Transport and Magnetic Properties of Magnéli Phase Tungsten Oxide WO2.90 Prepared by Spark Plasma Sintering

Abstract

The transport and magnetic properties of the Magnéli phase tungsten oxide WO_2.90, prepared via spark plasma sintering, were investigated across a broad temperature range of 4–550 K, including the previously unexplored low-temperature region below 300 K. Microstructure analysis shows that obtained pellets are fully dense, enabling reliable measurement of transport properties. Resistivity measurements reveal typical metallic behavior of WO_2.90 at low temperatures. Above room temperature, resistivity tends to saturate by reaching a maximum value near 430 K. The resistivity saturation indicates that Mott-Ioffe-Regel limit is approached, where the charge carrier mean free path becomes comparable to the interatomic spacing. The temperature dependence of the resistivity can be well described by the phenomenological parallel resistor model. Significant positive magnetoresistance was observed at low temperatures, with an unusual linear dependence on the magnetic field. Despite its metallic conductivity, WO_2.90 displays weak diamagnetism, likely due to the substantial core diamagnetism of tungsten and the bipolaronic pairing of charge carriers.