An Original Polymorph Sequence in the High-Temperature Evolution of the Perovskite Pb2TmSbO6

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• 作者：Sebastin A. Larrgola ; Jos A. Alonso ; Denis Sheptyakov ; Miguel Alguer ; Angel Muoz ; Vladimir Pomjakushin ; Jos C. Pedregosa
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：October 20, 2010
• 年：2010
• 卷：132
• 期：41
• 页码：14470-14480
• 全文大小：458K
• 年卷期：v.132,no.41(October 20, 2010)
• ISSN：1520-5126

文摘

The synthesis, crystal structure, and dielectric properties of the novel double perovskite Pb₂TmSbO₆ are described. The room-temperature crystal structure was determined by ab initio procedures from neutron powder diffraction (NPD) and synchrotron X-ray powder diffraction (SXRPD) data in the monoclinic C2/c (No. 15) space group. This double perovskite contains a completely ordered array of alternating TmO₆ and SbO₆ octahedra sharing corners, tilted in antiphase along the three pseudocubic axes, with an a⁻b⁻b⁻ tilting scheme, which is very unusual in the crystallochemistry of perovskites. The lead atoms occupy a highly asymmetric void with 8-fold coordination due to the stereoactivity of the Pb²⁺ lone electron pair. This compound presents three successive phase transitions in a narrow temperature range (at T1 = 385 K, T2 = 444 K, and T3 = 460 K in the heating run) as shown by differential scanning calorimetry (DSC) data. The crystal structure and temperature-dependent NPD follow the space-group sequence C2/c → P2₁/n → R → Fmm. This is a novel polymorph succession in the high-temperature evolution of perovskite-type oxides. The Tm/Sb long-range ordering is preserved across the consecutive phase transitions. Dielectric permittivity measurements indicate the presence of a paraelectric/antiferroelectric transition (associated with the last structural transition), as suggested by the negative Curie temperature obtained from the Curie−Weiss fit of the reciprocal permittivity.