Conversion of an Aurivillius Phase Bi 2 SrNaNb 3 O 12 into Its Protonated Form via Treatment with Various Mineral Acids
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Conversion of an Aurivillius Phase Bi2SrNaNb3O12 into Its Protonated Form via Treatment with Various Mineral Acids Masashi Shirata, Yu Tsunoda, Wataru Sugimoto,1 and Yoshiyuki Sugahara Department of Applied Chemistry, School of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555 JAPAN 1Department of Fine Materials Engineering, Faculty of Textile Science and Technology, Shinshu University, Ueda, Nagano, 386-8567 JAPAN ABSTRACT A protonated form of a layered perovskite was prepared from an Aurivillius phase Bi2SrNaNb3O12 via acid treatments, and the effect of the type of mineral acids was investigated. The treatment with HX (X = Cl, Br, I) resulted in the formation of a protonated form H1.8[Sr0.8Bi0.2NaNb3O10], while no reactions were observed for HNO3 and H2SO4 under the present experimental conditions. All the products obtained by HX-treatments exhibited layered structures and the structures of the perovskite-like slabs were preserved.
INTRODUCTION Layered perovskites possess two-dimensional perovskite-like slabs in their structures. Among them, ion-exchangeable layered perovskites consist of perovskite-like slabs ([An-1BnO3n+1]; A = Sr, Ca, etc., B = Ti, Nb, Ta) and monovalent exchangeable interlayer cations (M; M = Na, K, Rb, etc.) [1]. There have been two homologous series reported, that are called Dion-Jacobson phases (M[An-1BnO3n+1]) [2,3] and Ruddlesden-Popper phases (M2[An-1BnO3n+1]) [4-6]. When these layered perovskites were treated with mineral acids, they were converted into corresponding protonated forms (H[An-1BnO3n+1] and H2[An-1BnO3n+1]) [3,6-8]. These protonated forms exhibit interesting properties including photocatalytic behavior [9], proton conduction [10], and intercalation of organic amines [11]. These protonated forms can also be utilized as precursors for oxide syntheses [12]. Aurivillius phases (Bi2An-1BnO3n+3 or alternately expressed as Bi2O2[An-1BnO3n+1]) are known to exhibit excellent dielectric properties. In terms of structures, they consist of perovskite-like slabs ([An-1BnO3n+1]) and Bi2O2 layers, and it should be noted that the structures of perovskite-like slabs in the Aurivillius phases are identical with those in the aforementioned ion-exchangeable layered perovskites [13]. Suzuki et al. [14] reported the acid treatment of a Bi2SrTa2O9 single crystal, and observed drastic variation in X-ray diffraction patterns; they ascribed this observation to the structural change in the perovskite-like slabs. We have recently reported that HCl-treatment of another Aurivillius phase, Bi2SrNaNb3O12, led to the selective leaching of the Bi2O2 layers and the introduction of protons for charge compensation to form a corresponding protonated form [15]. Since no structural change in the perovskite-like slabs occurred, this reaction is considered to be the conversion of the Aurivillius phase into a protonated form of a Ruddlesden-Popper phase (though the layer charge is slightly reduced from 2- per [An-1BnO3n+1], the general value for the Ruddlesden-Popper phases, to ~1.8- per [An-1
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