Novel synthesis methods have been investigated for the preparation of Bi4Ti3O12 ferroelectric Aurivillius-type powders, namely, the wet no-coprecipitated chemistry using a n-butylamine aqueous solution and two mechanochemical activation techniques (vibrating and planetarium mills). For the sake of comparison, Bi4Ti3O12 powders were also produced by the traditional ceramic route. The syntheses of the crystalline phases were obtained by annealing of the precursors at different temperatures and times. Both the precursors and the thermally treated products were characterized by means of X-ray powder diffraction, thermal analysis, and scanning electron microscopy. The Aurivillius phase was found to appear at 600 °C for vibrating and 500 °C for planetarium-milled precursors. These temperatures are 250−350 °C lower than those reported for the traditional ceramic route (850 °C). Moreover, the stabilization at room temperature of a new fluorite Bi−Ti−O structure was obtained by use of the planetarium milling precursor. The microstructure of the powder investigated by SEM was correlated with the XRD results. In particular, monolithic Bi4Ti3O12 grains of a few microns in size were achieved by means of the wet chemistry method.

By x-ray powder diffraction and the Rietveld refinement method, the atomic positions in CuInSe2 were determined for compositions close to stoichiometry. The Se position, x(Se), was found to be correlated to the Cu content. According to a model proposed by Jaffe and Zunger [Phys. Rev. B 29, 1882 (1984)], changes in x(Se) induce a variation in the optical band gap, Eg. This could explain the spread in energy gap, Eg, found by many authors for this compound. The increase in the lattice parameter, a, correlated with the difference between the energy dispersive analysis of x rays and x-ray diffraction determined Cu contents, suggests the presence of a fraction of Cu atoms as interstitials.

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