Physical properties of new, lead free (Na0.5Bi0.5)(1−x)BaxTi(1−x)(Fe0.5Nb0.5)xO3 ceramics
Résumé
This study reports on the synthesis of polycrystalline samples of (Na0.5Bi0.5)((1-x))BaxTi(1-x)(Fe0.5Nb0.5)(x)O-3 with x=0, 0.025, 0.05, 0.075, and 0.1, using the solid-state reaction technique. It investigates the effects of the substitution of sodium and bismuth by barium in the A site and of titanium by iron and niobium in the B site with regard to the free NBT symmetry and dielectric properties were investigated. The crystallographic and dielectric properties were also investigated. The diffractograms showed that all the samples had a single phase character. The increase of ceramic lattice parameters induced an increase in the size of the perovskite lattice. This increase was caused by the increase of the radii of the A and B sites. Room temperature X-ray data revealed that the ceramic structures underwent a gradual distortion with the increase in the composition fraction. Dielectric permittivity was measured in the temperature range of 120-780 K with frequencies ranging from 1 to 10(3) KHz. Three anomalies, namely T-d, T-1 and T-m, were detected and noted to coexist at lower T-d and T-m as the rate of substitutions increased. All the samples exhibited a diffuse phase transition and implied better dielectric permittivity maxima values at temperatures approaching room temperature, since the substitution rate values increased more than that of pure NBT. A relaxor behavior with Delta T-m= 14K and epsilon'(rmax) =3876 at 1 kHz was observed for (Na0.5Bi0.5)(0.9)Ba0.1Ti0.9(Fe0.5Nb0.5)(0.1)O-3 ceramic.