High-temperature thermoelectric properties of polycrystalline CaMn1-xNbxO3-δ. Issue 8 (1st June 2018)

• Record Type: Journal Article
• Authors: Seo, J.W.; Kim, G.H.; Choi, S.-M.; Park, K.
• Is Part Of: Ceramics international. Volume 44:Issue 8(2018)
• Page Start: 9204
• Page End: 9214
• Publication Date: 2018-06-01
• Subjects: Sintering -- Electron microscopy -- Electrical conductivity -- Electrical properties -- Microstructure-final; Ceramics -- Periodicals; Céramique industrielle -- Périodiques; Ceramics; Periodicals; Electronic journals; 666
• DOI: 10.1016/j.ceramint.2018.02.130
• Languages: English
• ISSNs: 0272-8842

Abstract

Abstract: The structural and thermoelectric (TE) properties of polycrystalline CaMn1- x Nb x O3-δ (0.025 ≤ x ≤ 0.25) were studied with X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and electrical transport measurements, with an emphasis placed on the Nb 5+ content. The CaMn1- x Nb x O3-δ crystallized in an orthorhombic perovskite structure of the Pnma space group. The density and grain size of the CaMn1- x Nb x O3-δ samples gradually decreased when Nb 5+ ions substituted Mn 4+ ions. The CaMn0.95 Nb0.05 O3-δ sample contained charge-ordered domains, stacking faults, and micro-twins. The substitution of Nb 5+ for Mn 4+ up to x = 0.15 led to an increase in electrical conductivity, mainly due to an increased electron concentration. The CaMn1- x Nb x O3-δ samples with low Nb 5+ contents (0.025 ≤ x ≤ 0.15) showed metallic behavior, whereas those with high Nb 5+ contents (0.2 ≤ x ≤ 0.25) showed semiconducting behavior. The Nb 5+ substitution lowered the absolute value of the Seebeck coefficient for the CaMn1- x Nb x O3-δ samples due to an increased electron concentration. The largest power factor (1.19 × 10 −4 W m −1 K −2 ) was obtained for CaMn0.95 Nb0.05 O3-δ at 800 °C. The partial substitution of Nb 5+ for Mn 4+ in CaMnO3-δ proved to be highly effective for improving high-temperature TE properties.