Synergistic effects of zirconium- and aluminum co-doping on the thermoelectric performance of zinc oxide

Abstract

This work aims to explore zirconium as a possible dopant to promote thermoelectric performance in bulk ZnO-based materials, both within the single-doping concept and on simultaneous codoping with aluminum. At 1100-1223 K mixed-doped samples demonstrated around ~2.3 times increase in ZT as compared to single-doped materials, reaching ~0.12. The simultaneous presence of aluminum and zirconium imposes a synergistic effect on electrical properties provided by their mutual effects on the solubility in ZnO crystal lattice, while also allowing a moderate decrease of the thermal conductivity due to phonon scattering effects. At 1173 K the power factor of mixeddoped Zn0.994Al0.003Zr0.003O was 2.2-2.5 times higher than for single-doped materials. Stability tests of the prepared materials under prospective operation conditions indicated that the gradual increase in both resistivity and Seebeck coefficient in mixed-doped compositions with time may partially compensate each other to maintain a relatively high power factor.

Exploring Tantalum as a Potential Dopant to Promote the Thermoelectric Performance of Zinc Oxide

“…All the observed reflections can be indexed in a hexagonal wurtzite structure, space group (SG) P6 3 mc (Figure 1C), typical for ZnO-based ceramics processed under the described conditions. The samples x = 0.006 and 0.008 showed the presence of weak reflections marked by arrows in the inset in Figure 1B, which are likely to correspond to ZnTa 2 O 6 phase, in agreement with the literature data [16,17,18]. The observed changes in the lattice parameters (Figure 1C), however, suggest that the tantalum addition also significantly affects the wurtzite unit cell size.…”

“…The spectra were acquired in the UV–Vis range (250–825 nm) with a step of 0.2 nm. Measurements techniques for the total electrical conductivity ( σ ) and Seebeck coefficient ( α ), and corresponding procedures for ZnO-based samples are described elsewhere [17,18,26]. Similar thermal equilibration profiles were used for the thermal diffusivity ( D ) and specific heat capacity ( C p ) studies (Netzsch LFA 457 Microflash and a Netzsch DSC 404F1 equipment, correspondingly).…”

“…The most typical and commonly used dopant to explore various material design concepts is aluminium [7,8,9]; other representative examples include indium, iron, bismuth, nickel [10,11,12,13], etc. A promising strategy includes co-doping with various cations, in some cases leading to synergistically enhanced performance due to combined effects on the solubility in wurtzite lattice and microstructural evolution [14,15,16,17,18]. Doping with higher valence cations was also attempted, relying on more efficient electron doping effects due to the charge difference with Zn 2+ cation [16,17,19].…”

“…A promising strategy includes co-doping with various cations, in some cases leading to synergistically enhanced performance due to combined effects on the solubility in wurtzite lattice and microstructural evolution [14,15,16,17,18]. Doping with higher valence cations was also attempted, relying on more efficient electron doping effects due to the charge difference with Zn 2+ cation [16,17,19].…”

Review on texturization effects in thermoelectric oxides

“…Lately, Al and Zr codoping have been found to be a promising combination in the ZnO matrix which would suppress the thermal conductivity and boost electrical conductivity. Zn 0.997 Al 0.002 Zr 0.005 O showed a ZT of 0.12 at 1173 K. This mixed combination was seen to exhibit the lowest thermal conductivity and better ZT than the individual-doping compositions [94]. Dy doping has been tried in the ZnO matrix by Anju et al Since Dy possess higher ionic radii and since they produce localised magnetic moment due to unpaired electron, it can effectively act as the phonon scatterer and lead to reduction in thermal conductivity.…”