Ordered Structure and Thermal Expansion in Tungsten Bronze Pb2K0.5Li0.5Nb5O15

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• 作者：Kun Lin ; Yangchun Rong ; Hui Wu ; Qingzhen Huang ; Li You ; Yang Ren ; Longlong Fan ; Jun Chen ; Xianran Xing
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：September 2, 2014
• 年：2014
• 卷：53
• 期：17
• 页码：9174-9180
• 全文大小：541K
• ISSN：1520-510X

文摘

The crystal structure and thermal expansion behaviors of a new tetragonal tungsten bronze (TTB) ferroelectric, Pb₂K_0.5Li_0.5Nb₅O₁₅, were systematically investigated by selected-area electron diffraction (SAED), neutron powder diffraction, synchrotron X-ray diffraction (XRD), and high-temperature XRD. SAED and Rietveld refinement reveal that Pb₂K_0.5Li_0.5Nb₅O₁₅ displays a commensurate superstructure of simple orthorhombic TTB structure at room temperature. The structure can be described with space group Bb2₁m. The transition to a paraelectric phase (P4/mbm) occurs at 500 掳C. Compared with Pb₂KNb₅O₁₅ (PKN), the substitution of 0.5K⁺ with small 0.5Li⁺ into PKN causes the tilting of NbO₆ octahedra away from the c axis with 螖胃 鈮?10掳 and raises the Curie temperature by 40 掳C, and the negative thermal expansion coefficient along the polar b axis increases more than 50% in the temperature range 25鈥?00 掳C. We present that, by introduction of Li⁺, the enhanced spontaneous polarization is responsible for the enhanced negative thermal expansion along the b axis, which may be caused by more Pb²⁺ in the pentagonal caves.