Synthesis and physical properties of layered BaxCoO2

Abstract

A layered cobaltite Ba_xCoO₂ (x = 0.19, 0.28, 0.30, 0.33) was synthesized by an ion exchange technique from the layered Na_xCoO₂ precursors. The phase composition and physical properties were investigated. Ba_xCoO₂ is isomorphic to the precursor Na_xCoO₂. The magnetic susceptibility of Ba_xCoO₂ decreases with increasing barium content and shows a Curie–Weiss-like behavior at temperatures above 50 K. The resistivity is sensitive to the barium content. As the barium content increases from 0.19 to 0.33, a crossover from a semiconducting behavior to a metallic behavior was observed. The Seebeck coefficient of Ba_xCoO₂ is insensitive to the barium content due to the tradeoff effect between the carrier concentration and the Co⁴⁺ content, while the thermal conductivity increases with the increasing barium content from 0.19 to 0.33 owing to the ordered state of Ba ions between the CoO₂ layers.