Heterovalent cation-substituted Aurivillius phases, Bi2SrNaNb2TaO12 and Bi2Sr2Nb3−xMxO12 (M = Zr, Hf, Fe, Zn)

Abstract We describe the synthesis and structural characterization of new aliovalent cation-substituted n  = 3 Aurivillius phases of the formulas, Bi 2 SrNaNb 2 TaO 12 ( I ), Bi 2 Sr 2 Nb 2 ZrO 12 ( II ), Bi 2 Sr 2 Nb 2.5 Fe 0.5 O 12 ( III ) and Bi 2 Sr 2 Nb 2.67 Zn 0.33 O 12 ( IV ). Energy dispersive X-ray (EDX) investigation of the chemical compositions showed that while cation-stoichiometric materials are formed for I and II , single-phase materials are obtained only for the compositions given for III and IV suggesting that the compositions tend to be oxygen-stoichiometric. The results show that aliovalent cation-substituted n  = 3 Aurivillius phases similar to Bi 2 Sr 2 Nb 2 M IV O 12 (M = Ti, Mn) exist for several metal cations, viz., Ta V , Zr IV , Fe III and Zn II . Refinement of the crystal structures from the powder X-ray diffraction (XRD) data for I and III revealed that bismuth is essentially confined to the Bi 2 O 2 layers and the aliovalent cation shows a preference for the middle perovskite sheet. The present work is significant for two reasons: firstly, the presence of cations such as Sr 2+ , Na + (that do not contain lone pair s 2 electrons) in the perovskite slabs seems to render the structure centrosymmetric; secondly, a preferential/partial ordering of octahedral site cations in the perovskite slabs obtains in these materials, that seems to be dictated by a second order Jahn–Teller effect associated with d 0 cations.