Crystallographic structure and electron density of Ba_1-x Pb_xTiO₃ ceramic

The effect of Pb on crystallographic structure and electron density of Ba_1-xPb_xTiO₃ ceramic, where x (nominal) = 0.5, has been investigated by XRD Phillips 1877. The samples were synthesized using powder metallurgy method from BaCO₃, PbCO₃ and TiO₂, with purity better than 99%, available commercially from E-Merck. The x-ray diffraction data obtained at room temperature were refined using the crystallographic software package GSAS. The structural analysis shows that the crystal is Ba_0.7Pb_0.3TiO₃ with the perovskite-type BaTiO₃ structure, the space group is tetragonal P4mm with a = 3.943(1) Å, c = 4.055 Å and V = 63.035 ų. These results imply that Pb has no effect on the non-centrosymmetric structural change of barium titanate, except to slightly contract a and b parameters and to extend c parameter, the c/a ratio becomes 1.03. The studies on electron density show that the electron density measurements are consistent with the calculated structural parameters, it has maximum Δρ = 7.965 eÅ ^-3 and minimum_Δρ = -2.555 eÅ^-3. The final results show that there is an increasing of electron density at the substitute ion positions with maximum ρ = 180.069 eÅ ^-3 and 172,105 eÅ^-3 for the observed and the calculated values, respectively. These values are greater than the one from barium titanate. Approximately, the observed (calculated) maximum electron density increases by 56% (53%) as 33% Pb substitutes Ba.