Thermoelectric properties of 0.7 Ca3Co4−xCuxO9/0.3 Bi2Ca2Co2−zCuzOy (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 US 01.09.2017
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Materials Science; Optical and Electronic Materials
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-017-7179-9

0.7 Ca 3 Co 4 O 9 /0.3 Bi 2 Ca 2 Co 2 O y thermoelectric composites were prepared by solid state reaction, and Cu doping in Ca 3 Co 4 O 9 and Bi 2 Ca 2 Co 2 O y was carried out respectively to modify the thermoelectric properties. The crystal structure and micro structure of the 0.7 Ca 3 Co 4− x Cu x O 9 /0.3 Bi 2 Ca 2 Co 2− z Cu z O y 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 Bi 2 Ca 2 Co 2 O y phase distributed randomly in the host phase. The ρ of 0.7 Ca 3 Co 4 O 9 /0.3 Bi 2 Ca 2 Co 2 O y is even lower than that of both constituents. Similar to the ρ -T behavor of Ca 3 Co 4 O 9 , the metal–semiconductor transition around 773 K in the composites 0.7 Ca 3 Co 4−x Cu x O 9 /0.3 Bi 2 Ca 2 Co 2 O y is observed, indicating carrier in Ca 3 Co 4 O 9 contributing a lot to the electrical conductivity. However, as Cu doping in Bi 2 Ca 2 Co 2 O y 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 (Ca 3 Co 4 O 9 ) + 0.3  S (Bi 2 Ca 2 Co 2 O y ). The S of the composites is enhanced by doping Cu in Bi 2 Ca 2 Co 2 O y , but it is depressed as Cu doping carried out in Ca 3 Co 4 O 9 . The power factor of 0.7 Ca 3 Co 3.9 Cu 0.1 O 9 /0.3 Bi 2 Ca 2 Co 1.9 Cu 0.1 O y gets to the maximum 3.8 × 10 −4  W m −1  K −2 at 973 K.