An enhancement ZT and spin state transition of Ca3Co4O9 with Pb doping

Tuning of conductive type and magnetic properties of Ca3Co2O6 ceramics through Pb‐doping

“…In order to further understand the intrinsic physical properties along with the element‐doping effect of this spin‐chain compound, we performed a systematic study on the Pb‐doping effect of Ca 3− x Pb x Co 2 O 6 ( x =0‐0.3) ceramics. The purpose of choosing Pb as the dopant is that Pb‐doping can optimize the morphology, carrier concentration, phonon frequency effectively in the layered cobaltite materials, leading to a considerable improvement of its TE performance. Moreover, the possible mixed valence states of the doped Pb ions may also have an influence on the valence or spin state of Co ions in this cobalt‐based compound and then its macroscopic properties.…”

“…The unit cell volume V has a similar change trend with that of lattice parameter c . This phenomenon is similar to that of the Pb‐doped Ca 3 Co 4 O 9 compound reported by Demirel et al . The structural parameter variation may be related to the ionic radius difference between Ca 2+ and the doped Pb 2+ or Pb 4+ ions.…”

“…The value of ZT 300 K for Pb‐doped sample with x =0.2 is about four times larger than the un‐doped sample. Although the room‐temperature ZT value for the Pb‐doped Ca 3 Co 2 O 6 is still smaller than the layered cobalt oxide thermoelectric material Ca 3 Co 4 O 9 due to the relative larger resistivity at room‐temperature, the good thermal stability of Ca 3 Co 2 O 6 may give a promising result at high temperatures.…”

High-temperature thermoelectric properties of Na- and W-Doped Ca3Co4O9 system

“…Chemical substitution of alternate metal cations at both Ca-and Co-sites of Ca 3 Co 4 O 9 is another approach that has been used to ne tune the electrical and thermal transport properties of TE oxides. These studies include partial substitution of Na, Bi, Y, Ag, Nd, Sr and Pb ions [25][26][27][28][29][30][31][32] at Ca-sites, which adjusts the carrier concentration without changing much the band structure of materials, and substitution of Fe, Mn, Cu, Ti, Ga, Mo, W and In ions [33][34][35][36][37][38] at Cosites with signicant changes in the band structure and transport mechanism. In another research work, it was reported that doping of Na ions at Ca-sites resulted in decrease of electrical resistivity and as a consequence increase of thermoelectric power factor to $5.5 Â 10 À4 W m À1 K À2 at 1000 K, though thermal conductivity (k) of these samples was still too high (4.0 W m À1 K À1 ), impeded the further improvement of zT values.…”

Synthesis and structural properties of thermoelectric Ca3−xAgxCo4O9+δ powders

“…It has been reported that the thermoelectric properties of Ca 3 Co 4 O 9 are improved by substituting Ti 4+ , Ag + , Ba 2+ , Pb 2+ , and Pr 3+ for Co 3+ and by substituting Bi 3+ , Na + , transition metals, and rare earth elements for Ca. 4,6,[9][10][11][12][13][14][15][16][17][18][19] For example, Xu et al 6 reported that when the Ti 4+ content in Ca 3−x Ti x Co 4 O 9 reached 0.3, the Ti 4+ ions existed in both the CoO 2 and Ca 2 CoO 3 layers. The thermal conductivity decreased with Ti 4+ doping.…”