Phase formation and magnetotransport of alkali metal doped Na_(0.75)CoO_2 thermoelectric oxide

摘要

Synthesis and characterization of bulk Na_xCoO_2 samples substituted by K and Rb is reported. Phase formation studies revealed a narrow stable region for Na-alkali metal-Co system. Whisker and platelike single crystalline structures have been found to form on the surface of the pellets in case of K doping. All samples were metallic and no characteristic anomaly in R-T curves was observed for Rb doped sample. Magnetoresistance measured has a pronounced positive response only for K-doped and pure Na_xCoO_2 phases, reaching 11% and 7% at 5 K temperature, respectively.