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.

Synthesis and structural studies of cation-substituted Aurivillius phases ASrBi2Nb2TiO12

“…Recently, Sivakumar and Gopalakrishnan [9] have shown it is possible to form Aurivillius-type oxides from layered Ruddlesden-Popper or Dion-Jacobson type oxides by metathesis reactions with PbBiO 2 Cl. The same group also recently reported that reaction of n ¼ 2 Aurivillius oxide SrBi 2 Nb 2 O 9 with the perovskite NaTaO 3 yielded the n ¼ 3 oxide SrNaBi 2 Nb 2 TaO 12 under mild conditions [10]. These studies demonstrate that it is possible to build-up complex inorganic structures from simpler building blocks, in a manner analogous to that routinely used in molecular systems.…”

“…Mandal et al [10] recently postulated that the incorporation of cations, such as Sr, that lack a s 2 lone pair electron into the perovskite slabs may force the structure to remain centrosymmetric. The demonstration here that the oxides ASrBi 2 Nb 2 TiO 12 where the perovskite-type A site contains appreciable amounts of alkaline earth cations and have structures that can be refined in the non-centrosymmetric space group B2cb demonstrates this postulate to be incorrect.…”

Structural changes in the homologous series of the Aurivillius phases Bi+1Fe−3Ti3O3+3

“…The B(2) sites (terminal octahedra) are preferentially occupied by Nb (Nb/Ta: 74/26) and the B(1) sites (central octahedra) by Ta (Nb/Ta: 52/48). According to[14], a reference to which is made in[13], a similar distribution of Nb and Ti cations over the sites is observed for the three-layer Aurivillius phases of the formula Bi 2 Sr 2 Nb 2 TiO 12 . The neutron Rietveld refinement for the threelayer Aurivillius phases Bi1.8 Sr 2.2 Nb 2.2 Ti 0.8 O 12 , has determined a slight preference of Nb for the B(2) sites (Nb/Ti: 78/22) in comparison with the inner B(1) site (Nb/Ti: 64/36)…”

“…The distribution of octahedral cations over the nonequivalent sites in the perovskite-like block for the three-layer Aurivillius phases Bi 2 SrNaNb 2 TaO 12 and Bi 2 Sr 2 Nb 2.5 Fe 0.5 O 12 is investigated in [13]. The occupation of sites was determined by the Rietveld refinement of the powder X-ray diffraction data.…”

“…It was demonstrated that despite the chemical similarity of Nb and Ta, their distribution [15]. According to [13], Fe cannot be found at the B(2) site (Nb/Fe: 100/0) in the Aurivillius phases of the formula Bi 2 Sr 2 Nb 2.5 Fe 0.5 O 12 , since Fe occupies the B(1) site together with Nb (Nb/Fe: 50/50).…”