Crystal structure and electrical properties of K2P4W12O44, the m=6 member of the series of low-dimensional conductors Kx(PO2)4(WO3)2m

Abstract

A new member, m=6, of the series K _x (PO ₂ ) ₄ (WO ₃ ) _2m has been isolated and studied by single crystal X-ray diffraction and electrical transport measurements. The structure corresponds to that of the MonoPhosphates Tungsten Bronzes with hexagonal tunnels (MPTBh's). It has been solved and refined to conventional R=0.0268 with 2342 independent reflections with I>3σ(I). The unit cell is monoclinic (space group P2 ₁ /m) with a=6.6736(2), b=5.3543(3), c=11.9005(5) Å, β=92.615(3)°. The oxygen surroundings of K, P and W atoms are described and compared with those of other members of the series including Pb-, Na- and K-based analogues. Electrical properties and correlations with structural data are discussed. Large magnetoresistance effects have been observed at low temperature and assigned to possible CDW instabilities.