Fabrication and thermoelectric properties of highly textured Ca9Co12O28 ceramic

Tailoring Ca3Co4O9 microstructure and performances using a transient liquid phase sintering additive

“…However, it should be noticed that the correlation between sample porosity and the grains connectivity may be quite complex, especially if considering specific bonding, promoted by liquid phase sintering. The minimum values measured at room temperature and 800 ºC for the 5 wt.% K 2 CO 3 samples (around 11 and 12 m cm, respectively) are much lower than those obtained in classically sintered materials ( 33 and 40 m cm, respectively) [7]. Furthermore, they are relatively close to the values measured in high-density textured materials, produced by the hot-pressing technique, determined in the ab direction (8, and 6 m cm at RT and 600 ºC, respectively) [20], or SPS and measured in the same direction (about 5, and 6 m cm at RT and 800 ºC, respectively) [28].…”

“…As bulk materials, these oxides usually demonstrate quite low thermoelectric performance, which make them no feasible for any practical applications. Envisaging the increment of ZT, many processing and structural engineering routes were attempted, including cationic substitution in solid state sintered materials [4,5], or taking advantage of their crystallographic nature to align the grains into a preferential direction using well-known techniques such as templated grain growth (TGG) [6], hot-pressing [7], spark plasma sintering (SPS) [8], laser floating zone (LFZ) [9], or the recently developed electrically assisted laser floating zone (EALFZ) [10]. These texturing techniques have been reported to produce bulk high density materials with well oriented grains, leading to enhanced electrical conductivity.…”

High thermoelectric performance in Bi2-xPbxBa2Co2Oy promoted by directional growth and annealing

“…This process would allow enhancing ZT to values close to the obtained in single crystals. Many techniques have been used to produce such grain alignment, as hot-pressing [15], spark plasma sintering (SPS) [16], laser floating zone (LFZ) [17], or the electrically assisted laser floating zone [18], which have shown their ability to improve TE performance of bulk materials by the alignment of grains. [20].…”

Enhancement of mechanical and thermoelectric properties of Ca3Co4O9 by Ag addition

“…This shape anisotropy opens the route to preferentially align the grains along the conducting planes which could help reaching TE properties comparable to those obtained on single crystals. Numerous methods have been reported to be efficient to produce well aligned grains, in these or in similar anisotropic systems, such as hot uniaxial pressing [20], templated grain growth (TGG) [19], spark plasma sintering [21], laser floating zone melting (LFZ) [22], electrically assisted laser floating zone [23], etc. On the other hand, these methods possess some drawbacks due to different factors, as the relatively long treatments required for the first two ones, or the high costs associated with the equipment and the strong dependence of thermoelectric properties on the growth or the texturing speeds for the other ones [19,21,24,25].…”