ic501189n_si_002.cif (21.4 kB)
Ordered Structure and Thermal Expansion in Tungsten Bronze Pb2K0.5Li0.5Nb5O15
datasetposted on 2014-09-02, 00:00 authored by Kun Lin, Yangchun Rong, Hui Wu, Qingzhen Huang, Li You, Yang Ren, Longlong Fan, Jun Chen, Xianran Xing
The crystal structure and thermal expansion behaviors of a new tetragonal tungsten bronze (TTB) ferroelectric, Pb2K0.5Li0.5Nb5O15, 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 Pb2K0.5Li0.5Nb5O15 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 °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 Δθ ≈ 10° and raises the Curie temperature by 40 °C, and the negative thermal expansion coefficient along the polar b axis increases more than 50% in the temperature range 25–500 °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.
expansion behaviors0.5 Li0.5 Kspace group Bb 21mThermal Expansionexpansion coefficientXRDCurie temperaturePb 2K displaystungsten bronzepentagonal cavesTungsten Bronze Pb 2K crystal structurec axisRietveld refinementPb 2KNbPKN causesb axis increasesb axisSAEDparaelectric phasePb 2KNbO 6 octahedraTTB structurediffractionroom temperature