Commensurate-incommensurate transition in the charge-density-wave state of K0.30MoO3

The blue bronze K0.30MoO3 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* component of q is temperature dependent and the incommensurability =q-b*/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.