Structure Sensitive Electronic Properties of Quasi‐Two‐Dimensional η‐Mo4O11 Crystals

The electrical resistivity, Hall effect, and magnetoresistance are measured over the temperature range from 1.5 to 300 K for a number of η-Mo4O11 crystals, that undergo two charge density wave transitions at Tc1 = 105 K and Tc2 = 35 K, prepared by a chemical vapor transport method using TeCl4 (10 and 2 mg/cm3) as a carrier gas. Good samples grown with 10 mg/cm3 TeCl4 have high carrier mobilities, showing quantum oscillations in the magnetoresistance and Hall coefficient at low temperatures. Poor samples grown with 2 mg/cm3 TeCl4 have rather low mobilities and anomalous temperature dependence of resistivity with a negative coefficient, together with a log T-dependence. These behaviors may be due to microscopic structural imperfections, such as excess oxygen or vacancies. Based on these experimental results, a tentative band model for conduction electrons and holes, as well as some localized states lying near the Fermi energy, is proposed.