TY - JOUR

T1 - Improved thermoelectric properties in ceramic composites based on Ca3Co4O9 and Na2Ca2Nb4O13

AU - Hinterding, Richard

AU - Wolf, Mario

AU - Jakob, Matthias

AU - Oeckler, O.

AU - Feldhoff, Armin

N1 - Funding Information: Further analysis regarding the newly formed CNO was performed by TEM measurements in Fig. 5. The cross-section of a former NCNO plate and the respective EDXS mapping are given in Fig. 5a,d. The irregular shape at the surface and the introduction of Co into the CNO as found in the SEM results can be recognized. The elemental distribution of Ca, Co and Nb is also rather homogeneous within the CNO particle. The CCO plate crossing the CNO particle also shows a loss of Co and a gain of Nb, resulting in a Ca:Co ratio of 1.08 and a Ca:Nb ratio of 1:0.17. This supports the assumption of a cation exchange between the CCO and the NCNO as the Ca:(Co,Nb) ratio is at 1:1.25 and therefore close to the original Ca:Co ratio of 1:1.33. Again, no new phase with Na as a major element was found in the close vicinity of the CNO particle. EDXS showed only trace amounts of Na within the CNO and no Na within the CCO particle. Therefore, the Na is most likely located within some CoO in the CCO matrix as suggested by Fig. S1 or evaporated to some extent during sintering. The CNO phase was also investigated by SAED and HRTEM for the zone axes [112] in Fig. 5b and c and for [001] in Fig. 5e and f. Both zone axes gave a clear diffraction pattern at the marked location of Fig. 5a, which allowed the distinct indexing of them. As not the whole particle was oriented simultaneously, polycrystallinity seems reasonable. Furthermore, the [001] orientation in Fig. 5f allowed the determination of the a- and b-axis lattice parameters (5.57 ? and 5.66 ? respectively), which are only slightly larger than the literature data for pure CaNbO3 (5.45 ? and 5.53 ? respectively for ICSD 01-089-0718).This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - project number 325156807. Authors gratefully appreciate technical assistance by F. Steinbach.

PY - 2021/12

Y1 - 2021/12

N2 - The oxide materials Ca3Co4O9 and Na2Ca2Nb4O13 were combined in a new ceramic composite with promising synergistic thermoelectric properties. Both compounds show a plate-like crystal shape and similar aspect ratios but the matrix material Ca3Co4O9 with lateral sizes of less than 500 nm is about two orders of magnitude smaller. Uniaxial pressing of the mixed compound powders was used to produce porous ceramics after conventional sintering. Reactions between both compounds and their compositions were thoroughly investigated. In comparison to pure Ca3Co4O9, mixing with low amounts of Na2Ca2Nb4O13 proved to be beneficial for the overall thermoelectric properties. A maximum figure-of-merit of zT = 0.32 at 1073 K and therefore an improvement of about 19% was achieved by the ceramic composites.

AB - The oxide materials Ca3Co4O9 and Na2Ca2Nb4O13 were combined in a new ceramic composite with promising synergistic thermoelectric properties. Both compounds show a plate-like crystal shape and similar aspect ratios but the matrix material Ca3Co4O9 with lateral sizes of less than 500 nm is about two orders of magnitude smaller. Uniaxial pressing of the mixed compound powders was used to produce porous ceramics after conventional sintering. Reactions between both compounds and their compositions were thoroughly investigated. In comparison to pure Ca3Co4O9, mixing with low amounts of Na2Ca2Nb4O13 proved to be beneficial for the overall thermoelectric properties. A maximum figure-of-merit of zT = 0.32 at 1073 K and therefore an improvement of about 19% was achieved by the ceramic composites.

KW - Calcium cobalt oxide

KW - Ceramic

KW - Composite

KW - Figure-of-merit

KW - Power factor

KW - Reaction sintering

KW - Sodium calcium niobate

KW - Thermoelectrics

UR - http://www.scopus.com/inward/record.url?scp=85119998433&partnerID=8YFLogxK

U2 - 10.1016/j.oceram.2021.100198

DO - 10.1016/j.oceram.2021.100198

M3 - Article

AN - SCOPUS:85119998433

VL - 8

JO - Open Ceramics

JF - Open Ceramics

M1 - 100198

ER -