The role of Tb-doping on the structural and functional properties of Bi+(4-x)Tb_xTi_3O_(12) ferroelectric phases with the Aurivillius type structure

摘要

Synthesis, crystal structure, dielectric, and magnetic properties of the Aurivillius phase Bi_(4-x_Tb_xTi_3-O_(12) (x = 0.0, 0.4, 0.6, 0.8) are reported. The samples were synthesized using standard solid state reaction technique. The thermal stability of the obtained solid solutions was investigated. For x ≤ 0.8, the samples crystallized in an orthorhombic symmetry. All the samples showed finite second harmonic generation response indicating a non-centrosymmetric structure. The structural data could be refined using the polar orthorhombic space group B2cb. The orthorhombicity decreases with an increase in the Tb~(3+) concentration. The orthorhombic distortions in these compositions are related to the Bi~(3+)-based perovskite sublattice. Our results indicate that the non-lone pair Tb~(3+) cations preferentially occupy the perovskite sublattice initially, but with an increase in the doping concentration they can partially substitute the Bi~(3+) ions in the fluorite block. Temperature dependent dielectric measurements revealed a decrease in the ferroelectric Curie temperature T_C with an increase in x from T_C = 904 K (for x = 0) to 877 K (for x = 0.4). Further increase in x led to a cross-over to a relaxor-type behavior. Magnetic measurements showed that the samples are paramagnetic down to 5 K.