SYNTHESIS AND THERMOELECTRIC PROPERTIES OF MATERIALS BASED ON LAYERED BISMUTH AND CALCIUM COBALTITES

DOI: 10.6060/tcct.20165912.5465
Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2016. V. 59. N 12. P. 87-92

The excessive industry and transport heat can be converted into electrical energy by means of thermoelectric generators (TEG). This provides interest for development of alterna-tive energy sources and also reduces environment "heat pollution". For development of TEG the materials with both high values of electrical conductivity and thermo-EMF coefficient and low thermal conductivity are required. Such complex of properties is observed for ceramics based on layered cobaltites of sodium, calcium and bismuthcalcium. Thermoelectric char-acteristics of oxide ceramics can be enhanced by chemical or phase inhomogenity creation. Thus, effective oxide thermoelectric development in present work Ca2.7Bi0.3Co4O9+–Bi2Ca2Co1.7Oy composite materials had been prepared and investigated as possible materials for p-branches of high-temperature TEG of new generation. (1–x)Ca2.7Bi0.3Co4O9+–xBi2Ca2Co1.7Oy ceramic samples (x = 0.0–1.0) were prepared using solid-state reactions method from CaCO3, Bi2O3 and Co3O4 in air in the temperature range of 1073–1133 K. The samples phase composition was characterized by X-ray diffraction (XRD) analysis using Bruker D8 XRD Advance with monochromatic CuK radiation ( = 1.5406 Å). Thermal ex-pansion, electrical conductivity () and thermo-EMF (Seebeck) coefficient (S) of ceramics were studied in air in the temperature range of 300–1100 K. The power factor values of the samples were calculated using equation P = S2. Ca2.7Bi0.3Co4O9+ (x = 0.0) and Bi2Ca2Co1.7Oy (x = 1.0) samples were monophase, whereas (1–x)Ca2.7Bi0.3Co4O9+–xBi2Ca2Co1.7Oy (x = 0.2–0.8) ceramics was heterogeneous and consisted of Ca2.7Bi0.3Co4O9+ solid solution and layered cobaltite of bismuth–calcium Bi2Ca2Co1.7Oy. The values of linear thermal expansion coefficient (LTEC) varied in the range of (9.82–11.4)10–6 K–1 with a min-imum for the composite with x = 0.6 and minimal LTEC values were observed for ceramics with a predominance of layered bismuth–calcium cobaltite. The obtained materials were p-type conductors and their conductivity changed its character from semiconducting (x  0.6) to metallic (x  0.8) and electrical conductivity values decreased but thermo-EMF coefficient increased with x. The values of Seebeck coefficient and power factor of the samples in-creased with temperature and were maximal for Ca2.7Bi0.3Co4O9+, Bi2Ca2Co1.7Oy and 0.6Ca2.7Bi0.3Co4O9+–0.4Bi2Ca2Co1.7Oy samples – 90–100 W/(mK2) near 1100 K. It was shown that large values of thermo-EMF coefficient of monophase and composite ceramics based on the layered calcium and bismuth–calcium cobaltites indicate the possibility of its usage for high-temperature thermoelectroconversion.

Key words: oxide thermoelectrics, electrical conductivity, thermo-EMF coefficient, power factor, thermal expansion

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2016, Т. 59, № 12, Стр. 87-92

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