Commensurate-incommensurate transition in the charge-density-wave state ofK0.30MoO3

The ‘‘blue bronze’’ ${\mathrm{K}}_{0.30}$ ${\mathrm{MoO}}_3$ has a charge-density wave (CDW) which forms at T=181 K. At temperatures below 181 K, nonlinear conductivity due to charge transport by the CDW has been observed. We have performed x-ray and elastic-neutron-scattering experiments which show that at onset the CDW is incommensurate with a reduced wave vector of q→=(0, 0.263, 0.5). The $b^{\mathrm{*}}$ component of q→ is temperature dependent and the incommensurability δ=q-$b^{\mathrm{*}}$/4 decreases to zero near T=100 K. Measurements of the threshold electric field for nonlinear charge transport show a broad decrease as the temperature is lowered beginning near 100 K. No increase of the threshold field in the commensurate CDW phase is inconsistent with the depinning of a rigid CDW, but may be explained by the transport of CDW phase solitons or dislocations.