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

Role of Ag in textured-annealed Bi2Ca2Co1.7Ox thermoelectric ceramic

“…On the other hand, when observing the figure it is clear that, at least, some part of Ag is kept as metallic one, in agreement with previously reported data in similar systems [34,35]. On the other hand, it could be considered that some part of Ag might be inserted in the crystal structure [25,36] due to the similar ionic radii of Ag + , Bi 3+ , and Ca 2+ . In order to check if some Ag is substituting these cations in the RS layer, cell parameters have also been determined from the Rietveld refinement and the results are displayed in Table II.…”

High temperature thermoelectric properties of co-doped Ca3−xAgxCo3.95Fe0.05O9+δ (0≤x≤0.3)

“…On the basis of charge neutrality, the substitution of Ag þ for Ca 2 þ introduces hole charge carriers into the system. Similar results were found for the Ca 3À x Ag x Co 4 O 9 þ δ system [14][15][16]. Wang et al [15] studied the transport properties of Ca 3À x Ag x Co 4 O 9À δ (x¼ 00.0-0.3), where they found that the hole carrier concentration increased with increasing Ag content.…”

“…It has been reported that partial substitution for Ca by heavier ions with trivalence such as Eu 3 þ [7], Nd 3 þ [11], Bi 3 þ [5], Gd 3 þ [12] and Yb 3 þ [13], is effective in improving thermoelectric properties. Besides, the monovalent silver ion substitution on the Ca site has been found to reduce electrical resistivity and increase thermopower simultaneously, which in turn results in power factor enhancement [14][15]. We have recently reported the effect of Ag on the low-temperature thermoelectric properties of Ca 3À x Ag x Co 3.95 Fe 0.05 O 9 þ δ (0rxr0.3) [16].…”

Thermoelectric properties of transition metals-doped Ca3Co3.8M0.2O9+δ (M = Co, Cr, Fe, Ni, Cu and Zn)

“…However, the previous studies did not show any consistency of the S dependence and different methods were used to interpret different results. The first way is to use the model based on the modified Heikes formula [17,18,20,22,26,41] S ¼ À j B e ln g 3 g 4 …”

“…The substitution can take place either at the Ca-site or at the Co-site. There have been a number of reports on partially substituted elements at Ca-site, for instance, Na [11][12][13][14], Y [8], Ag [15][16][17][18], Bi [12,19], Ba [18], Nd [14], Gd [20], Yb [21], and other rare earth elements [22][23][24]. The effect of partial substitution at the Ca-site is mainly to change the charge carrier concentration which results in a change in resistivity.…”