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.