Non-stoichiometry and electrochemical properties of lithiated iron hydroxysulfides.

LiFeOHS is a material with Li2(OH)2 layers intercalated between Fe2S2 planes. Its hydrothermal synthesis in various concentrations of LiOH yields materials with a high non-stoichiometry of the Li/Fe ratio which can be explained by partial substitution of Li+ for Fe2+ in the Li2(OH)2 layers. Thermogravimetry, X-ray diffraction and Mössbauer studies indicate that the charge balance is obtained by substitution of hydroxyl ions OH- by oxide ions O2-. This material has been tested as an electrode for lithium-ion batteries against lithium metal. Specific capacities above 200 mA h g-1 at C/10 are achieved, involving 1 lithium per chemical formula when cycled between 1 V and 3 V vs. lithium. The first irreversible discharge leads to the insertion of one lithium atom and the evolution of hydrogen gas while iron remains in its +2-oxidation state. An original Li2OFeS oxysulfide is formed. The following reversible oxidation/reduction cycles involve the Fe3+/Fe2+ redox couple between the two limiting compositions: Li2OFeIIS and LiOFeIIIS.

Aqueous-Based Low-Temperature Synthesis and Thin-Film Properties of Oxysulfide BiCuOS Nanoparticles.

BiCuOS is a nontoxic p-type semiconductor that is a promising candidate for photoelectric applications. The formation of thin films with a good electronic transport at the grain boundaries, while avoiding thermal treatment detrimental to its chemical stability is a challenge. We have developed a chemical method for the direct synthesis of stable colloidal suspensions of BiCuOS nanoparticles from soluble precursors. These colloidal solutions were stabilized with a catechol functionalized poly-3-hexylthiophene that allows easy spin-coating deposition and favors electronic transport along the grain boundaries. Stacking of ZnO-BiCuOS layers were achieved, allowing preparation of n-p junctions. These act as rectifying diodes and are strongly photosensitive, with Iph /Idark =85 corresponding to an enhancement of the photocurrent of more than two orders of magnitude compared to that of BiCuOS alone. This energy-efficient and low-cost method is a further step in the development of new sulfide semiconductor devices.

Narrow optical homogeneous linewidths in rare earth doped nanocrystals.

A homogeneous linewidth of 85.6±4.4 kHz is reported in 60 nm Eu3+ doped Y2O3 nanocrystals at 1.3 K. This linewidth was measured by two-pulse photon echoes on highly scattering powders using heterodyne detection. Spectral diffusion was also investigated by three-pulse photon echoes and resulted in a limited broadening of the homogenous linewidth of about 250 kHz over 120 µs. Compared to achievable Rabi frequencies, in the range of several MHz, these values show that rare earth doped nanocrystals can be useful for applications in optical quantum information processing.