HfTe5andZrTe5: Possible polaronic conductors

The interpretation of the published electrical transport data of the group IVB transition-metal pentatellurides, ${\mathrm{ZrTe}}_5$ and ${\mathrm{HfTe}}_5,$ have been reconsidered. These materials evince a strong resistivity peak at a temperature where the Hall effect and the thermopower manifest a change in sign. Inspired by recent investigations of the “metal-insulator transition” in rare-earth manganates, the anomalous behavior of the pentatellurides have been tentatively interpreted as consequences of polaronic transport.