Two-dimensional electrical resistivity in metal doped molybdenum oxides*

Single crystals of Te₄Mo₂₀O₆₂ and Bi₄Mo₂₀O₆₂ were grown by chemical vapor transport method. These crystals have the intergrowth tungsten bronze structure. Their electrical conductivity shows an anisotropy by factors 20 ~50 reflecting the two-dimensional crystal structure. The in-plane resistivities are less than 100 mΩ·cm. It shows a nonlinear current-voltage characteristic. There also a broad maximum appears below 200 K in the voltage drop at around 30 A/cm². From the measurement of Hall effect it was observed that the carrier is a hole. The mobility of holes increases with increasing current density. The anomaly around 200 K was also observed in the powder X-ray diffraction spectra and in the specific heat. In the X-ray spectra the intensity of peaks with indices (2n 2n n) sharply increased around 200 K. It was concluded that the above behaviors come from the formation of CDW accompanied by a crystal instability.