Dramatic impurity effects on the charge-density wave in potassium molybdenum bronze

Potassium molybdenum bronze, K0.30MoO3, undergoes a charge-density-wave (CDW-) driven phase transition at 180 K, below which nonlinear current-voltage characteristics are observed. Behavior is similar to that observed in NbSe3 and is currently understood based on models which involve charge transport by the CDW. The effects of impurities on CDW phenomena has been a subject of considerable interest. Two types of substitutional doping are possible in the K0.30MoO3 structure. In the alloy system, K0.30-xRbxMoO3, disorder is introduced on the alkali sublattice while in the alloy system, K0.30Mo1-xWxO3, the isoelectronic element tungsten is substituted for molybdenum. We show that the effects of tungsten substitution are very large, larger than such doping effects in other CDW systems, whereas alkali substitution produces only small effects. The data obtained on the K0.30Mo1-xWxO3 system suggest that the low-temperature CDW coherence length becomes very short at low tungsten concentrations.