The effect of Ag addition on the optical properties of Se90Te10 films

Se₉₀Te_10−xAg_x (0 ≤ x ≤ 6) compositions were prepared by quenching technique. Thin films with different thicknesses of the obtained compositions were deposited on dry clean glass substrates by thermal evaporation technique. Energy dispersive X-ray spectroscopy (EDX) indicates that samples are nearly stoichiometric. X-ray diffraction patterns indicate that they are in the amorphous state. The optical constants, the refractive index n and the absorption index k, have been calculated from transmittance T and reflectance R through the spectral range of 400-2500 nm for the studied films with different thicknesses (165-711 nm). From the analysis of refractive index n data, high frequency dielectric constant ?_∞ was determined. Both ?_∞ and n are found to decrease with the increase of Ag content. The optical band gap is calculated for all compositions from the absorption coefficient analysis. The effect of the Ag addition on the obtained optical parameters has been discussed. The analysis of absorption index k data, revealed the existence of allowed indirect transitions for all compositions. It is indicated also that increase with increasing Ag content.     

Relaxor behavior of K0.5La0.5Bi2Ta2O9 ceramics

Potassium lanthanum bismuth tantalate (K_0.5La_0.5Bi₂Ta₂O₉), a new relaxor ferroelectric was synthesized via the solid-state reaction route. X-ray structural studies along with Rietveld refinement confirmed it to be an n=2 member of the Aurivillius family of oxides and the refined lattice parameters are , and . The appearance of 1/2{h00} and 1/2{hk0} type superlattice reflections in the electron diffraction patterns reflected the presence of ordered polar regions. A broad dielectric peak associated with frequency dependent dielectric maximum temperature was observed. The value of the diffuseness parameter γ=1.93, obtained from the fit of a modified Curie-Weiss law established the relaxor nature of the title compound. The dielectric relaxation obeyed the Vogel-Fulcher relation wherein and . The relaxor behavior was attributed to the local polar ordering on A-sites.