Detailed investigation of the phase transition in   K$_{x}$P$_4$W$_{8}$O$_{32}$ and experimental arguments for a charge density   wave due to hidden nesting
  Detailed structural and magnetotransport properties of the monophosphate tungsten bronze K$_{x}$P$_4$W$_{8}$O$_{32}$ single crystals are reported. Both galvanomagnetic and thermal properties are shown to be consistent with a charge density wave electronic transition due to hidden nesting of quasi - 1D portion of the Fermi surface. We also observe the enhancement of electronic anisotropy due to reconstruction of the Fermi surface at the Peierls transition. The resistivity presents a thermal hysteresis suggesting a first order nature characteristics of a strong coupling scenario. However, other measurements such as the change of carriers density demonstrate a second order Peierls scenario with weak coupling features. We suggest that the structural transition driven by the residual strain in the K - P - O environment is responsible for the resistivity hysteresis and modifes the Fermi surface which then helps the rise to the second order Peierls instability. 
Kamil K. Kolincio, Olivier P\'erez, Sylvie H\'ebert, Pierre Fertey,   and Alain Pautrat
cond-mat.str-el