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Issue 19, 2014
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Structure and thermal expansion of the tungsten bronze Pb2KNb5O15

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The structure and thermal expansion behavior of the tetragonal tungsten bronze oxide Pb2KNb5O15 were investigated by neutron powder diffraction and high-temperature X-ray diffraction. Below the Curie temperature, TC (orthorhombic phase, TC ≈ 460 °C), the cell parameters a and c increase with temperature, while b decreases. The thermal expansion coefficients are αa = 1.29 × 10−5 °C−1, αb = −1.56 × 10−5 °C−1, and αc = 1.62 × 10−5 °C−1. Temperature-dependent second harmonic generation (SHG), dielectric, and polarization–electrical field (PE) hysteresis loop measurements were performed to study the symmetry and electric properties. We show that the distortion and cooperative rotation of NbO6 octahedrons are directly responsible for the negative thermal expansion coefficient along the polar b axis. It is suggested that Pb–O covalency, especially in the large and asymmetric pentagonal prisms, may be related to orthorhombic distortion and abnormal spontaneous polarization along the b axis. This study shows that tungsten bronze families are possible candidates for exploring negative thermal expansion materials.

Graphical abstract: Structure and thermal expansion of the tungsten bronze Pb2KNb5O15

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The article was received on 27 Nov 2013, accepted on 21 Jan 2014 and first published on 23 Jan 2014

Article type: Paper
DOI: 10.1039/C3DT53340A
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Dalton Trans., 2014,43, 7037-7043

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    Structure and thermal expansion of the tungsten bronze Pb2KNb5O15

    K. Lin, H. Wu, F. Wang, Y. Rong, J. Chen, J. Deng, R. Yu, L. Fang, Q. Huang and X. Xing, Dalton Trans., 2014, 43, 7037
    DOI: 10.1039/C3DT53340A

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