Thermoelectric properties of 0.7 Ca3Co4−x Cu x O9/0.3 Bi2Ca2Co2−z Cu z O y (x = 0, 0.05, 0.1; z = 0, 0.05, 0.1) composites

• Published in: Journal of materials science. Materials in electronics Vol. 28; no. 18; pp. 13414 - 13419
• Main Authors: Liu, X. R., Li, S. Y., He, Y., Lu, Y., Jin, Y. R., Feng, N. B.
• Format: Journal Article
• Language: English
• Published: New York Springer Nature B.V 01.09.2017
• Subjects: Composite materials; Constituents; Crystal structure; Doping; Electrical resistivity; Electron microscopes; Power factor; Scanning electron microscopy; Seebeck effect; Temperature dependence; Thermoelectricity; X-ray diffraction; X-rays
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-017-7179-9

0.7 Ca3Co4O9/0.3 Bi2Ca2Co2Oy thermoelectric composites were prepared by solid state reaction, and Cu doping in Ca3Co4O9 and Bi2Ca2Co2Oy was carried out respectively to modify the thermoelectric properties. The crystal structure and micro structure of the 0.7 Ca3Co4−xCuxO9/0.3 Bi2Ca2Co2−zCuzOy with x = 0, 0.05, 0.1, and z = 0, 0.05, 0.1 was analyzed using X-ray diffraction and scanning electron microscopy. Temperature dependence of electrical resistivity (ρ) and Seebeck coefficient (S) of the composites was studied from 373 to 973 K. No impurity is detected in the composites from the XRD patterns. Stripes of Bi2Ca2Co2Oy phase distributed randomly in the host phase. The ρ of 0.7 Ca3Co4O9/0.3 Bi2Ca2Co2Oy is even lower than that of both constituents. Similar to the ρ-T behavor of Ca3Co4O9, the metal–semiconductor transition around 773 K in the composites 0.7 Ca3Co4−xCuxO9/0.3 Bi2Ca2Co2Oy is observed, indicating carrier in Ca3Co4O9 contributing a lot to the electrical conductivity. However, as Cu doping in Bi2Ca2Co2Oy is carried out, the metal–semiconductor transition disappeared. The relationship between S of the composites and that of the constituents satisfies the simplest mixing laws: S = 0.7 S (Ca3Co4O9) + 0.3 S (Bi2Ca2Co2Oy). The S of the composites is enhanced by doping Cu in Bi2Ca2Co2Oy, but it is depressed as Cu doping carried out in Ca3Co4O9. The power factor of 0.7 Ca3Co3.9Cu0.1O9/0.3 Bi2Ca2Co1.9Cu0.1Oy gets to the maximum 3.8 × 10−4 W m−1 K−2 at 973 K.