RESUMEN
Lead-free ferroelectric ceramics based on the Na(0.5)Bi(0.5)TiO3 system, in solid solution with Pr(3+) and La(3+), are synthesized by the Pechini method at low temperature. The powders calcined at 700 °C are found to be below 200 nm in mean crystal size. The dielectric properties reveal a diffuse phase transition. In Na(0.5)Bi(0.5)TiO3 ceramics the rhombohedral to tetragonal transition temperature (T(R-T)) appears near 190 °C, and the Curie temperature (T(C)) at 280 °C. These transitions are shifted when Pr(3+) and La(3+) cations are introduced into the lattice. The ferroelectric properties are also affected, causing the remnant polarization and coercive field to diminish with the increase in La(3+) content. In addition, the piezoelectric properties decrease in the same way with La(3+) concentration. Finally, the red luminescence of Pr(3+) is improved when lanthanum concentration is increased.
RESUMEN
Fullerene C60 films deposited by sublimation were irradiated with Kr-F laser in a wide fluence interval from 15 to 40 mJ/cm2. In situ photoacoustic analysis was applied to study the phase transformation during the irradiation. The results obtained were discussed in conjunction with atomic force microscopy (AFM) and Raman spectroscopy data. It was found that for a irradiation fluence interval from 22 to 30 mJ/cm2, 80% of C60 undergoes photopolymerization (presumably through 2 + 2 cycloaddition). For a laser energy higher than 30 mJ/cm2, a new amorphous carbon phase forms, having a large content of diamond-like, tetra-amorphous carbon (ta-C).