Structural Singularities in Ferroelectric Sr2NaNb5O15

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• 作者：E. Garcí ; a-Gonz&aacute ; lez ; A. Torres-Pardo ; R. Jimé ; nez ; J. M. Gonz&aacute ; lez-Calbet
• 刊名：Chemistry of Materials
• 出版年：2007
• 出版时间：July 10, 2007
• 年：2007
• 卷：19
• 期：14
• 页码：3575 - 3580
• 全文大小：618K
• 年卷期：v.19,no.14(July 10, 2007)
• ISSN：1520-5002

文摘

The structural features of the ferroelectric compound Sr₂NaNb₅O₁₅ have been carefully studied. Adetailed investigation has been performed by means of room temperature (RT) and high temperature(HT) powder X-ray diffraction (XRD), selected area electron diffraction (SAED), high resolution electronmicroscopy (HREM), and impedance spectroscopy. Comparison is done with the barium homologuecompound and the two RT ferroelectric phases can be structurally distinguished. The use of electrondiffraction in combination with HREM has revealed the formation of a superlattice structure of tetragonaltungsten bronze (TTB) at RT. While in Ba₂NaNb₅O₁₅ the incommensurate nature of this RT phase seemsto be doubtless, the Sr₂NaNb₅O₁₅ ferroelectric phase displays a commensurate superstructure of the TTBstructure-type. The RT XRD pattern can be indexed in the Im2a space group. The transition to theparaelectric phase occurs at 518 K, and the material can be indexed in the centrosymmetric P4/mbmspace group. From the Rietveld refinement of this HT phase, disordered distribution of Na and Sr in theA positions of the structure seems to occur, as opposite to the barium compound where barium atomsshow clear preference for the largest A2 sites.