New insights into BaTi1-xSnxO3 (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

Abstract

Neutron powder diffraction (NPD) was employed to further investigate the BaTi1-xSnxO3 (BTS) system previously studied by X-ray diffraction. The room-temperature phase compositions and crystal structures of BTS samples with x = 0, 0.025, 0.05, 0.07, 0.10, 0.12, 0.15 and 0.20 were refined by the Rietveld method using NPD data. It is well known that barium titanate powder (x = 0) crystallizes in the tetragonal P4mm space group. The crystal structures of the samples with 0.025 ≤ x ≤ 0.07 were refined as mixtures of P4mm and Amm2 phases; those with x = 0.1 and 0.12 show the coexistence of rhombohedral R3m and cubic phases, while the samples with x = 0.15 and 0.20 crystallize in a single cubic phase. Temperature-dependent NPD was used to characterize the BaTi0.95Sn0.05O3 sample at 273, 333 and 373K, and it was found to form single-phase Amm2, P4mm and structures at these respective temperatures. The NPD results are in agreement with data obtained by differential scanning calorimetry and dielectric permittivity measurements, which show a paraelectric-ferroelectric transition (associated with structural transition) from to P4mm at about 353K followed by a P4mm to Amm2 phase transition at about 303K.Neutron powder diffraction (NPD) data were used to study the evolution of the crystal structure of BaTi1-xSnxO3 (BTS) induced by variations in the Ti/Sn ratio and temperature. The results obtained from NPD data are somewhat different from those previously determined from X-ray diffraction data, because NPD allows for a more precise determination of the Ba - O bond distances, fractional atomic coordinates and displacement parameters.