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, K_0.30-xRbₓMoO₃, disorder is introduced on the alkali sublattice while in the alloy system, K0.30Mo_1-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 K0.30Mo_1-xWₓO₃ system suggest that the low-temperature CDW coherence length becomes very short at low tungsten concentrations.