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

A new member, m = 6, Of the series K-x(PO2)(4)(WO3)(2m) has been isolated a nd studied by single crystal X-ray diffraction and electrical transport mea surements. The structure corresponds to that of the MonoPhosphates Tungsten Bronzes with hexagonal tunnels (MPTBh's). It has been solved and refined t o conventional R = 0.0268 with 2342 independent reflections with I> 3 sigma (I). The unit cell is monoclinic (space group P2(1)/m) with a = 6.6736(2), b=5.3543(3), c=11.9005(5) Angstrom, beta = 92.615(3)degrees. The oxygen sur roundings of K; P and W atoms are described and compared with those of othe r members of the series including Pb-, Na- and K-based analogues. Electrica l properties and correlations with structural data are discussed. Large mag netoresistance effects have been observed at low temperature and assigned t o possible CDW instabilities.