Heterovalent cation-substituted Aurivillius phases, $Bi_{2}SrNaNb_{2}TaO_{12}$ and $Bi_{2}Sr_{2}Nb_{3-x}M_{x}O_{12}$ (M = Zr, Hf, Fe, Zn)

Mandal, TK and Sivakumar, T and Augustine, S and Gopalakrishnan, J (2005) Heterovalent cation-substituted Aurivillius phases, $Bi_{2}SrNaNb_{2}TaO_{12}$ and $Bi_{2}Sr_{2}Nb_{3-x}M_{x}O_{12}$ (M = Zr, Hf, Fe, Zn). In: Materials Science And Engineering B-Solid State Materials For Advanced, 121 (1-2). pp. 112-119.

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Abstract

We describe the synthesis and structural characterization of newaliovalent 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 11, 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-Tellereffect associated with $d^0$ cations.

Item Type:	Journal Article
Publication:	Materials Science And Engineering B-Solid State Materials For Advanced
Publisher:	Elsevier Science SA
Additional Information:	Copyright for this article belongs to Elsevier.
Keywords:	Ceramics;Oxides;Layer structures;X-ray diffraction
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	04 Aug 2005
Last Modified:	19 Sep 2010 04:19
URI:	http://eprints.iisc.ac.in/id/eprint/3479

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