Thermoelectric Properties of Sintered and Textured Nd-Substituted Ca₃Co₄O₉ Ceramics

Abstract

Zn-and Ti-doped thermoelectric misfit cobalt oxides Ca 3 Co 4-x-y Zn x Ti y O 9 (x = 0-0.5, y = 0-0.5) were prepared by solid-phase reaction, sequent uniaxial compression molding and sintering at 1173 K for 20 h. Powder X-ray diffraction data suggest that Zn and Ti dopants substitute in the rocksalt layer rather than in the CoO 2 layer for x ≤ 0.1 and y ≤ 0.1, respectively. In Zn and Ti single-doped samples for x ≤ 0.1 and y ≤ 0.1, ZT at room temperature increased with x and y through an increase in the absolute Seebeck coefficients despite the decrease in electrical conductivities. In Zn and Ti double-doped samples, minor phases other than the misfit oxides were observed at approximately x + y ≥ 0.1. At x ≤ 0.1 and y ≤ 0.1 double doping improved the thermoelectric properties. ZT at room temperature reached a maximum value of 0.035 at (x, y) = (0.1, 0.03).

High-temperature thermoelectric properties of late rare earth-doped Ca3Co4O9+δ

“…Many attempts have been made to optimize the thermoelectric performance of Ca 3 Co 4 O 9+ı by either partially substituting cations or using appropriate fabrication methods such as hot-pressing (HP) or spark plasma sintering (SPS) techniques. Partial replacement of cations in Ca 3 Co 4 O 9+ı have been carried out on either the Ca site [10][11][12][13][14][15][16][17][18][19][20][21] or the Co sites. [22][23][24][25] It has been reported that partial substitution for Ca by heavier ions with trivalence such as Eu 3+ [10], Nd 3+ [11], Bi 3+ [12], Y 3+ [14], Yb 3+ [18] Gd 3+ and Y 3+ [19] is effective in improving thermoelectric properties, e.g., ZT ≈ 0.25 for the Bi-doped and ZT ≈ 0.3 for the Eu-doped samples at ca.…”

The effects of dual doping on the thermoelectric properties of Ca3−xMxCo4−yCuyO9 (M=Na, La)

“…The other approach focuses on partial substitution of cations to adjust the carrier concentrations and thus tune the electric and thermal transport characteristics of thermoelectric oxides. These include using Na, [14,15] Bi, [16,17] Ag, [18][19][20] La, [21,22] Nd, [23,24] Y, [25] Sr, [26] Gd [27] and Lu [28,29] for the Ca-site doping, which changes the carrier concentration without influencing the band structure much, and Fe, [30,31] Cu, [30,31] Ga, [32] Zn, [33] Mn, [30,31] Ag, [34] Ti, [35] Ni, [31] for the Co-site doping, which can cause changes in both band structure and transport mechanism [36][37][38].…”

Texture and high temperature transport properties of AgxCa3−xCo4O9 (0≤x≤0.6) compounds

“…Lu). metals is one of them [6][7][8]. Some reports revealed that electrical properties of Ca 3 Co 4 O 9 could be enhanced by means of substituting Ag for Ca site or adding Ag 2 O to Ca 3 Co 4 O 9 polycrystalline matrix [9][10][11], but there were no further reports on Ag substitution effects on both texture and transport mechanism of Ag x Ca 3−x Co 4 O 9 to date.…”