Revisiting the Crystal Structure of Rhombohedral Lead Metaniobate
Journal article, Peer reviewed
Permanent lenke
http://hdl.handle.net/11250/298560Utgivelsesdato
2014Metadata
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- Institutt for materialteknologi [2553]
- Publikasjoner fra CRIStin - NTNU [38525]
Sammendrag
Lead metaniobate (PbNb2O6) can exist both as a stable rhombohedral and a metastable
orthorhombic tungsten-bronze-type polymorph. While the orthorhombic is a
well-known ferroelectric material, the rhombohedral polymorph has been far less studied.
The crystal structure and energetic stability of the stable rhombohedral polymorph
of lead metaniobate is re-examined by powder X-ray diffraction and powder neutron
diffraction in combination with ab-initio calculations. We show that this structure is
described by the polar space group R3, in contradiction to the previously reported
space group R3m. The crystal structure is unusual, consisting of edge-sharing dimers
of NbO6/2 octahedra forming layers with six- and threefold rings of octahedra, and
lead ions in channels formed by these rings. The layers are connected by corner-sharing
between octahedra. Finally, the crystal structure is discussed in relation to other AB2O6
compounds with B = Nb, Ta.