Preparation and Thermoelectric Properties of Co-Doped ZnO Synthesized by Sol–Gel

Abstract

Zinc oxide (ZnO) has attracted increasing attention as one of the most promising n-type thermo-electric materials, but its practice use was limited by high thermal conductivity and low electrical conductivity. Therefore, we herein prepared Co-doped ZnO nanoparticles by sol-gel method and then compressed nanoparticles into bulk materials through spark plasma sintering. The thermo-electric properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and ZT value, have been investigated. We found that the substitution of Co2+ causes the decrease of bandgap and the increase of carrier concentration, thus the improvement of electrical conductivity. At the same time, the Co-induced lattice distortion and nanoparticles reduce the thermal conductivity by shortening the mean free path (MFP) of the phonons. The resultant ZT is 0.037 for Zn0.9Co0.1O, which is more than 23-fold higher than that of the pure ZnO samples.

Structural, optical, thermoelectrical, and magnetic study of Zn1‐xCoxO (0 ≤ x ≤ 0.10) nanocrystals

“…It can be seen that the power factor PF = dS 2 ( Figure 10A), and finally, the thermoelectric conversion efficiency (ZT) ( Figure 10B), has been improved compared to previous similar work. 17…”

“…Thermoelectric properties can be recovered by reducing thermal conductivity (κ), and increasing electrical conductivity (σ), and Seebeck coefficient ( S ). Experimental and theoretical studies suggest that substitution ZnO with transitional metal elements (M‐ZnO) such as Mn, Ce, Co, Ni, and Al can improve optical, electrical, and thermoelectric properties . Cobalt has received much recognition as a candidate material because the ionic radius of Co 2+ is close to that of Zn 2+ (a Co 2+ = 0.058 nm, a Zn 2+ = 0.06 nm).…”

“…Experimental and theoretical studies suggest that substitution ZnO with transitional metal elements (M-ZnO) such as Mn, Ce, Co, Ni, and Al can improve optical, electrical, and thermoelectric properties. [17][18][19][20][21][22][23][24][25][26][27] Cobalt has received much recognition as a candidate material because the ionic radius of Co 2+ is close to that of Zn 2+ (a Co 2+ = 0.058 nm, a Zn 2+ = 0.06 nm). It can be a substitute in the host lattice without disturbing the crystalline structure.…”

An alternative, faster and simpler method for the formation of hierarchically porous ZnO particles and their thermoelectric performance

“…In addition, the sintered T-NZnOP (especially, T-NZnOP-750C and T-ZnOP-950C) obtained results that exhibited an increase in PF which improved the total ZT values as compared to the previous nanostructured undoped ZnO samples. 6,7,49,50 Henceforth, the dimensionless gure of merit (ZT) is as shown in Fig. 6c.…”

Doping Efficiency in Cobalt-Doped ZnO Nanostructured Materials

“…As doping increases, grain size increases and it reduces the charge carrier scattering at grain boundaries, and hence, there is an increase in mobility as well as conductivity [59]. Wu et al [60] prepared cobalt-doped ZnO (0%-10%) by the sol-gel method and showed that the substitution of Co ++ for Zn ++ could improve the electrical conductivity due to the increase in carrier concentration. In addition, we estimated several activation energies using equation (5), indicative of various conduction mechanisms involved in the doped samples.…”