Cobalt aluminate CoAl 2 O 4 powder, constituted of nano-sized crystallites, is prepared, involving the reactivity of AlCl 3 and CoCl 2 with molten alkali-metal nitrates. The reaction at 450 °C for 2 h leads to a mixture of spinel oxide Co 3 O 4 and amorphous γ-Al 2 O 3 . It is transformed into the spinel oxide CoAl 2 O 4 by heating at 1000 °C. The powders are mainly characterized by XRD, FTIR, ICP, electron microscopy and diffraction, X-EDS and diffuse reflection. Their properties are compared to those of powders obtained by solid state reactions of a mechanical mixture of chlorides or oxides submitted to the same thermal treatment.

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Fe-Cr/Al2O3 metal-ceramic composites prepared by hydrogen reduction at different temperatures and for different periods have been investigated by a combined use of Mossbauer spectroscopy, x-ray diffraction, transmission electron microscopy, and energy-dispersive x-ray spectroscopy in order to obtain information on the nature of the metallic species formed. Total reduction of Fe3+ does not occur by increasing the reduction time at 1320 K from 1 to 30 h, and the amount of superparamagnetic metallic species is essentially constant (about 10%). Temperatures higher than 1470 K are needed to achieve nearly total reduction of substitutional Fe3+. Interestingly, iron favors the reduction of chromium. The composition of the Fe-Cr particles is strongly dependent on their size, the Cr content being higher in particles smaller than 10 nm.

a b s t r a c tCuInS 2 was synthesized, with a yield of 70% by reaction in molten KSCN at 400 1C of CuCl 2 and InCl 3 with a ratio KSCN/Cu ¼ 15. The homogeneous powder obtained is constituted of nano-sized grains (70-100 nm), with a specific surface area of 6 m 2 /g and a band gap Eg of 1.5 eV.

Cuprous oxide and zinc oxide nanoparticles were prepared at room temperature by inorganic polycondensation. X-ray diffraction (XRD) analyses show that the oxide phases formed are pure and well crystallized. The spark plasma sintering (SPS) technique was successfully used to prepare dense nanoceramics with superimposed layers of Cu 2 O and ZnO nanopowders. Sintering conditions were optimized to densify the ceramics without phase transformation or diffusion. These ceramics were also characterized by XRD and scanning electron microscopy (SEM), as well as X-ray computed tomography (XCT). SEM and XCT showed that nanograins are preserved after SPS throughout both oxide materials, while a smaller layer (*20 lm) of pure oxide phase with larger grains is formed in between Cu 2 O and ZnO during the sintering process. The SPS technique results in high material density, with the absence of porosity and cracks, homogenous distribution, and a good phase separation. This is the first time that such as-prepared dense oxide-based heterojunction exhibits a photovoltaic effect under illumination opening a new route for preparing solar cells.

Nano-crystalline particles of Cu2ZnSnS 4 have been successfully synthesized by a relatively low-temperature molten sait technique. The reaction of metal chlorides with KSCN at 400°C for 24 h led to the Cu2ZnSnS4 phase. The phase purity of Cu2ZnSnS4 nanocrystals has been confirmed by X-ray diffraction and Raman spectroscopy. The morphology and the crystallite size were evaluated by scanning and transmission electron microscopies. The Cu2ZnSnS 4 nanocrystals possess an optic.al band gap of 1.5 eV, very close to the theoretical optimum for solar energy conversion.