Physical properties of the misfit-layered (Bi,Pb)-Sr-Co-O system: Effect of hole doping into a triangular lattice formed by low-spin Co ions

Abstract

Pb-doping effect on physical properties of misfit-layered ͑Bi,Pb͒-Sr-Co-O system, in which Co ions form a two-dimensional triangular lattice, was investigated in detail by electronic transport, magnetization and, specific-heat measurements. Pb doping enhances the metallic behavior, suggesting that carriers are doped. Pb doping also enhances the magnetic correlation in this system and increases the magnetic transition temperature. We found the existence of the short-range magnetic correlation far above the transition temperature, which seems to induce the spin-glass state coexisting with the ferromagnetic long-range order at low temperatures. Specific-heat measurement suggests that the effective mass of the carrier in ͑Bi,Pb͒-Sr-Co-O is not enhanced so much as reported in NaCo 2 O 4 . Based on these experimental results, we propose a two-band model that consists of narrow a 1g and rather broad e g Ј bands. The observed magnetic property and magnetotransport phenomena are explained well by this model. FIG. 1. ͑a͒ A schematic picture of the crystal structure of Bi-Sr-Co-O. ͑b͒ A projected view of hexagonal CoO 2 layer into the a-b plane.

Enhancement of the thermoelectric properties of directionally grown Bi–Ca–Co–O through Pb for Bi substitution

“…This behaviour can be explained by the Pb substitution effect on the TE phase. 19 Fig . 7 shows the variation of the Seebeck coefficient with the temperature, as a function of the Pb content.…”

Transport Properties and Cationic Substitutions in Sr2IrO4

“…Co-based oxides with a low-spin (LS) state, such as Na x CoO 2 21 or misfit layered compounds 22,23 show interesting thermoelectric properties with the best ZT values at high temperature among oxides. In particular, their thermoelectric power is largely enhanced for metallic oxides.…”

Layered Cobaltites and Natural Chalcogenides for Thermoelectrics

“…Dimension less figure of merit ZT = S 2 T/ρκ reflects total thermoelectric performance (see Figure 5c and f). [41], in-plane resistivity ρ ab also shows metallic behavior around room temperature, while it arises minimum near 80 K and diverges with further decreasing the temperature. Resistivity ρ ab value of single crystal for x = 0.0 at room temperature is ∼4 mOhm×cm and is smaller than that of our polycrystalline sample (∼15 mOhm×cm).…”

“…It is noted that variation of R H with Pb doping is also similar to that of ρ ab . Pb doping slightly reduces the magnitude of R H ,b u tt h ei n c r e a s ei nn u m b e ro fc h a r g ec a rriers is much smaller than expected from chemical composition [41,44].…”