Cation disorder and structural studies on Bi4a?’e?‘￥Nde?‘￥Ti3O12 (0.0 a‰¤ e?‘￥ a‰¤ 2.0)

摘要

Here we report the results of combined powder X-ray and neutron diffraction studies of Bi4a?’e?‘￥Nde?‘￥Ti3O12 (0.0 a‰¤ e?‘￥ a‰¤ 2.0) compositions. The parent Bi4Ti3O12 has an orthorhombic lattice (space group: B2cb) with unit cell parameters e?‘? = 5.4432(5) ?…, e?‘? = 5.4099(5) ?… and e?‘? = 32.821(2) ?…, and e?‘‰ = 966.5(1) ?…3. This orthorhombic lattice is retained in all the studied compositions. The unit cell parameters gradually decrease with Nd 3+ ion concentration with a discontinuity at e?‘￥ = 0.75. Orthorhombicity of the lattice decreases with increase in Nd3+ content in the lattice. The orthorhombic unit cell parameters for a representative Bi2Nd2Ti3O12 composition are: e?‘? = 5.3834(9), e?‘? = 5.3846(9) and e?‘? = 32.784(1) ?…. The observed orthorhombic distortion at e?‘￥ = 2.0 is very small and thus the crystal structure apparently has a pseudo-tetragonal lattice. In addition, Nd3+ preferentially substitutes in the perovskite slab of the Aurivillius structure. The fraction of Nd3+ in the fluorite slab increases with increase in Nd3+ contents.