New insights into BaTi1-xSnxO3 (0 LT = x LT = 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 LT = x LT = 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 Pm (3) over barm phase. Temperature-dependent NPD was used to characterize the BaTi0.95Sn0.05O3 sample at 273, 333 and 373 K, and it was found to form single-phase Amm2, P4mm and Pm (3) over barm 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 para-electric-ferroelectric transition (associated with structural transition) from Pm (3) over barm to P4mm at about 353 K followed by a P4mm to Amm2 phase transition at about 303 K.