TY - JOUR
T1 - Enhancing the Thermoelectric Performance of Calcium Cobaltite Ceramics by Tuning Composition and Processing
AU - Yu, Jincheng
AU - Chen, Kan
AU - Azough, Feridoon
AU - Alvarez-ruiz, Diana T.
AU - Reece, Michael J.
AU - Freer, Robert
N1 - Funding Information:
The authors are grateful to the EPSRC for the provision of funding for this work (EP/H043462, EP/I036230/1, EP/L014068/1, and EP/L017695/1 acknowledged by R.F.). The work was also supported by the Henry Royce Institute for Advanced Materials, funded through EPSRC Grants EP/R00661 X/1, EP/S019367/1, EP/P025021/1, and EP/P025498/1. We gratefully acknowledge the support from X-ray facilities in the Department of Materials in the University of Manchester. J.Y. thanks China Scholarship Council for their financial support during his Ph.D. program. All research data supporting this work are directly available within this publication.
Publisher Copyright:
© 2020 American Chemical Society.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2020/10/21
Y1 - 2020/10/21
N2 - Calcium cobaltite (Ca3Co4O9) is a promising p-type thermoelectric oxide material. Here, we present an approach to optimize the thermoelectric performance of Ca3Co4O9 by controlling the chemical composition and fabrication process. Ca3–xBixCo3.92O9+δ (0.1 ≤ x ≤ 0.3) and Ca2.7Bi0.3CoyO9+δ (3.92 ≤ y ≤ 4.0) ceramics were prepared by Spark Plasma Sintering (SPS). Stoichiometric mixtures of raw materials were combined and calcined at 1203 K for 12 h, followed by SPS at 1023 K for 5 min at 50 MPa. The samples were subsequently annealed at 1023 or 1203 K for 12 h in air. XRD and HRTEM analyses confirmed the formation of the cobaltite misfit phase with minor amounts of secondary phases; SEM-EDS showed the presence of Bi-rich and Co-rich secondary phases. After annealing at 1203 K, the secondary phases were significantly reduced. By controlling the cobalt deficiency and level of bismuth substitution, the electrical conductivity was enhanced without degrading Seebeck coefficients, promoting a high power factor of 0.34 mW m–1 K–2 at 823 K (parallel to the ab planes, //ab). Due to enhanced phonon scattering, the thermal conductivity was reduced by 20%. As a result, a highly competitive ZT(//ab) of 0.16 was achieved for Ca2.7Bi0.3Co3.92O9+δ ceramics at 823 K.
AB - Calcium cobaltite (Ca3Co4O9) is a promising p-type thermoelectric oxide material. Here, we present an approach to optimize the thermoelectric performance of Ca3Co4O9 by controlling the chemical composition and fabrication process. Ca3–xBixCo3.92O9+δ (0.1 ≤ x ≤ 0.3) and Ca2.7Bi0.3CoyO9+δ (3.92 ≤ y ≤ 4.0) ceramics were prepared by Spark Plasma Sintering (SPS). Stoichiometric mixtures of raw materials were combined and calcined at 1203 K for 12 h, followed by SPS at 1023 K for 5 min at 50 MPa. The samples were subsequently annealed at 1023 or 1203 K for 12 h in air. XRD and HRTEM analyses confirmed the formation of the cobaltite misfit phase with minor amounts of secondary phases; SEM-EDS showed the presence of Bi-rich and Co-rich secondary phases. After annealing at 1203 K, the secondary phases were significantly reduced. By controlling the cobalt deficiency and level of bismuth substitution, the electrical conductivity was enhanced without degrading Seebeck coefficients, promoting a high power factor of 0.34 mW m–1 K–2 at 823 K (parallel to the ab planes, //ab). Due to enhanced phonon scattering, the thermal conductivity was reduced by 20%. As a result, a highly competitive ZT(//ab) of 0.16 was achieved for Ca2.7Bi0.3Co3.92O9+δ ceramics at 823 K.
KW - Annealing temperature
KW - Bismuth substitution
KW - Cobalt deficiency
KW - Cobaltite
KW - Oxide thermoelectric
U2 - 10.1021/acsami.0c14916
DO - 10.1021/acsami.0c14916
M3 - Article
SN - 1944-8244
VL - 12
SP - 47634
EP - 47646
JO - ACS applied materials & interfaces
JF - ACS applied materials & interfaces
IS - 42
ER -