoms were derived from the calculated electronic energies. This potential model was used to investigate the equilibrium (Cu, Fe) distribution as a function of the temperature by Monte Carlo simulations. At the synthesis temperature of NaCuFeS 2 ( T f = 1070 K), the (Cu, Fe) distribution does not display long-range order, a fact that agrees with X-ray diffraction studies, but is characterized by short-range order favoring the formation of chains and clusters of Fe atoms.