Low temperature thermopower and electrical transport in misfit Ca₃Co₄O₉ with elongated c-axis

Abstract

The temperature dependence of the electrical resistivity (ρ) and thermopower (S) of misfit cobaltite Ca₃Co₄O₉ has been studied. The compound is a promising thermoelectric material, exhibiting very low ρ(∼1.3 × 10⁻⁴ Ω cm) and reasonably high S (∼56 μV K⁻¹) at room temperature, which is desirable for thermoelectric applications. At T < 80 K, S exhibits T^3/2 dependence, suggesting that electron–magnon scattering has a pronounced influence on S at low temperatures. Ca₃Co₄O₉ exhibits a temperature independent power factor in the temperature range 300–80 K. A comparison of the temperature dependence of the power factor of Ca₃Co₄O₉ with various materials projected or used as a thermoelectric cooler (e.g. single crystal of short c-axis Ca₃Co₄O₉, polycrystalline La_0.95Sr_0.05CoO₃, Bi_0.85 Sb_0.15, Bi₂Te₃, Bi-SiO₂ composite) indicates that title compound Ca₃Co₄O₉ is a much superior candidate for thermoelectric applications.